Journal of Infection (1992) 25, 2II-214
CASE REPORT Metronidazole-resistant
Bacteroidesfragilis
wound infection
M. A. T. O ' D o n o g h u e , J. P o t t e r a n d K. D. A l l e n *
Microbiology Department, Whiston Hospital, Prescot, Merseyside L35 5DR, U.K. Accepted for publication I9 December I99I Summary We report the isolation of metronidazole-resistant Bacteroidesfragilis from a postoperative wound abscess in a 72-year-old woman who had not been treated with metronidazole during the preceding 9 months. The case illustrates the need for caution when identifying anaerobes on the basis of metronidazole sensitivity.
Introduction Metronidazole-resistance in Bacteroidesfragilis was first described in the U . K . in I 9 7 8 . 1 Several reports noted the emergence of metronidazole-resistant anaerobes during long-term metronidazole therapy (e.g. I7 days, 2 27 days, z and 3 yearsX) • However, metronidazole resistance is not often reported. As all aerobic organisms are resistant to metronidazole and anaerobes are usually sensitive, this property is used to facilitate the detection of anaerobes in mixed cultures. 4 A 5 #g metronidazole disc is placed on the main inoculum and, after anaerobic incubation, a zone around the metronidazole disc indicates the presence of anaerobes. Absence of a zone may be interpreted as absence of anaerobes. Metronidazole-resistant anaerobes may therefore pass unrecognised in mixed cultures and consequently their true incidence may be underestimated. We report the case of a patient with a post-operative wound abscess from which was isolated a strain of B.fragilis resistant to metronidazole. T h e patient had not received any recent antimicrobial chemotherapy.
Case report A previously healthy 72-year-old woman presented in June I99O with a weeklong history of jaundice and abdominal pain. An initial diagnosis of acute cholecystitis was made and she improved rapidly on intravenous cefuroxime (75o mg 8 hourly) and metronidazole (5oo mg 8 hourly). Five days later, however, her condition suddenly deteriorated. On examination the patient's temperature was 38"5 °C, her pulse rate was IOO beats/min and regular and the blood pressure was IOO/6O m m H g . H e r abdomen was distended with marked tenderness and guarding in the left iliac fossa. Laboratory testing revealed a haemoglobin of IO'9 g/dl with a W B C count * Author to whom correspondence should be sent. oi63-4453/92/o5o21I +04 $08.00/0
© I992 The British Society for the Study of Infection
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M.A.T. 0'DONOGHUE
ET AL.
of 28"6 x lO9/1. Serum amylase was 20 IU/1. An abdominal X-ray showed dilated loops of small bowel with air under the diaphragm. At laparotomy, a diagnosis of peritonitis secondary to a perforated diverticulum was made and a transverse colostomy performed. Intravenous cefuroxime and metronidazole were continued for 3 weeks. Before her discharge from hospital at the end of July, a barium enema showed the pelvic colon to be severely diseased. T h e patient was therefore readmitted IO weeks later for an elective sigmoid colectomy. She was allowed h o m e after 4 weeks, her post-operative recovery having been complicated by a chest infection which responded to treatment with oral ampicillin. D u r i n g this admission, her w o u n d discharged small amounts of serous fluid, culture of which yielded Streptococcus milleri, coliforms and Bacteroides sp. the last being sensitive to metronidazole. N o additional antibiotics were prescribed. Five m o n t h s later the patient was admitted a third time. Closure of her colostomy was performed without antibiotic prophylaxis and she was discharged h o m e r r days later after an uneventful recovery. D u r i n g this admission she received no antibiotics. Five days after her discharge, however, she presented to the Accident and Emergency D e p a r t m e n t complaining of a purulent discharge from her colostomy wound. On examination she appeared well and was apyrexial. Abdominal examination revealed a 3 x 2 cm abscess at t h e old colostomy site which was discharging purulent blood-stained material. T h e pus yielded a coliform sensitive to ampicillin, augmentin, ciprofloxacin, co-trimoxazole, cefuroxime, gentamicin and piperacillin and a / ? haemolytic Streptococcus sp. (which failed to group using the Wellcome Streptex kit) sensitive to penicillin, ampicillin, augmentin and erythromycin. F r o m the anaerobic neomycin blood agar plate a third colony type became apparent after 48 h. It failed to grow aerobically and, although colonial morphology was suggestive of a Bacteroides sp, no zone appeared around the 2"5 #g metronidazole disc. Subcultures of this colony onto blood agar plates incubated aerobically and anaerobically confirmed that the organism was an obligate anaerobe. Antibiotic disc susceptibility testing showed that it was resistant to metronidazole, penicillin and erythromycin but sensitive to amoxycillin-clavulanic acid, cefoxitin, clindamycin and chloramphenicol. T h e anaerobic Gram-negative bacillus was subsequently identified using the anaerobic A P I system (Bio-M6rieux, France) as Bacteroides fragilis. T h e M I C of metronidazole was determined by using Columbia agar base supplemented with 5 % fresh horse blood with a range of metronidazole concentrations (from 32 # g / m l to o.o6/zg/ml) as described by the Working Party of the British Society for Antimicrobial Chemotherapy. 5 Bacteroides fragilis N C T C 9343 was used as the control. Plates were incubated anaerobically at 37 °C for 48 h. T h e M I C of metronidazole for the patient's isolate was r6 #g/1. Metronidazole resistance was confirmed by the Public Health Laboratory at L u t o n and Dunstable Hospital using 5 #g and 5o #g metronidazole discs. Amoxycillin-clavulanic acid was c o m m e n c e d after the specimen of pus had been obtained. T h e patient was then discharged. One week later the w o u n d was healing well and a further swab did not yield anaerobes. Amoxycillinclavulanic acid was discontinued after I4 days. T h e patient remains well.
Metronidazole-resistant Bacteroides sp.
2 I3
Discussion
A l t h o u g h metronidazole has been in use since the late I95os metronidazole resistance a m o n g anaerobes, including Bacteroides spp., is still u n c o m m o n . T h e r e have been several i n d e p e n d e n t l y confirmed reports of stable metronidazole resistance in B. fragilis 1' 6.7 and a few u n c o n f i r m e d reports of r e d u c e d metronidazole sensitivity in B . f r a g i l i s strains, s-l° Resistance to metronidazole was not d e m o n s t r a t e d in any of the 651 B. fragilis group isolates tested in the U . K . in I987 although slightly r e d u c e d sensitivity was d e m o n s t r a t e d in five o f these strains (less than 1%).11 A s t u d y in the U . S . A . also f o u n d no evidence of metronidazole resistance in 5o6 strains of B . f r a g i l i s tested in I987 .12 In France, metronidazole M I C s greater than 9 rag/1 were only o b s e r v e d in two o f 3o0 strains of B . f r a g i l i s 1~ tested b e t w e e n I987 and I988, M a n y o f the patients from w h o m metronidazole-resistant Bacteroides sp. have been r e p o r t e d had been receiving metronidazole for comparatively long periods of time. 1-3 O u r patient had had metronidazole for 26 days during her initial stay in hospital b u t had not received any in the 9 m o n t h s before the isolation o f this metronidazole-resistant organism. In the intervening period Bacteroides sp. apparently sensitive to metronidazole, had been isolated from w o u n d swabs on at least one occasion. U n f o r t u n a t e l y , this strain is no longer available in the laboratory and it is impossible to establish w h e t h e r the metronidazole-sensifive and resistant Bacteroides spp. were of the same strain in which resistance determinants had developed. It is recognised, however, that metronidazole-resistant strains of Bacteroides sp. can be isolated from patients w h o have never received metronidazole. 1~ T h i s case demonstrates the need for caution w h e n using metronidazole discs to flag up anaerobes. A l t h o u g h metronidazole resistance is rare it does occur and appears to be b e c o m i n g m o r e c o m m o n in certain E u r o p e a n countries, e.g. Spain. 1° It is important therefore not to exclude the presence of an obligate anaerobe p u r e l y on the basis o f resistance to a metronidazole disc. Awareness o f the existence of such isolates will help to establish the true incidence of metronidazole-resistant anaerobes. (The authors wish to thank Mrs Susan Morgan for secretarial assistance in the preparation of this paper.) References I. Ingham HR, Eaton S, Venables CW, Adams PC. Bacteroides fragilis resistant to metronidazole after long-term therapy. Lancet I978; x: 214. 2. Sprott MS, Ingham HR, Hickman JE, Sisson PR. Metronidazole resistant anaerobes. Lancet I983; I: I22o. 3. McWalter PW, Baird DR. Metronidazole resistant anaerobes. Lancet I983; i: I22o. 4. Bushell AC. Bacteriology of superficial and deep tissue infection. In: Hawkey PM, Lewis DA, Eds. Medical bacteriology : a practical approach. Oxford: IRL Press, I989 : 9I-I37. 5. Working Party on Antibiotic Sensitivity Testing of the British Society for Antimicrobial Chemotherapy. A guide to sensitivity testing. J Antimicrob Chemother r991 ; 27 (Suppl D) : 22-29~
6, Hickey MM, Davies UM, Dave J, Vogler M, Wall R. Metronidazole resistant Bacteroides fragilis infection of a prosthetic hipjoint. J Infect I99o; zo: I29-I33. 7, Eme Me A, Acour JF, Goldstein FW. Bacteroides fragilis resistant to metronidazole. J Antimicrob Chemother I983; IZ: 523-524. 10
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8. Tabaqchali S, Pantosti A, Oldfield S. Pyruvate dehydrogenase activity and metronidazole susceptibility in Bacteroidesfragilis. J Antimicrob Chemother I983; Ix: 393-4oo. 9. Dublanchet A, Caillon J, Emond JP, Chandon H, Drugeon HB. Isolation of Bacteroides strains with reduced sensitivity to 5-nitroimidazoles. Eur ff C[in Microbiol I986; 5: 346-347 . Io. Borobio MV, Pascual A, Perea EJ. Increasing resistance of Bacteroidesfragilis group strains to metronidazole in Spain between I977 and I982. Eur ff Clin Microbiol I984; 3 (2): I53-I55. i i. Fox AR, Phillips I. T h e antibiotic sensitivity of the Bacteroidesfragilis group in the United Kingdom. ff Antimicrob Chemother I987; 2o: 477-488. I2. Cornick NA, Cuchural GJ, Snydman D R et al. T h e antimicrobial susceptibility patterns of the Bacteroides fragilis group in the United States, I987. ff Antimicrob Chemother I99o; 25: I O I I - - I O I9.
r 3. Brevil J, Bumat C, Patey O, Dublanchet A. Survey of Bacteroides fragilis susceptibility patterns in France. J Antimicrob Chemother I989; 24: 69-75. I4. Rotimi VO, Duerden BI, Ede V, Mackinnon AE. Metronidazole resistant Bacteroides from untreated patient. Lancet t979; i: 833.
CASE REPORT Metronidazole-resistant
Bacteroidesfragilis
wound infection
M. A. T. O ' D o n o g h u e , J. P o t t e r a n d K. D. A l l e n *
Microbiology Department, Whiston Hospital, Prescot, Merseyside L35 5DR, U.K. Accepted for publication I9 December I99I Summary We report the isolation of metronidazole-resistant Bacteroidesfragilis from a postoperative wound abscess in a 72-year-old woman who had not been treated with metronidazole during the preceding 9 months. The case illustrates the need for caution when identifying anaerobes on the basis of metronidazole sensitivity.
Introduction Metronidazole-resistance in Bacteroidesfragilis was first described in the U . K . in I 9 7 8 . 1 Several reports noted the emergence of metronidazole-resistant anaerobes during long-term metronidazole therapy (e.g. I7 days, 2 27 days, z and 3 yearsX) • However, metronidazole resistance is not often reported. As all aerobic organisms are resistant to metronidazole and anaerobes are usually sensitive, this property is used to facilitate the detection of anaerobes in mixed cultures. 4 A 5 #g metronidazole disc is placed on the main inoculum and, after anaerobic incubation, a zone around the metronidazole disc indicates the presence of anaerobes. Absence of a zone may be interpreted as absence of anaerobes. Metronidazole-resistant anaerobes may therefore pass unrecognised in mixed cultures and consequently their true incidence may be underestimated. We report the case of a patient with a post-operative wound abscess from which was isolated a strain of B.fragilis resistant to metronidazole. T h e patient had not received any recent antimicrobial chemotherapy.
Case report A previously healthy 72-year-old woman presented in June I99O with a weeklong history of jaundice and abdominal pain. An initial diagnosis of acute cholecystitis was made and she improved rapidly on intravenous cefuroxime (75o mg 8 hourly) and metronidazole (5oo mg 8 hourly). Five days later, however, her condition suddenly deteriorated. On examination the patient's temperature was 38"5 °C, her pulse rate was IOO beats/min and regular and the blood pressure was IOO/6O m m H g . H e r abdomen was distended with marked tenderness and guarding in the left iliac fossa. Laboratory testing revealed a haemoglobin of IO'9 g/dl with a W B C count * Author to whom correspondence should be sent. oi63-4453/92/o5o21I +04 $08.00/0
© I992 The British Society for the Study of Infection
212
M.A.T. 0'DONOGHUE
ET AL.
of 28"6 x lO9/1. Serum amylase was 20 IU/1. An abdominal X-ray showed dilated loops of small bowel with air under the diaphragm. At laparotomy, a diagnosis of peritonitis secondary to a perforated diverticulum was made and a transverse colostomy performed. Intravenous cefuroxime and metronidazole were continued for 3 weeks. Before her discharge from hospital at the end of July, a barium enema showed the pelvic colon to be severely diseased. T h e patient was therefore readmitted IO weeks later for an elective sigmoid colectomy. She was allowed h o m e after 4 weeks, her post-operative recovery having been complicated by a chest infection which responded to treatment with oral ampicillin. D u r i n g this admission, her w o u n d discharged small amounts of serous fluid, culture of which yielded Streptococcus milleri, coliforms and Bacteroides sp. the last being sensitive to metronidazole. N o additional antibiotics were prescribed. Five m o n t h s later the patient was admitted a third time. Closure of her colostomy was performed without antibiotic prophylaxis and she was discharged h o m e r r days later after an uneventful recovery. D u r i n g this admission she received no antibiotics. Five days after her discharge, however, she presented to the Accident and Emergency D e p a r t m e n t complaining of a purulent discharge from her colostomy wound. On examination she appeared well and was apyrexial. Abdominal examination revealed a 3 x 2 cm abscess at t h e old colostomy site which was discharging purulent blood-stained material. T h e pus yielded a coliform sensitive to ampicillin, augmentin, ciprofloxacin, co-trimoxazole, cefuroxime, gentamicin and piperacillin and a / ? haemolytic Streptococcus sp. (which failed to group using the Wellcome Streptex kit) sensitive to penicillin, ampicillin, augmentin and erythromycin. F r o m the anaerobic neomycin blood agar plate a third colony type became apparent after 48 h. It failed to grow aerobically and, although colonial morphology was suggestive of a Bacteroides sp, no zone appeared around the 2"5 #g metronidazole disc. Subcultures of this colony onto blood agar plates incubated aerobically and anaerobically confirmed that the organism was an obligate anaerobe. Antibiotic disc susceptibility testing showed that it was resistant to metronidazole, penicillin and erythromycin but sensitive to amoxycillin-clavulanic acid, cefoxitin, clindamycin and chloramphenicol. T h e anaerobic Gram-negative bacillus was subsequently identified using the anaerobic A P I system (Bio-M6rieux, France) as Bacteroides fragilis. T h e M I C of metronidazole was determined by using Columbia agar base supplemented with 5 % fresh horse blood with a range of metronidazole concentrations (from 32 # g / m l to o.o6/zg/ml) as described by the Working Party of the British Society for Antimicrobial Chemotherapy. 5 Bacteroides fragilis N C T C 9343 was used as the control. Plates were incubated anaerobically at 37 °C for 48 h. T h e M I C of metronidazole for the patient's isolate was r6 #g/1. Metronidazole resistance was confirmed by the Public Health Laboratory at L u t o n and Dunstable Hospital using 5 #g and 5o #g metronidazole discs. Amoxycillin-clavulanic acid was c o m m e n c e d after the specimen of pus had been obtained. T h e patient was then discharged. One week later the w o u n d was healing well and a further swab did not yield anaerobes. Amoxycillinclavulanic acid was discontinued after I4 days. T h e patient remains well.
Metronidazole-resistant Bacteroides sp.
2 I3
Discussion
A l t h o u g h metronidazole has been in use since the late I95os metronidazole resistance a m o n g anaerobes, including Bacteroides spp., is still u n c o m m o n . T h e r e have been several i n d e p e n d e n t l y confirmed reports of stable metronidazole resistance in B. fragilis 1' 6.7 and a few u n c o n f i r m e d reports of r e d u c e d metronidazole sensitivity in B . f r a g i l i s strains, s-l° Resistance to metronidazole was not d e m o n s t r a t e d in any of the 651 B. fragilis group isolates tested in the U . K . in I987 although slightly r e d u c e d sensitivity was d e m o n s t r a t e d in five o f these strains (less than 1%).11 A s t u d y in the U . S . A . also f o u n d no evidence of metronidazole resistance in 5o6 strains of B . f r a g i l i s tested in I987 .12 In France, metronidazole M I C s greater than 9 rag/1 were only o b s e r v e d in two o f 3o0 strains of B . f r a g i l i s 1~ tested b e t w e e n I987 and I988, M a n y o f the patients from w h o m metronidazole-resistant Bacteroides sp. have been r e p o r t e d had been receiving metronidazole for comparatively long periods of time. 1-3 O u r patient had had metronidazole for 26 days during her initial stay in hospital b u t had not received any in the 9 m o n t h s before the isolation o f this metronidazole-resistant organism. In the intervening period Bacteroides sp. apparently sensitive to metronidazole, had been isolated from w o u n d swabs on at least one occasion. U n f o r t u n a t e l y , this strain is no longer available in the laboratory and it is impossible to establish w h e t h e r the metronidazole-sensifive and resistant Bacteroides spp. were of the same strain in which resistance determinants had developed. It is recognised, however, that metronidazole-resistant strains of Bacteroides sp. can be isolated from patients w h o have never received metronidazole. 1~ T h i s case demonstrates the need for caution w h e n using metronidazole discs to flag up anaerobes. A l t h o u g h metronidazole resistance is rare it does occur and appears to be b e c o m i n g m o r e c o m m o n in certain E u r o p e a n countries, e.g. Spain. 1° It is important therefore not to exclude the presence of an obligate anaerobe p u r e l y on the basis o f resistance to a metronidazole disc. Awareness o f the existence of such isolates will help to establish the true incidence of metronidazole-resistant anaerobes. (The authors wish to thank Mrs Susan Morgan for secretarial assistance in the preparation of this paper.) References I. Ingham HR, Eaton S, Venables CW, Adams PC. Bacteroides fragilis resistant to metronidazole after long-term therapy. Lancet I978; x: 214. 2. Sprott MS, Ingham HR, Hickman JE, Sisson PR. Metronidazole resistant anaerobes. Lancet I983; I: I22o. 3. McWalter PW, Baird DR. Metronidazole resistant anaerobes. Lancet I983; i: I22o. 4. Bushell AC. Bacteriology of superficial and deep tissue infection. In: Hawkey PM, Lewis DA, Eds. Medical bacteriology : a practical approach. Oxford: IRL Press, I989 : 9I-I37. 5. Working Party on Antibiotic Sensitivity Testing of the British Society for Antimicrobial Chemotherapy. A guide to sensitivity testing. J Antimicrob Chemother r991 ; 27 (Suppl D) : 22-29~
6, Hickey MM, Davies UM, Dave J, Vogler M, Wall R. Metronidazole resistant Bacteroides fragilis infection of a prosthetic hipjoint. J Infect I99o; zo: I29-I33. 7, Eme Me A, Acour JF, Goldstein FW. Bacteroides fragilis resistant to metronidazole. J Antimicrob Chemother I983; IZ: 523-524. 10
J I N 25
M. A. T. O ' D O N O G H U E E T AL.
214
8. Tabaqchali S, Pantosti A, Oldfield S. Pyruvate dehydrogenase activity and metronidazole susceptibility in Bacteroidesfragilis. J Antimicrob Chemother I983; Ix: 393-4oo. 9. Dublanchet A, Caillon J, Emond JP, Chandon H, Drugeon HB. Isolation of Bacteroides strains with reduced sensitivity to 5-nitroimidazoles. Eur ff C[in Microbiol I986; 5: 346-347 . Io. Borobio MV, Pascual A, Perea EJ. Increasing resistance of Bacteroidesfragilis group strains to metronidazole in Spain between I977 and I982. Eur ff Clin Microbiol I984; 3 (2): I53-I55. i i. Fox AR, Phillips I. T h e antibiotic sensitivity of the Bacteroidesfragilis group in the United Kingdom. ff Antimicrob Chemother I987; 2o: 477-488. I2. Cornick NA, Cuchural GJ, Snydman D R et al. T h e antimicrobial susceptibility patterns of the Bacteroides fragilis group in the United States, I987. ff Antimicrob Chemother I99o; 25: I O I I - - I O I9.
r 3. Brevil J, Bumat C, Patey O, Dublanchet A. Survey of Bacteroides fragilis susceptibility patterns in France. J Antimicrob Chemother I989; 24: 69-75. I4. Rotimi VO, Duerden BI, Ede V, Mackinnon AE. Metronidazole resistant Bacteroides from untreated patient. Lancet t979; i: 833.
