Nosocomiat Bloodstream Infections Caused by Gentamicin-Resistant Gram-Negative Bacilli
R. L. GUERRANT, M.D. L. J. STRAUSBAUGH,
M.D.
R. P. WENZEL, M.D. B. H. HAMORY, M. A. SANDE,
M.D. M.D.
Charlottesville, Virginia
From the Department of Internal Medicine, University of Virginia School bf Medicine, Charlottesville, Virginia 2290 1. This studywas presented at the U.S. Amikacin Symposium, Unlversity of California Medical School, Los Angeles, California, November 9-10. 1976. Requests for reprints should be addressd to Dr. R. L. Guerrant, University of Virginia School of Medicine, Box 305, Charlottesville, Virginia 22901.
094
June 1977
Gentamicin resistance has emerged since 1971 among gram-negatlve bacilli isolated at the University of Virglnla Hospital. 019,169 gram-negative bacilli isolated in 1971,0.6 per cent were resistant to gentamicin by disc sensitivity testing. of 7,617 isolates in 1975, 7.7 per cent were resistant. Approximately 20 per cent of the Klebsiellae had a minimum inhibitory concentration (MC) 116 pg/ml of gentamicin. Since 1974, gentamicin-resistant gram-negative bacilli have accounted for 20 per cent of nosocomial bacteremias. In 1974-1975, 34 episodes of gentamicln-resistant bacteremia occurred. All were in patients with severe underlying diseases who had been hospitalized for longer than four days; 24 (71 per cent) occurred in patients in intensive care units. The organisms isolated were Klebsiella pneumoniae (12 cases), Klebsietla sp. (five cases), Pseudomonas aeruginosa (five cases), Enterobacter aerogenes (three cases), Serratia marcescens (three cases) and others (seven cases). Ail but one of the bacteremic patients had received prior antibiotics, and 19 of 34 episodes were preceded by gentamicin therapy. Nine patients with bacteremia caused by the gentamicin-resistant strains received one to three weeks of amikacin therapy. All showed clinical improvement and the organism cleared from their bloodstreams; in one patient clinical deafness developed; in two patients bacterial suprainfections developed, and five patients subsequently died of other causes during their hospitalization. The introduction of a new antibiotic into clinical medicine is often followed by the emergence of resistant organisms which eventually limit its usefulness [ 11. Antibiotic resistance has been especially common among people with aerobic gram-negative bacilli, often acquired in hospitals [2-51. Gentamicin sulfate was added to the formulary of the University of Virginia Hospital in 1969, and it rapidly replaced kanamycin as the principal antimicrobial agent for treating patients with life-threatening infections caused by gram-negative enteric bacilli. Bacteremia caused by gentamicin-resistant organisms first appeared in our hospital in March 1974; subsequently, it became a major clinical problem. In this report we describe (1) the emergence
The American Journal of Medlclne
VOlUme 62
NOSOCOMIAL
of gentamicin-resistance
among gram-negative bacilli
isolated
of Virginia
at the University
Hospital
1971 and 1975; (2) the epidemiologic,
TABLE I
between
microbiologic
and clinical characteristics of 34 bacteremic comial infections caused by gentamicin-resistant ganisms in 1974 and 1975; and (3) the therapeutic of amikacin in this setting.
nosoorvalue
MATERIALS AND METHODS In Vitro SusceptibilityStudies. A total of 118 gram-negative bacilli were randomly obtained after speciation from the clinical microbiology laboratory of the University of Virginia Hospital in 1971, and 181 similar isolates were obtained in 1975. Seventeen strains of gentamicin-resistant organisms obtained from blood cultures of patients with bacteremic infections in 1974-1975 were tested against these same aminoglycosides. The minimum inhibitory concentrations (MIC) of gentamicin (Garamycine, Schering Corporation, Kenilworth, N.J.), amikacin (Amikine, Bristol Laboratories, Syracuse, N.Y.), sisomicin (Schering Corporation, Kenilworth, N.J.), tobramycin (Nebcin-R@, Eli Lilly & Co., Indianapolis, Ind.) and netilmicin (Schering Corporation, Kenilworth, N.J.) were determined in beef heart infusion broth (Difco, Detroit, Mich.) using a serial microdilution technic [6]. The MIC was defined as the lowest concentration of drug that inhibited growth following 24 hours of incubation. Strains with an MIC of 8 pg/ml or less were considered to be “sensitive” to the aminoglycoside in question, whereas strains with an MIC greater than 8 pglml were considered to be “resistant.” A further review of all Kirby-Bauer disc sensitivity testing carried out on clinical gram-negative bacillary isolates in the hospital bacteriology laboratory was made for 1971 and 1975.
Appearance of Gentamicin-Resistant Bacteremia in 1974-1975. Patients with bacteremia caused by gentamitin-resistant gram-negative bacilli were identified by (1) the ongoing surveillance system of the hospital epidemiology unit [7] and (2) reviewing the records of all patients with positive blood cultures in the hospital’s microbiology laboratory. These charts were reviewed for the patient’s age, sex, location in the hospital, date of bacteremia, diagnosis, number of days in the hospital prior to the onset of bacteremia, antibiotic therapy given prior to the development of bacteremia, potential sources of bacteremia, operations and procedures, therapy and outcome. All patients had multiple positive blood cultures for gentamicin-resistant gram-negative bacilli, and they were treated for clinically significant infections. In addition, the number and dates of all “nosocomial” bacteremias were determined by an ongoing surveillance system [7]. Nosocomial infections are defined as those for which there is no clinical evidence at the time of hospital admission. Isolates from blood and other sites were identified in the clinical microbiology laboratory using standard methods [8]. Antibiotic susceptibility tests on these isolates were performed with the Kirby-Bauer disc diffusion method using carbenicillin, ampicillin, benzyl penicillin, methicillin, cephalothin, tetracycline, chloramphenicol, streptomycin, vancomycin, kanamycin and gentamicin discs [9]. An organism
BLOODSTREAM
INFECTIONS-GUERRANT
Gentamicin Resistance (MIC 316 pg/ml) Among Clinical Isolates at the University Virginia Hospital in 1971 and 1975 1971
Genus Klebslella Enterobacter Escherichia Proteus Pseudomonas
ET AL.
Strains Tested (no.) 25 18 25 25 25
of
1975”
Resistant (%) 4 0 0 0 0
Strains Tested (no.) 65 22 37 26 31
Resistant (%) 20 14 3 12 16
*Of 7,817 gram-negative bacilli isolated from clinical specimens in 1975, 7.7 per cent were resistant to gentamicin by disc.
was considered to be resistant to gentamicin if the zone of inhibition was less than 12 mm. Eleven of the 12 strains of Klebsiella pneumoniae were tested against types 1, 2,3.4, 5, 6 and 21 antiserums for the quellung reaction. Therapywith Amikacin. Ten of the patientswith nosocomial gram-negative bacillary septicemia received amikacin following isolation of the organism and proof of gentamicinresistance. The drug was administered at a dose of 7.5 mg/kg twice a day intramuscularly or intravenously. Patients were monitored to determine the effectiveness of therapy (blood cultures, temperature and survival) and toxicity (renal, liver and neurologic function), if any.
RESULTS Emergence of Gentamicin-Resistant Organisms 1971-1975. When compared with clinical isolates from 1971, isolates of gram-negative bacilli from 1975 demonstrated a strikingly increased resistance to gentamicin (Table I). A review of disc sensitivity studies on all aerobic gram-negative bacilli isolated from cfinical specimens in 1971 revealed that less than 1 per cent of 9,169 isolates were resistant, whereas in 1975, 7.7 per cent of 7,817 isolates were resistant to the activity of gentamicin (x2 = 527, p 16 pglml) in 1975 was observed among Klebsiella species (20 per cent). Sixteen per cent of the Pseudomonas strains, 14 per cent of the Enterobacter strains, 12 per cent of the Proteus strains and 3 per cent of the Escherichia strains were also resistant by tube dilution to the activity of gentamicin. These results paralleled disc sensitivity studies with all clinical isolates. Bacteremic Infections Caused by Gentamicin-Resistant Gram-Negative Bacilli in 1974-1975. Epidemiology: During 1974-1975, 20 per cent of all nosocomial gram-negative bacteremias at the University of Virginia Hospital were caused by gentamicin-resistant
June 1977
The American Journal of Medicine
Volume 62
695
NOSOCOMIAL BLOOOSTREAM INFECTIONS-WERRANT
ET AL.
TotalCares Gentamicin Resistant Cares
r
I
JFMAMJJASONDlFMAMJJASOND
I
1974
1975
Figure 1. Emergence of gentamicin-resistance among nosocomial gramnegative rod bacteremias at the University of Virginia Hospital, total number of cases and gentamicin-resistant cases by month for 1974- 1975.
organisms. II, 1974, of 50 nosocomial gram-negative bacteremias (2.6/1,000 admissions) 10 were due to gentamicin-resistant organisms: and in 1975, of 114 bacteremias (5.6/1,000 admissions) 24 were due to gentamicin-resistant organisms. Patients who were in intensive care units accounted for 7 1 per cent (24 of 34) of the patients with gentamicin-resistant bacteremic infections. Ten infections eccurred in patients in the surgical intensive care unit, 11 in patients in the burn unit which opened in November 1974, two in patients in the medical acute care unit and one in a patient in the coronary care unit. When control patients who were “case-matched” in time (i.e., the next nosocomial gram-negative bacteremia in the hospital) were examined for location, only 22 per cent (seven of 32) were in intensive care units and none of the seven patients was in the same unit as their match (x2 = 13.8, p 32 pg/ml). Twelve of the 14 isolates tested were susceptible to netilmicin, whereas 11 of the 15 strains tested against sisomicin were susceptible, and only one of the 15 strains tested was susceptible to tobramycin. Clinical Experience with Amikacin. In 10 of the 34 bacteremic infections, the patients were treated with amikacin: three patients with surgical wound infections, two patients with burn wound infections, two with pneumonia, one with a urinary tract infection, one with acute leukemia and one with a craniotomy wound infection complicated by meningitis. Amikacin was administered intramuscularly or intravenously in a dose of 15 mglkglday for six to 20 days: the dosage was modified in patients with impaired renal function by following serum amikacin concentrations. Of 10 pa-
June 1977
The American Journal of Medicine
Volume 62
897
NOSOCOMIAL BLOODSTREAM INFECTIONS-GUERRANT
TABLE
Patients
III
ET AL.
with Gentamicin-Resistant
Bacteremia:
Age
(vr)
Case No.
and Sex
Underlying Diseases and/or Procedures
1 2
77, F 56, M
3
48, M
4
66, M
5
27, F
6
29, F
7
42, M
8
76, M
9
40, M
10 11
69, F 63, M
Asthma; pneumonia; respiratory failure Pelvic crush injury; exploratory laparotomy Mitral valve replacement; renal and respiratory failure Gastrointestinal hemorrhage; shock; respiratory failure; gangrene of leg; above the knee amputation Pancreatitis; choledocholithiasis cholecystectomy; renal failure, respiratory failure Abdominal trauma; fractured head of pancreas; exploratory laparotomysubtotal gastrectomy; respiratory failure 35% 3rd degree burn; renal and respiratory failure Pneumoconiosis; status postcholecystectomy Abdominal gun-shot wound; exploratory laparotomy-antrectomy and gastrojejunostomy; renal failure 26% 3rd degree burn; respiratory failure 70% 3rd degree burn; respiratory failure
44, F
30% 3rd degree burn; respiratory
12
48, M 26, M 89, F
16 17
60, F 39, F (a) (b)
18
73, M
19
84, M
20
J6, F
21
24, M
22 23 24 25
49, 25, 77, 55,
26
69, M
27
50. F
28
29, F
29 30
40. M 70, M
31 32
60, M 68, F
898
M M M M
June 1977
Acute myelomonocytic leukemia 50% 3rd degree burn Diabetes mellitus, ascending cholangitis; obstructive uropathy; pyelonephritis; nephrostomy Metastatic carcinoma of the cervix Renal transplant; diabetes mellitus; recurrent pulmonary emboli; bilateral femoral venous ligation Benign prostatic hypertrophy; transurethral resection of prostate; diabetes mellitus Perforated gallbladder; cholescystectomy; peritonitis; respiratory failure Diabetes mellitus; gangrene of leg; amputation of leg Depressed skull fracture; craniotomy and debridement 85% burn; respiratory failure 50% burn, respiratory failure Renal failure Gun-shot wound to throat; mediastinitis, renal and respiratory failure 45% 3rd degree burn; respiratory failure Congestive heart failure; respiratory failure; pleural effusion-chest tube Acute renal failure; pelvic abscess; respiratory failure; status postlaparotomy 51% 3rd degree burn Chronic obstructive pulmonary disease; respiratory failure; lymphoma 37% 3rd degree burn; respiratory failure Pulmonary emboli; respiraitory and renal failure; congestive heart failure
The American Journal of Medicine
1975
No. of Hospital Days Prior to Bacteremia
Source of Bacteremia
5 4
Respiratory Unknown
tract
Previous Gentamicin Therapy
Outcome
No Yes
Died Died
34
Surgical wound
Yes
Died
20
Surgical wound
Yes
Died
12
Unknown
Yes
Died
27
Urine
Yes
Survived
No
Died
9
Respiratory
tract
9
Urine
No
Survived
25
Surgical wound
Yes
Died
25 11
Respiratory tract Central venous pressure catheter
Yes No
Died Died
22 54 33 11 24
Respiratory Unknown Unknown Unknown Urine
No Yes No Yes Yes
Survived Died Died Survived Survived
16
Decubitus
Yes
Survived
14 31 4
Surgical wound Surgical wound Urine
No No No
Survived Survived Survived
Respiratory
Yes
Died
failure
(a) (b) 13 14 15
Jan. 1974-Dec.
Volume 82
7
tract
ulcer
tract
41
Surgical wound
Yes
Survived
6
Surgical wound
No
Survived
Unknown Unknown Wound infection Wound infection
Yes Yes Yes No
Died Died Died Died
Yes
Died
18
Central venous pressure catheter Surgical wound
NO
Died
25
Unknown
Yes
Died
IO 14
Burn wound Respiratory tract
No Yes
Died Survived
4 31
Burn wound Respiratory tract
No Yes
Died Died
12 60 42 46 4
NOSOCOMIAL
TABLE IV
BLOODSTREAM
INFECTIONS-GUERRANT
Aminoglycoside Resistance (>8 fig/ml) Among Clinical Isolates in 1975
Genus Klebsiella Enterobacter Escherichia Proteus Pseudomonas
No. 65 22 37 26 31
Gentamicin (%) 20 14 3 12 16
tients who were treated with amikacin, one died within 24 hours of receiving his initial amikacin dose. In one patient, who had the resistant Flavobacterium species (MIC >32 wg/ml), the organism appeared to clear from his bloodstream during amikacin therapy. In the remaining eight patients, rapid sterilization of the bloodstream and clinical improvement were demonstrated. Four patients survived to leave the hospital, and four died of their underlying diseases. The eventual mortality during hospitalization among these 10 patients who received amikacin (60 per cent) was not significantly different from the mortality in the remaining 24 episodes of gentamicin-resistant bacteremia (17/24, 7 1 per cent) and reflected the severe degree of underlying illness in all of these patients. All patients in this study were too ill to have full audiometric evaluation, but in a single patient treated with amikacin deafness developed after therapy. This patient had obstructive uropathy and a urinary tract infection, and had also received large doses of furosemide. The administration of amikacin was otherwise well tolerated. Two patients died with bacterial suprainfection, one with Pseudomonas pneumonia and another with Proteus sepsis, both of which were sensitive to gentamicin. COMMENTS The occurrence of nosocomial bacteremic infections caused by gentamicin-resistant gram negative bacilli in 1974-1975 paralleled the increased resistance to gentamicin observed in unselected clinical isolates from multiple sources at the University of Virginia Hospital between 1971 and 1975. Between 1971 and 1975, the percentage of resistant strains increased from less than 1 per cent to 7.7 per cent. During 1974-1975, 20 per cent of all nosocomial gram-negative bacteremias were caused by gentamicin-resistant organisms. The organisms that were most commonly gentamitin-resistant both in the unselected clinical isolates in 1975 and in the gram-negative bacteremias in 1974-l 975 were Klebsiella, Pseudomonas and Enterobacter strains. Of all gentamicin-resistant gram-negative bacteremias 48 per cent were Klebsiella, 15 per cent were Pseudomonas, and 12 per cent were Enterobacter. The relative incidence of these infections did
Amikacin (%)
Netilmicin (%)
3 0 0 4 10
3 0 3 19 26
ET AL.
-Sisomicin (%)
Tobramycin (%)
17 0 3 4 6
18 14 5 8 6
not increase during the study period, even though the incidence of bacteremic infections more than doubled (from 2.6 per thousand admissions in 1974 to 5.6 per thousand admissions in 1975), and the use of gentamicin was not restricted. Although others, too, have reported the emergence of nosocomial Klebsiella infections [3,4,10], some have attributed control of these infections to limitations on antibiotic usage [5,111. All 34 gentamicin-resistant bacteremic episodes occurred in patients who had been hospitalized from four to 60 days (median, 17 days). There were several risk factors that identified patients most likely to have bloodstream infections with gentamicin-resistant gram-negative organisms. These include the following: (1) All patients had severe underlying diseases including extensive burns, trauma, surgery, respiratory failure, renal failure or disseminated malignancies. (2) In 25 of the 32 patients (78 per cent) the gentamicin-resistant organism was isolated from an identifiable site prior to or concomitant with bloodstream seeding. These included skin (12 patients), respiratory tract (seven patients), urinary tract (four patients) and a central venous pressure catheter (two patients). (3) All but one of these patients had received antibiotics prior to the appearance of their gentamicin-resistant bacteremia. Although 19 of these patients had actually received gentamicin. 14 had received other antibiotics including cephalosporins, chloramphenicol and penicillins. (4) Over 70 per cent of these patients were hospitalized in intensive care units. These patients were more likely to be in intensive care units than patients with nosocomial bacteremia caused by gentamicin-sensitive strains. Furthermore, there appears to be a tendency toward a clustering of gentamicin-resistant bacteremias in time. Only two pairs of patients had common organisms while they were located in the same intensive care unit at the same time. Other temporal and spatial clustering also raises the possibility of spread of resistant organisms. Our attempts at in vitro transfer to gentamicin resistance to recipient Esch. coli have failed to date. The association of antibiotic-resistant nosocomial pathogens with the use of the antibiotic in the hospital at large has been observed by Bulger et al. [ 121. The
June 1977 The American Journal of Medlclne Volume62
899
NOSOCOMIAL
BLOODSTREAM
INFECTIONS-GUERRANT
ET AL.
occurrence of gentamicin-resistant bacteremia was associated with prior gentamicin usage in over half of our patients, thus suggesting the possibility that gentamicin-resistant organisms were selected from the patients’ own flora. However, 15 of the patients with gentamicin-resistant organisms had not received prior aminoglycosides. This observation suggests that the gentamicin-resistant organisms may have been transmitted to the patients by exposure to the hospital environment or personnel. Hands of personnel have been shown to be not only potential vehicles for gram-negative bacitli, but also potential reservoirs with bacterial multiplication as well [ 131. Additionally, the previous use of antibiotics in all but one of these patients may have contributed either by suppressing normal flora and thus normal resistance to the acquisition of new potential pathogens or by their own flora becoming resistant to gentamicin along with resistance to the antibiotics these patients received, as by a linked R factor-coded resistance pattern. As shown in our hospital and by others [ 141, amikacin was the most active aminoglycoside by weight against the gentamicin-resistant gram-negative isolates. It also proved effective in a limited clinical trial in the therapy of patients with bacteremia caused by the gentamicin-resistant strains. Toxicity was difficult to evaluate in these extremely sick patients; however, in one patient, who also received large doses of furosemide, there appeared to be a significant decrease in auditory function. In two other patients, suprainfections developed. Other studies have documented the potential efficacy of amikacin in the therapy of patients with serious gram-negative bacillary infections as well as with its ototoxicity [ 15,161. Amikacin is now considered the initial drug of choice in our hospital for the treatment of patients with nosocomial septicemia in intensive care units. This study documents the emergence of gentamitin-resistance as a difficult nosocomial problem. Because of the very limited number of alternative antibiotics, the problem of gentamicin-resistance must be
attacked at its source. There were significant associations of gentamicin-resistant bacteremias with (1) intensive care units, (2) generalized hospital use of gentamicin and (3) use of gentamicin or broad-spectrum antibiotics in the individual patient. Although amikacin appears to be an effective antibiotic at this time, the risk of additional resistance reemphasizes the importance of preventive measures. The potential for the development of amikacin resistance was demonstrated in a single patient receiving the drug because of gentamitin-resistant Klebsiella peritonitis. The patient was in renal failure and was undergoing peritoneal dialysis. Following a single injection of amikacin, signs of peritonitis subsided and the patient became afebrile. The serum amikacin concentration was 10 Kg/ml four days after the drug was given. The organism, however, was repeatedly isolated from the peritoneal fluid over eight days. The MIC and minimum bactericidal concentration (MBC) of amikacin for the initial isolate were 0.5 pg/ml and 2 pg/ml, respectively, but the MIC and MBC had both increased to 8 pg/ml for the Klebsiella isolated on the eighth day. A reasonable approach to this problem would include (1) judicious use of broad-spectrum antibiotics, especially the aminoglycosides (the limitation of widespread usage of gentamicin and other antibiotics to those patients who have good indications for these drugs) and (2) initial use of amikacin for septicemia in patients with known foci of gentamicin-resistant organisms or those in whom sepsis develops during their stay in intensive care units. The two pairs of patients in this study with common gentamicin-resistant organisms in common locations suggest the possibility of spread within the intensive care unit setting. Further studies of this latter potential for spread of resistant organisms are indicated and are currently in progress. ACKNOWLEDGMENT We wish to express our thanks to Dr. C. M. Russell, S. Voth and K. Courtney for their technical assistance.
REFERENCES 1.
2. 3.
4.
5.
900
Finland M: Changing patterns of susceptibility of common bacterial pathogens to antimicrobial agents. Ann Intern Med 76: 1009,1972. Wolff SM. Bennett JV: Gram-negative rod bacteremia (editorial). N Engl J Med 291: 733, 1974. Davis TJ, Matsen JM: Prevalence and characteristics of Klebsiella species. Relation to association with a hospital environment. J Infect Dis 130: 402, 1974. Martin CM, lkari NS, Zimmerman J, et al.: A virulent nosocomial Klebsiella with a transferable R factor for gentamicin: emergence and suppression. J Infect Dis 124 (suppl): 24, 1971. Price DJE, Sleigh JD: Control of infection due to Klebsiella
June 1977
The American
Journal of Medlcine
Volume 62
6.
7.
8.
9.
aerogenes in a neurosurgical unit by withdrawal of all antibiotics. Lancet 2: 1213, 1970. MacLowry JD, Jaqua MJ, Selepak ST: Detailed methodology and implementation of a semi-automated serial dilution microtechnique for antimicrobial susceptibility testing. Appl Microbial 20: 46, 1970. Wenzel RP, Osterman C, Hunting K. et al.: Hospital acquired infection. I. Surveillance in a university hospital. Am J Epidemiol 103: 251. 1976. Edwards FR, Ewing WH: Identification of Enterobacteriaceae, 3rd ed. Minneapolis, Minn., Burgess Publishing Co., 1972. 8auer AW, Kirby WMM, Sherris JC, et al.: Antibiotic suscep-
NOSOCOMIAL
10.
11.
12.
tibility testing by a standardized single disc method. Am J Clin Pathol 45: 493, 1966 Selden R. Lee S, Wang WLL, et al.: Nosocomial Klebsiella infections. Intestinal colonization as a reservoir. Ann Intern Med 74: 657, 1971. Noriega ER, Leibowitz RE, Richmond AS, et al.: Nosocomial infection caused by gentamicin-resistant, streptomycinsensitive Klebsiella. J Infect Dis 131: 545, 1975. Bulger RJ, Larson E, Sherris JC: Decreased incidences of resistance to antimicrobial agents among Escherichia coli and Klebsiella-Enterobacter. Observations in a university hospital over a lo-year period. Ann Intern Med 72: 65, 1970.
13.
14.
15.
16.
June 1977
BLOODSTREAM
INFECTIONS-GUERRANT
ET AL.
Knittle MA, Eitzman DV, Baer H: Role of hand contamination of personnel in the epidemiology of gram-negative nosocomial infections. J Pediatr 86: 433, 1975. Price KE, Pursiano TA, DeFuria MD, et al.: Activity of BB-K8 (amikacin) against clinical isolates resistant to one or more aminoglycoside antibiotics. Antimicrob Agents Chemother 5: 143, 1974. Tally FP, Louie TJ, Weinstein WM, et al.: Amikacin therapy for severe gram-negative sepsis. Ann Intern Med 83: 484, 1975. Meyer RD. Lewis RP, Carmalt ED, et al.: Amikacin therapy for serious gram-negative bacillary infections. Ann Intern Med 83: 790, 1975.
The American Journal of Medicine
Volume 62
901
R. L. GUERRANT, M.D. L. J. STRAUSBAUGH,
M.D.
R. P. WENZEL, M.D. B. H. HAMORY, M. A. SANDE,
M.D. M.D.
Charlottesville, Virginia
From the Department of Internal Medicine, University of Virginia School bf Medicine, Charlottesville, Virginia 2290 1. This studywas presented at the U.S. Amikacin Symposium, Unlversity of California Medical School, Los Angeles, California, November 9-10. 1976. Requests for reprints should be addressd to Dr. R. L. Guerrant, University of Virginia School of Medicine, Box 305, Charlottesville, Virginia 22901.
094
June 1977
Gentamicin resistance has emerged since 1971 among gram-negatlve bacilli isolated at the University of Virglnla Hospital. 019,169 gram-negative bacilli isolated in 1971,0.6 per cent were resistant to gentamicin by disc sensitivity testing. of 7,617 isolates in 1975, 7.7 per cent were resistant. Approximately 20 per cent of the Klebsiellae had a minimum inhibitory concentration (MC) 116 pg/ml of gentamicin. Since 1974, gentamicin-resistant gram-negative bacilli have accounted for 20 per cent of nosocomial bacteremias. In 1974-1975, 34 episodes of gentamicln-resistant bacteremia occurred. All were in patients with severe underlying diseases who had been hospitalized for longer than four days; 24 (71 per cent) occurred in patients in intensive care units. The organisms isolated were Klebsiella pneumoniae (12 cases), Klebsietla sp. (five cases), Pseudomonas aeruginosa (five cases), Enterobacter aerogenes (three cases), Serratia marcescens (three cases) and others (seven cases). Ail but one of the bacteremic patients had received prior antibiotics, and 19 of 34 episodes were preceded by gentamicin therapy. Nine patients with bacteremia caused by the gentamicin-resistant strains received one to three weeks of amikacin therapy. All showed clinical improvement and the organism cleared from their bloodstreams; in one patient clinical deafness developed; in two patients bacterial suprainfections developed, and five patients subsequently died of other causes during their hospitalization. The introduction of a new antibiotic into clinical medicine is often followed by the emergence of resistant organisms which eventually limit its usefulness [ 11. Antibiotic resistance has been especially common among people with aerobic gram-negative bacilli, often acquired in hospitals [2-51. Gentamicin sulfate was added to the formulary of the University of Virginia Hospital in 1969, and it rapidly replaced kanamycin as the principal antimicrobial agent for treating patients with life-threatening infections caused by gram-negative enteric bacilli. Bacteremia caused by gentamicin-resistant organisms first appeared in our hospital in March 1974; subsequently, it became a major clinical problem. In this report we describe (1) the emergence
The American Journal of Medlclne
VOlUme 62
NOSOCOMIAL
of gentamicin-resistance
among gram-negative bacilli
isolated
of Virginia
at the University
Hospital
1971 and 1975; (2) the epidemiologic,
TABLE I
between
microbiologic
and clinical characteristics of 34 bacteremic comial infections caused by gentamicin-resistant ganisms in 1974 and 1975; and (3) the therapeutic of amikacin in this setting.
nosoorvalue
MATERIALS AND METHODS In Vitro SusceptibilityStudies. A total of 118 gram-negative bacilli were randomly obtained after speciation from the clinical microbiology laboratory of the University of Virginia Hospital in 1971, and 181 similar isolates were obtained in 1975. Seventeen strains of gentamicin-resistant organisms obtained from blood cultures of patients with bacteremic infections in 1974-1975 were tested against these same aminoglycosides. The minimum inhibitory concentrations (MIC) of gentamicin (Garamycine, Schering Corporation, Kenilworth, N.J.), amikacin (Amikine, Bristol Laboratories, Syracuse, N.Y.), sisomicin (Schering Corporation, Kenilworth, N.J.), tobramycin (Nebcin-R@, Eli Lilly & Co., Indianapolis, Ind.) and netilmicin (Schering Corporation, Kenilworth, N.J.) were determined in beef heart infusion broth (Difco, Detroit, Mich.) using a serial microdilution technic [6]. The MIC was defined as the lowest concentration of drug that inhibited growth following 24 hours of incubation. Strains with an MIC of 8 pg/ml or less were considered to be “sensitive” to the aminoglycoside in question, whereas strains with an MIC greater than 8 pglml were considered to be “resistant.” A further review of all Kirby-Bauer disc sensitivity testing carried out on clinical gram-negative bacillary isolates in the hospital bacteriology laboratory was made for 1971 and 1975.
Appearance of Gentamicin-Resistant Bacteremia in 1974-1975. Patients with bacteremia caused by gentamitin-resistant gram-negative bacilli were identified by (1) the ongoing surveillance system of the hospital epidemiology unit [7] and (2) reviewing the records of all patients with positive blood cultures in the hospital’s microbiology laboratory. These charts were reviewed for the patient’s age, sex, location in the hospital, date of bacteremia, diagnosis, number of days in the hospital prior to the onset of bacteremia, antibiotic therapy given prior to the development of bacteremia, potential sources of bacteremia, operations and procedures, therapy and outcome. All patients had multiple positive blood cultures for gentamicin-resistant gram-negative bacilli, and they were treated for clinically significant infections. In addition, the number and dates of all “nosocomial” bacteremias were determined by an ongoing surveillance system [7]. Nosocomial infections are defined as those for which there is no clinical evidence at the time of hospital admission. Isolates from blood and other sites were identified in the clinical microbiology laboratory using standard methods [8]. Antibiotic susceptibility tests on these isolates were performed with the Kirby-Bauer disc diffusion method using carbenicillin, ampicillin, benzyl penicillin, methicillin, cephalothin, tetracycline, chloramphenicol, streptomycin, vancomycin, kanamycin and gentamicin discs [9]. An organism
BLOODSTREAM
INFECTIONS-GUERRANT
Gentamicin Resistance (MIC 316 pg/ml) Among Clinical Isolates at the University Virginia Hospital in 1971 and 1975 1971
Genus Klebslella Enterobacter Escherichia Proteus Pseudomonas
ET AL.
Strains Tested (no.) 25 18 25 25 25
of
1975”
Resistant (%) 4 0 0 0 0
Strains Tested (no.) 65 22 37 26 31
Resistant (%) 20 14 3 12 16
*Of 7,817 gram-negative bacilli isolated from clinical specimens in 1975, 7.7 per cent were resistant to gentamicin by disc.
was considered to be resistant to gentamicin if the zone of inhibition was less than 12 mm. Eleven of the 12 strains of Klebsiella pneumoniae were tested against types 1, 2,3.4, 5, 6 and 21 antiserums for the quellung reaction. Therapywith Amikacin. Ten of the patientswith nosocomial gram-negative bacillary septicemia received amikacin following isolation of the organism and proof of gentamicinresistance. The drug was administered at a dose of 7.5 mg/kg twice a day intramuscularly or intravenously. Patients were monitored to determine the effectiveness of therapy (blood cultures, temperature and survival) and toxicity (renal, liver and neurologic function), if any.
RESULTS Emergence of Gentamicin-Resistant Organisms 1971-1975. When compared with clinical isolates from 1971, isolates of gram-negative bacilli from 1975 demonstrated a strikingly increased resistance to gentamicin (Table I). A review of disc sensitivity studies on all aerobic gram-negative bacilli isolated from cfinical specimens in 1971 revealed that less than 1 per cent of 9,169 isolates were resistant, whereas in 1975, 7.7 per cent of 7,817 isolates were resistant to the activity of gentamicin (x2 = 527, p 16 pglml) in 1975 was observed among Klebsiella species (20 per cent). Sixteen per cent of the Pseudomonas strains, 14 per cent of the Enterobacter strains, 12 per cent of the Proteus strains and 3 per cent of the Escherichia strains were also resistant by tube dilution to the activity of gentamicin. These results paralleled disc sensitivity studies with all clinical isolates. Bacteremic Infections Caused by Gentamicin-Resistant Gram-Negative Bacilli in 1974-1975. Epidemiology: During 1974-1975, 20 per cent of all nosocomial gram-negative bacteremias at the University of Virginia Hospital were caused by gentamicin-resistant
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TotalCares Gentamicin Resistant Cares
r
I
JFMAMJJASONDlFMAMJJASOND
I
1974
1975
Figure 1. Emergence of gentamicin-resistance among nosocomial gramnegative rod bacteremias at the University of Virginia Hospital, total number of cases and gentamicin-resistant cases by month for 1974- 1975.
organisms. II, 1974, of 50 nosocomial gram-negative bacteremias (2.6/1,000 admissions) 10 were due to gentamicin-resistant organisms: and in 1975, of 114 bacteremias (5.6/1,000 admissions) 24 were due to gentamicin-resistant organisms. Patients who were in intensive care units accounted for 7 1 per cent (24 of 34) of the patients with gentamicin-resistant bacteremic infections. Ten infections eccurred in patients in the surgical intensive care unit, 11 in patients in the burn unit which opened in November 1974, two in patients in the medical acute care unit and one in a patient in the coronary care unit. When control patients who were “case-matched” in time (i.e., the next nosocomial gram-negative bacteremia in the hospital) were examined for location, only 22 per cent (seven of 32) were in intensive care units and none of the seven patients was in the same unit as their match (x2 = 13.8, p 32 pg/ml). Twelve of the 14 isolates tested were susceptible to netilmicin, whereas 11 of the 15 strains tested against sisomicin were susceptible, and only one of the 15 strains tested was susceptible to tobramycin. Clinical Experience with Amikacin. In 10 of the 34 bacteremic infections, the patients were treated with amikacin: three patients with surgical wound infections, two patients with burn wound infections, two with pneumonia, one with a urinary tract infection, one with acute leukemia and one with a craniotomy wound infection complicated by meningitis. Amikacin was administered intramuscularly or intravenously in a dose of 15 mglkglday for six to 20 days: the dosage was modified in patients with impaired renal function by following serum amikacin concentrations. Of 10 pa-
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TABLE
Patients
III
ET AL.
with Gentamicin-Resistant
Bacteremia:
Age
(vr)
Case No.
and Sex
Underlying Diseases and/or Procedures
1 2
77, F 56, M
3
48, M
4
66, M
5
27, F
6
29, F
7
42, M
8
76, M
9
40, M
10 11
69, F 63, M
Asthma; pneumonia; respiratory failure Pelvic crush injury; exploratory laparotomy Mitral valve replacement; renal and respiratory failure Gastrointestinal hemorrhage; shock; respiratory failure; gangrene of leg; above the knee amputation Pancreatitis; choledocholithiasis cholecystectomy; renal failure, respiratory failure Abdominal trauma; fractured head of pancreas; exploratory laparotomysubtotal gastrectomy; respiratory failure 35% 3rd degree burn; renal and respiratory failure Pneumoconiosis; status postcholecystectomy Abdominal gun-shot wound; exploratory laparotomy-antrectomy and gastrojejunostomy; renal failure 26% 3rd degree burn; respiratory failure 70% 3rd degree burn; respiratory failure
44, F
30% 3rd degree burn; respiratory
12
48, M 26, M 89, F
16 17
60, F 39, F (a) (b)
18
73, M
19
84, M
20
J6, F
21
24, M
22 23 24 25
49, 25, 77, 55,
26
69, M
27
50. F
28
29, F
29 30
40. M 70, M
31 32
60, M 68, F
898
M M M M
June 1977
Acute myelomonocytic leukemia 50% 3rd degree burn Diabetes mellitus, ascending cholangitis; obstructive uropathy; pyelonephritis; nephrostomy Metastatic carcinoma of the cervix Renal transplant; diabetes mellitus; recurrent pulmonary emboli; bilateral femoral venous ligation Benign prostatic hypertrophy; transurethral resection of prostate; diabetes mellitus Perforated gallbladder; cholescystectomy; peritonitis; respiratory failure Diabetes mellitus; gangrene of leg; amputation of leg Depressed skull fracture; craniotomy and debridement 85% burn; respiratory failure 50% burn, respiratory failure Renal failure Gun-shot wound to throat; mediastinitis, renal and respiratory failure 45% 3rd degree burn; respiratory failure Congestive heart failure; respiratory failure; pleural effusion-chest tube Acute renal failure; pelvic abscess; respiratory failure; status postlaparotomy 51% 3rd degree burn Chronic obstructive pulmonary disease; respiratory failure; lymphoma 37% 3rd degree burn; respiratory failure Pulmonary emboli; respiraitory and renal failure; congestive heart failure
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1975
No. of Hospital Days Prior to Bacteremia
Source of Bacteremia
5 4
Respiratory Unknown
tract
Previous Gentamicin Therapy
Outcome
No Yes
Died Died
34
Surgical wound
Yes
Died
20
Surgical wound
Yes
Died
12
Unknown
Yes
Died
27
Urine
Yes
Survived
No
Died
9
Respiratory
tract
9
Urine
No
Survived
25
Surgical wound
Yes
Died
25 11
Respiratory tract Central venous pressure catheter
Yes No
Died Died
22 54 33 11 24
Respiratory Unknown Unknown Unknown Urine
No Yes No Yes Yes
Survived Died Died Survived Survived
16
Decubitus
Yes
Survived
14 31 4
Surgical wound Surgical wound Urine
No No No
Survived Survived Survived
Respiratory
Yes
Died
failure
(a) (b) 13 14 15
Jan. 1974-Dec.
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tract
ulcer
tract
41
Surgical wound
Yes
Survived
6
Surgical wound
No
Survived
Unknown Unknown Wound infection Wound infection
Yes Yes Yes No
Died Died Died Died
Yes
Died
18
Central venous pressure catheter Surgical wound
NO
Died
25
Unknown
Yes
Died
IO 14
Burn wound Respiratory tract
No Yes
Died Survived
4 31
Burn wound Respiratory tract
No Yes
Died Died
12 60 42 46 4
NOSOCOMIAL
TABLE IV
BLOODSTREAM
INFECTIONS-GUERRANT
Aminoglycoside Resistance (>8 fig/ml) Among Clinical Isolates in 1975
Genus Klebsiella Enterobacter Escherichia Proteus Pseudomonas
No. 65 22 37 26 31
Gentamicin (%) 20 14 3 12 16
tients who were treated with amikacin, one died within 24 hours of receiving his initial amikacin dose. In one patient, who had the resistant Flavobacterium species (MIC >32 wg/ml), the organism appeared to clear from his bloodstream during amikacin therapy. In the remaining eight patients, rapid sterilization of the bloodstream and clinical improvement were demonstrated. Four patients survived to leave the hospital, and four died of their underlying diseases. The eventual mortality during hospitalization among these 10 patients who received amikacin (60 per cent) was not significantly different from the mortality in the remaining 24 episodes of gentamicin-resistant bacteremia (17/24, 7 1 per cent) and reflected the severe degree of underlying illness in all of these patients. All patients in this study were too ill to have full audiometric evaluation, but in a single patient treated with amikacin deafness developed after therapy. This patient had obstructive uropathy and a urinary tract infection, and had also received large doses of furosemide. The administration of amikacin was otherwise well tolerated. Two patients died with bacterial suprainfection, one with Pseudomonas pneumonia and another with Proteus sepsis, both of which were sensitive to gentamicin. COMMENTS The occurrence of nosocomial bacteremic infections caused by gentamicin-resistant gram negative bacilli in 1974-1975 paralleled the increased resistance to gentamicin observed in unselected clinical isolates from multiple sources at the University of Virginia Hospital between 1971 and 1975. Between 1971 and 1975, the percentage of resistant strains increased from less than 1 per cent to 7.7 per cent. During 1974-1975, 20 per cent of all nosocomial gram-negative bacteremias were caused by gentamicin-resistant organisms. The organisms that were most commonly gentamitin-resistant both in the unselected clinical isolates in 1975 and in the gram-negative bacteremias in 1974-l 975 were Klebsiella, Pseudomonas and Enterobacter strains. Of all gentamicin-resistant gram-negative bacteremias 48 per cent were Klebsiella, 15 per cent were Pseudomonas, and 12 per cent were Enterobacter. The relative incidence of these infections did
Amikacin (%)
Netilmicin (%)
3 0 0 4 10
3 0 3 19 26
ET AL.
-Sisomicin (%)
Tobramycin (%)
17 0 3 4 6
18 14 5 8 6
not increase during the study period, even though the incidence of bacteremic infections more than doubled (from 2.6 per thousand admissions in 1974 to 5.6 per thousand admissions in 1975), and the use of gentamicin was not restricted. Although others, too, have reported the emergence of nosocomial Klebsiella infections [3,4,10], some have attributed control of these infections to limitations on antibiotic usage [5,111. All 34 gentamicin-resistant bacteremic episodes occurred in patients who had been hospitalized from four to 60 days (median, 17 days). There were several risk factors that identified patients most likely to have bloodstream infections with gentamicin-resistant gram-negative organisms. These include the following: (1) All patients had severe underlying diseases including extensive burns, trauma, surgery, respiratory failure, renal failure or disseminated malignancies. (2) In 25 of the 32 patients (78 per cent) the gentamicin-resistant organism was isolated from an identifiable site prior to or concomitant with bloodstream seeding. These included skin (12 patients), respiratory tract (seven patients), urinary tract (four patients) and a central venous pressure catheter (two patients). (3) All but one of these patients had received antibiotics prior to the appearance of their gentamicin-resistant bacteremia. Although 19 of these patients had actually received gentamicin. 14 had received other antibiotics including cephalosporins, chloramphenicol and penicillins. (4) Over 70 per cent of these patients were hospitalized in intensive care units. These patients were more likely to be in intensive care units than patients with nosocomial bacteremia caused by gentamicin-sensitive strains. Furthermore, there appears to be a tendency toward a clustering of gentamicin-resistant bacteremias in time. Only two pairs of patients had common organisms while they were located in the same intensive care unit at the same time. Other temporal and spatial clustering also raises the possibility of spread of resistant organisms. Our attempts at in vitro transfer to gentamicin resistance to recipient Esch. coli have failed to date. The association of antibiotic-resistant nosocomial pathogens with the use of the antibiotic in the hospital at large has been observed by Bulger et al. [ 121. The
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occurrence of gentamicin-resistant bacteremia was associated with prior gentamicin usage in over half of our patients, thus suggesting the possibility that gentamicin-resistant organisms were selected from the patients’ own flora. However, 15 of the patients with gentamicin-resistant organisms had not received prior aminoglycosides. This observation suggests that the gentamicin-resistant organisms may have been transmitted to the patients by exposure to the hospital environment or personnel. Hands of personnel have been shown to be not only potential vehicles for gram-negative bacitli, but also potential reservoirs with bacterial multiplication as well [ 131. Additionally, the previous use of antibiotics in all but one of these patients may have contributed either by suppressing normal flora and thus normal resistance to the acquisition of new potential pathogens or by their own flora becoming resistant to gentamicin along with resistance to the antibiotics these patients received, as by a linked R factor-coded resistance pattern. As shown in our hospital and by others [ 141, amikacin was the most active aminoglycoside by weight against the gentamicin-resistant gram-negative isolates. It also proved effective in a limited clinical trial in the therapy of patients with bacteremia caused by the gentamicin-resistant strains. Toxicity was difficult to evaluate in these extremely sick patients; however, in one patient, who also received large doses of furosemide, there appeared to be a significant decrease in auditory function. In two other patients, suprainfections developed. Other studies have documented the potential efficacy of amikacin in the therapy of patients with serious gram-negative bacillary infections as well as with its ototoxicity [ 15,161. Amikacin is now considered the initial drug of choice in our hospital for the treatment of patients with nosocomial septicemia in intensive care units. This study documents the emergence of gentamitin-resistance as a difficult nosocomial problem. Because of the very limited number of alternative antibiotics, the problem of gentamicin-resistance must be
attacked at its source. There were significant associations of gentamicin-resistant bacteremias with (1) intensive care units, (2) generalized hospital use of gentamicin and (3) use of gentamicin or broad-spectrum antibiotics in the individual patient. Although amikacin appears to be an effective antibiotic at this time, the risk of additional resistance reemphasizes the importance of preventive measures. The potential for the development of amikacin resistance was demonstrated in a single patient receiving the drug because of gentamitin-resistant Klebsiella peritonitis. The patient was in renal failure and was undergoing peritoneal dialysis. Following a single injection of amikacin, signs of peritonitis subsided and the patient became afebrile. The serum amikacin concentration was 10 Kg/ml four days after the drug was given. The organism, however, was repeatedly isolated from the peritoneal fluid over eight days. The MIC and minimum bactericidal concentration (MBC) of amikacin for the initial isolate were 0.5 pg/ml and 2 pg/ml, respectively, but the MIC and MBC had both increased to 8 pg/ml for the Klebsiella isolated on the eighth day. A reasonable approach to this problem would include (1) judicious use of broad-spectrum antibiotics, especially the aminoglycosides (the limitation of widespread usage of gentamicin and other antibiotics to those patients who have good indications for these drugs) and (2) initial use of amikacin for septicemia in patients with known foci of gentamicin-resistant organisms or those in whom sepsis develops during their stay in intensive care units. The two pairs of patients in this study with common gentamicin-resistant organisms in common locations suggest the possibility of spread within the intensive care unit setting. Further studies of this latter potential for spread of resistant organisms are indicated and are currently in progress. ACKNOWLEDGMENT We wish to express our thanks to Dr. C. M. Russell, S. Voth and K. Courtney for their technical assistance.
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2. 3.
4.
5.
900
Finland M: Changing patterns of susceptibility of common bacterial pathogens to antimicrobial agents. Ann Intern Med 76: 1009,1972. Wolff SM. Bennett JV: Gram-negative rod bacteremia (editorial). N Engl J Med 291: 733, 1974. Davis TJ, Matsen JM: Prevalence and characteristics of Klebsiella species. Relation to association with a hospital environment. J Infect Dis 130: 402, 1974. Martin CM, lkari NS, Zimmerman J, et al.: A virulent nosocomial Klebsiella with a transferable R factor for gentamicin: emergence and suppression. J Infect Dis 124 (suppl): 24, 1971. Price DJE, Sleigh JD: Control of infection due to Klebsiella
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aerogenes in a neurosurgical unit by withdrawal of all antibiotics. Lancet 2: 1213, 1970. MacLowry JD, Jaqua MJ, Selepak ST: Detailed methodology and implementation of a semi-automated serial dilution microtechnique for antimicrobial susceptibility testing. Appl Microbial 20: 46, 1970. Wenzel RP, Osterman C, Hunting K. et al.: Hospital acquired infection. I. Surveillance in a university hospital. Am J Epidemiol 103: 251. 1976. Edwards FR, Ewing WH: Identification of Enterobacteriaceae, 3rd ed. Minneapolis, Minn., Burgess Publishing Co., 1972. 8auer AW, Kirby WMM, Sherris JC, et al.: Antibiotic suscep-
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tibility testing by a standardized single disc method. Am J Clin Pathol 45: 493, 1966 Selden R. Lee S, Wang WLL, et al.: Nosocomial Klebsiella infections. Intestinal colonization as a reservoir. Ann Intern Med 74: 657, 1971. Noriega ER, Leibowitz RE, Richmond AS, et al.: Nosocomial infection caused by gentamicin-resistant, streptomycinsensitive Klebsiella. J Infect Dis 131: 545, 1975. Bulger RJ, Larson E, Sherris JC: Decreased incidences of resistance to antimicrobial agents among Escherichia coli and Klebsiella-Enterobacter. Observations in a university hospital over a lo-year period. Ann Intern Med 72: 65, 1970.
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Knittle MA, Eitzman DV, Baer H: Role of hand contamination of personnel in the epidemiology of gram-negative nosocomial infections. J Pediatr 86: 433, 1975. Price KE, Pursiano TA, DeFuria MD, et al.: Activity of BB-K8 (amikacin) against clinical isolates resistant to one or more aminoglycoside antibiotics. Antimicrob Agents Chemother 5: 143, 1974. Tally FP, Louie TJ, Weinstein WM, et al.: Amikacin therapy for severe gram-negative sepsis. Ann Intern Med 83: 484, 1975. Meyer RD. Lewis RP, Carmalt ED, et al.: Amikacin therapy for serious gram-negative bacillary infections. Ann Intern Med 83: 790, 1975.
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