Journal
of Hospital
Infection
Mkrococcus
(1990) 16, 67-73
and Stomatococcus infections
J. T. Magee*,
I. A. Burnett,
spp. from
J. M. Hindmarch
Department of Bacteriology, Royal “Department of Microbiology,
human
and R. C. Spencer
Hallamshire Hospital, Shefield Children’s Hospital, Shefield
Accepted for publication
7 March
and
1990
Summary: Infections with Micrococcus cus mucilaginosus in one patient are
spp. in six patients and Stomatococdescribed. Two of the Micrococcus infections occurred in leukaemic patients with indwelling lines, six episodes occurred in three patients undergoing continuous ambulatory peritoneal dialysis and one occurred in a patient with a ventriculo-peritoneal shunt. Stomatococcus was isolated from fluid draining from a sub-dural haematoma. Colony morphology, oxidase reaction and resistance to nitrofurantoin were useful in differentiation of micrococci from staphylococci. Incidence and risk factors for micrococcal infections appear similar to those for infections with coagulase-negative staphylococci (CNS), but the literature is confused due to changes in the definitions of these genera.
Keywords: CAPD;
Micrococcus;
shunt;
indwelling
Stomatococcus; line
coagulase-negative
staphylococci;
infections.
Introduction
The Micrococcaceae comprises several genera (Schleifer, 1984), of which Staphylococcus is the most important in human disease. Of the remaining genera, Micrococcus spp. have been implicated as pathogens in a few reports (Albertson et al., 1978; Marples & Richardson, 1980; Marsik & Brake, 1982; Richardson et al., 1984; Ambler et al., 1986; Wharton et al., 1986; Shapiro et al., 1988; Spencer, 1988) as have Stomatococcus spp. (Rubin et al., 1978; Prag et al., 1985; Coudron et al., 1987; Chomarat & Rochette, 1988), but are usually regarded as non-pathogens. Prior to 1984, Micrococcus spp. had not been isolated in an unequivocally pathogenic role at the Royal Hallamshire Hospital, but between 1984 and 1989, significant isolates were increasingly common and, in 1989, a strain of Stomatococcus mucilaginosus was isolated in a possibly pathogenic role. The following case reports document the infections in which these organisms were most clearly implicated. Correspondence 019556701/90/050067+07
to: J. T. Magee. $03.00/O
0 1990 The Hospital
67
Infection
Society
J. T. Magee
68
Materials
et al.
and methods
Blood cultures, continuous ambulatory peritoneal dialysis (CAPD) fluid and cerebrospinal fluid (CSF) were cultured by conventional methods as previously described (Spencer & Fenton, 1984; Cross et al., 1986). Colonies were examined for pigmentation and morphology. Gram-stained films were examined, and oxidase (Cowan, 1974a) and catalase (Cowan, 1974b) tests performed. The APIStaph system (API-Bio Merieux, Basingstoke) was used in biochemical identification (Brun et al., 1978), and susceptibility to nitrofurans (Curry & Borovian, 1976) was assessed with 200 gg nitrofurantoin discs. Other antibiotic susceptibilities were assessed by the breakpoint method (Pease et al., 1988). Strains were subsequently tested in batches for lysostaphin (Schleifer & Kloos, 1975a) and lysozyme (Poutrel & Kaffin, 1981) susceptibility, and acid production on glycerol-erythromycin agar (Schleifer & Kloos, 1975b), as the reagents and media required for these tests were too labile or expensive for routine use. Case reports Details
of the cases are summarized in Table I. pyrexial after cytotoxic therapy. Blood from a Hickman line yielded a ~icrococcus sp. The pyrexia resolved after 5 days vancomycin treatment, only to recur 2 weeks later, when a &$z&~occus sp. with the same susceptibility and colonial appearance was isolated from line blood. Vancomycin treatment was resumed for 5 days and the Hickman line was removed. The infection did not recur. Case 2 became pyrexial after cytotoxic therapy. Blood from a Hickman line yielded a ~z&~occus sp. from all cultures after 24 h and concurrently sampled peripheral blood yielded this organism from one bottle after 3 days.
Case 1 became
Table
I.
Details of the cases of Micrococcus and Stomatococcusinfection Age
Case
i 3 4 5 ;
Sex F M M F F
(yrs) 20 :: 77 42 32 87
Underlying disease? AML AML RF RF RF MA SDH
InfectionS IHL IHL CAPDP CAPDP CAPDP Shunt ISDH
Species isolated* Mic.
sp.
Mic. sp. Mic. sp. Mic. sp. Mic. sp. Mic. sp. Stom. mu.
Number episodes
of
1 1 3 1 :
1
t AML, acute my&id leukaemia; RF, renal failure; MA microcystic astrocytoma of the mid brain; SDH, sub-dural haematoma. $ IHL, infected Hickman line; CAPDP, CAPD peritonitis; Shunt, infected ventriculo-peritoneal shunt; ISDH, infected sub-dural haematoma. * Mic. sp., Micrococcus sp.; Stem. mu., Stomatococcus mucilaginosus; all strains described were isolated in pure culture.
Micrococcus
spp.
in
infection
69
Empirical treatment with piperacillin and gentamicin was successful. The Hickman line was not removed. Case 3 suffered recurrent episodes of CAPD peritonitis. In three episodes, Micrococcus sp. was isolated from a dialysis fluid. White cell counts (WCC) of the CAPD fluid were 550 and 800 mmm3 respectively on the second and third isolations. Gram-positive cocci were seen in the centrifugate of the third sample. Treatment with intraperitoneal (ip) vancomycin was successful in each of these episodes. The patient suffered several further episodes of CAPD peritonitis in which various organisms, including Pseudomonas aeruginosa, were implicated. Case 4 was admitted with CAPD peritonitis and a Micrococcus sp. was isolated from the CAPD fluid (WCC 270 mmm3). After vancomycin treatment the infection resolved, but recurred 4 weeks later, when a Micrococcus sp. with similar colonial morphology was isolated from a dialysis fluid (WCC 475 mme3). This isolate was resistant to erythromycin. The infection resolved when treated with ip cefuroxime. Case 5 was admitted with a seventh episode of CAPD peritonitis. A Micrococcus sp. was isolated from two dialysis fluids (WCC 840; 260 mmp3; no organisms seen on microscopy). Treatment with ip cefuroxime was not successful, but the infection resolved after removal of the Tenkhoff catheter. Case 6 suffered a low grade microcystic astrocytoma of the mid-brain. A ventriculo-peritoneal shunt inserted to relieve intracranial pressure became blocked on several occasions necessitating readmission. The patient was admitted later with symptoms of a shunt infection. A Micrococcus sp. was isolated from two samples of cerebrospinal fluid aspirated from the shunt system (WCC 460, 75% polymorphs; WCC c. 1000mm-3, mostly degenerate polymorphs containing Gram-positive cocci in tetrads). Treatment with flucloxacillin and chloramphenicol was unsuccessful, presumably due to colonization of the shunt tubing and reservoir. The system was removed and an external ventricular drain inserted. The patient continued to deteriorate, antibiotics were withdrawn, and the patient died. Case 7 underwent evacuation of a left sub-dural haematoma, followed by insertion of a Jackson-Pratt drain. The patient was in a confused state and repeatedly handled the drain, eventually pulling it out. A new drain was inserted because of recurrence of the sub-dural collection. Symptoms of meningitis were not present, but fluid taken on insertion of the second drain contained Gram-positive cocci and many pus cells, and yielded a pure culture of Stomatococcus mucilaginosus. The patient was treated with chloramphenicol, flucloxacillin and metronidazole and remained stable until transfer to another hospital.
Laboratory jindings Micrococcus spp. yielded visible colonies after 24 h incubation.
The colonies were domed and usually bright yellow. This appearance, most characteristic
70
J. T. Magee
et al.
after 48 h incubation, was distinct from the flat or slightly raised white, buff or grey colonies characteristic of coagulase-negative staphylococci (CNS). Gram films showed large Gram-positive cocci in tetrads, pairs and occasional cubical packets. All strains were catalase-positive and most were oxidase-positive in primary culture. When positive, oxidase provided a rapid presumptive differential test for Micrococcus spp. In APIStaph, production of acid was negative, or weak and limited to a few sugars after 48 h incubation; typical profiles were 0000006 and 0000004 (M~crococcus spp., excellent identification). Colonies grew to the edge of a 200 l.tg nitrofurantoin disc. By contrast CNS were susceptible to nitrofurantoin. This test was a reliable, inexpensive and simple method for discriminating between CNS and micrococci. Strains were susceptible to penicillin, methicillin, tetracycline, vancomycin, gentamicin, and, with one exception (Case 4), erythromycin. The isolate of Stomatococcus mucilaginosus gave small, domed, adherent grey-brown colonies after 24 h incubation. The colony material was tough, and strings were produced when a loop was touched to the colony and withdrawn. Gram films showed large Gram-positive cocci arranged in tetrads, pairs and cubical aggregates. Capsule material extending to more than twice the cell diameter was seen in capsule stains. Oxidase and catalase tests were negative. The APIStaph profile was 6412114, indicating M. varians, M. kristinae, Staph. hominis or Stom. mucilaginosus as possible identifications. The latter was confirmed by the negative catalase reaction, typical capsule and colony appearance. The strain was susceptible to vancomycin, tetracycline and penicillin, methicillin, erythromycin, nitrofurantoin. Discussion
The skin commensals CNS (Pfaller & Herwaldt, 1988) and Corynebacterium (Finger et al., 1983; Soriano et al., 1988), were previously regarded but have recently become important in hospital as non-pathogenic, infections associated with indwelling intravenous lines, cardiac valve prostheses, ventricular shunts, or CAPD peritonitis. Other infections by these organisms are rare, indicating their poor pathogenic potential. In the cases described here and elsewhere, isolation of Micrococcus spp., a skin commensal and Stomatococcus mucilaginosus, a mouth commensal, follow a similar pattern. Features of these infections are: they occur at sites which are remote from the host defence systems; plastic surfaces are involved, where materials deposited from host fluids may protect the initial inoculum from host defences; intermittent flushing with extraneous fluids deplete the host defences at the site, and repeated or complex handling procedures provide opportunities for entry of organisms. The importance of these factors may
jeikeium
Micrococcus
spp.
in infection
71
differ between the types of infection, but they clearly provide opportunities for relatively non-pathogenic commensal organisms to reach systemic sites where they may proliferate. The literature on micrococcal infections is difficult to interpret because the definitions of lMicrococcus and Staphylococcus have changed repeatedly, and crucial identification tests in the current classification were described only recently. However, strains clearly identified as Micrococcus spp. have been reported in infection. Richardson et al. (1984) surveyed 137 cases of endocarditis caused by coagulase-negative Micrococcaceae (CNM), and found five Micrococcus spp., four from patients with prosthetic valves. Gahrn-Hansen et al. (1987) found 12% micrococci in a series of 138 CNM from blood cultures, but did not indicate their significance. Marsik & Brake (1982) found 18 strains among 299 CNM, 2/86 from blood cultures, 7/47 from wounds, 4/68 from urines and 5/68 from other sources; they considered five wound and three urinary isolates to be non-significant. As with CNS, micrococci are common contaminants in clinical specimens, and assessment of significance may be difficult. Spencer (1988) reported 18 isolates in a survey of 750 cases of CAPD peritonitis, Herbert et al. (1988) found 18 micrococci and two stomatococci in a series of 1240 clinical isolates of CNM, and Shapiro et al. (1988) recorded one micrococcus in a survey of 20 ventricular shunt infections. However, clinical findings for the non-staphylococcal isolates were not included in these surveys. There are more detailed reports of micrococci in endocarditis (Marples & Richardson, 1980), septic shock (Albertson et al., 1978), septicaemia with secondary central nervous system infection (Ambler et al., 1986) and septic arthritis of the hip (Wharton et al., 1986). Reports of S. mucilaginosus have been mainly of endocarditis in patients with damaged or artificial heart valves (Rubin et al., 1978; Prag et al., 1985; Coudron et al., 1987), although other infections have been reported (Chromarat & Rochette, 1988; Lemozy et al., 1990). Only one ItIicrococcus strain in this series showed resistance (to erythromycin), although penicillin, methicillin, erythromycin and tetracycline resistance, and strains resistant to isoxazolyl penicillins but not penicillin have been reported (Albertson et al., 1978; Marples & Richardson, 1980; Marsik & Brake, 1982; Wharton et aZ., 1986). Strains of Stomatococcus may be resistant to gentamicin, penicillin and erythromycin (Chomarat & Rochete, 1988). Micrococci are more susceptible to skin disinfection than CNS (Kaplowitz et al., 1988), a possible factor in their low relative incidence. These reports show that Micrococcus sp. and Stomatococcus mucilaginosus isolates from blood cultures, indwelling lines, shunts, valves and CAPD fluids cannot be lightly dismissed as non-pathogens. Despite a superficial resemblance to CNS, they are clearly distinct in DNA and cell wall composition (Schleifer, 1984). More information on the incidence and pathology of these infections is required.
72
J. T. Magee
et al.
References Albertson,
D.,
Natsios,
G. A. & Glickman,
Archives of Internal Ambler, M. infection
Medicine
w., Homans, in a young
Medicine
R. (1978).
Septic
shock
with
Micrococcus
luteus.
138. 487-488.
A. C. & O’Shea, immunocompromised
P. A. (1986). An unusual central host. Archives of Pathology
nervous
system
and Laboratory
110, 497-501.
Brun,
Y., Fleurette, J. & Forey, F. (1978). Micromethod coagulase negative staphylococci. Journal of Clinical Chomarat, M. & Rochette, A. (1988). Signification
mucilaginosus.
La Presse Medicale
for
biochemical
Microbiology de
l’isolement
identification
of
5, 503-508. de Stomatococcus
17, 537-538.
Coudron, P. E., Markowitz, S. M., Mohanty, L. B., Schatzki, P. F. & Payne, J. M. (1987). Isolation of Stomatococcus mucilaginosus from drug user with endocarditis. Journal of Clinical Microbiology 25, 1359-I 363. Cowan, S. T. (1974a). In Cowan and Steel’s Manualfor the Identification of Medical Bacteria, p. 171 (Method 1). Cambridge University Press, Cambridge. Cowan, S. T. (1974b). In Cowan and Steel’s Manualfor the Identification of Medical Bacteria, p. 177 (Method 1). Cambridge University Press, Cambridge. Cross, A. J., Haworth, E. & Spencer, R. C. (1986). A re-evaluation of the pour plate blood culture method for the detection of candida and other septicaemias. Journal of Hospital
Infection
7, 74-77.
Curry,
J. C. & Borovian, G. E. (1976). Selective medium for distinguishing micrococci from staphylococci in the clinical laboratory. Journal of Clinical Microbiology 4, 455457. Finger, H., Wirsing von Koenig, C. H., Wichmann, S., Becker-Boost, E. & Drechsler, H. J. (1983). Clinical significance of resistant corynebacteria Group JK. Lancet 1, 538. Gahrn-Hansen, B., Heltberg, O., Rosdahl, V. T. & Sogaard, P. (1987). Evaluation of a conventional routine method for identification of clinical isolates of coagulase-negative Acta Pathologica et Microbiologica Staphylococcus and Micrococcus species. Immunologica Scandinavia. Section B 95, 283-292. Herbert, G. A., Crowder, C. G., Hancock, G. A., Jarvis, W. R. & Thornsberry, C. (1988). Characteristics of coagulase-negative staphylococci that help differentiate these species and other members of the family Micrococcaceae. Journal of Clinical Microbiology 26, 1039-1049. Kaplowitz, L. G., Comstock, J. A., Landwehr, D. M., Dalton, H. P. & Mathall, C. G. (1988). Prospective study of microbial colonization of the nose and skin and infection of the vascular access site in haemodialysis patients. Journal of Clinical Microbiology 26, 1257-1262. Lemozy, J., Maestre, P., Huguet, F., Chomarat, M., Dabernat, H. & Lareng, M. B. (1990). Source of infection in Stomatococcus mucilaginosus septicaemia. Lancet 335, 416. Marples, R. R. & Richardson, J. F. (1980). Micrococcus in the blood. Journal of Medical
Microbiology Marsik,
13, 355-362.
F. J. & Brake, coagulase-negative
Microbiology Pease,
S. (1982). Species identification staphylococci isolated from
to 17 antibiotics of of Clinical
Journal
15, 640-645.
A. A., Wheat, P. F. & Harris, biochemical identification using
Laboratory
and susceptibility clinical specimens.
D. M. (1988). Antimicrobial multipoint inoculation:
susceptibility 5 years experience.
testing
and
Medical
Sciences 15, 28-33.
Pfaller,
M. A. & Herwaldt, L. A. (1988). Laboratory, clinical, and epidemiological aspects of coagulase-negative staphylococci. Clinical Microbiology Reviews 1, 281-299. Poutrel, B. & Kaffin, J.-P. (1981). Lysostaphin disk test for routine presumptive identification of staphylococci. Journal of Clinical Microbiology 13, 1023-1025. Prag, J., Kjoller, E. & Espersen, F. (1985). Stomatococcus mucilaginosus endocarditis. European Journal of Clinical Microbiology 4, 422-424. Richardson, J. F., Marples, R. R. & de Saxe, M. J. (1984). Characters of coagulase-negative staphylococci and micrococci from cases of endocarditis. Journal of Hospital Infection 5, 164-171. Rubin, S. J., Lyons, R. W. & Murcia, A. J. (1978). Endocarditis associated with cardiac catheterisation due to Gram-positive coccus designated Micrococcus mucilaginosus
incertae sedis. Journal
of Clinical
Microbiology
7, 546-549.
Schleifer, K. H. & Kloos, W. E. (1975a). Isolation and characterisation human skin. I. Innternational Journal of Systematic Bacteriology
of staphylococci
25, 50-61.
from
Micrococcus
spp. in infection
73
Schleifer, K. H. & Kloos, W. E. (1975b). A simple test system for the separation of staphylococci from micrococci. Journal of Clinical Microbiology 1, 337-338. Schleifer, K. H. (1984). Micrococcaceae. In Bergey’s Manual of Systematic Bacteriology, (Holt, J. G. et al., Eds), pp. 1003-1043. Williams and Wilkins, Baltimore. Shapiro, S., Boaz, J., Kleiman, M., Kalsbeck, J. & Mealey, J. (1988). Origin of organisms infecting ventricular shunts. Neurosurgery 22, 868-872. Soriano, F., Rodriguez-Tudela, J. L., Fernandez-Roblas, R., Aguado, J. M. & Santamaria, M. (1988). Skin colonisation by Corynebacterium groups D2 and JK in hospitalised patients. Journal of Clinical Microbiology 26, 1878-1880. Spencer, R. C. (1988). Infections in continuous ambulatory peritoneal dialysis. Journal of Clinical Microbiology 27, l-9. Spencer, R. C. & Fenton, P. A. (1984). Infective complications of peritoneal dialysis.Journal of Hospital Infection 5, 233-240. Wharton, M., Rice, J. R., McCallum, R. & Gallis, H. A. (1986). Septic arthritis due to Micrococcus luteus. Journal of Rheumatology 13, 659-660.
of Hospital
Infection
Mkrococcus
(1990) 16, 67-73
and Stomatococcus infections
J. T. Magee*,
I. A. Burnett,
spp. from
J. M. Hindmarch
Department of Bacteriology, Royal “Department of Microbiology,
human
and R. C. Spencer
Hallamshire Hospital, Shefield Children’s Hospital, Shefield
Accepted for publication
7 March
and
1990
Summary: Infections with Micrococcus cus mucilaginosus in one patient are
spp. in six patients and Stomatococdescribed. Two of the Micrococcus infections occurred in leukaemic patients with indwelling lines, six episodes occurred in three patients undergoing continuous ambulatory peritoneal dialysis and one occurred in a patient with a ventriculo-peritoneal shunt. Stomatococcus was isolated from fluid draining from a sub-dural haematoma. Colony morphology, oxidase reaction and resistance to nitrofurantoin were useful in differentiation of micrococci from staphylococci. Incidence and risk factors for micrococcal infections appear similar to those for infections with coagulase-negative staphylococci (CNS), but the literature is confused due to changes in the definitions of these genera.
Keywords: CAPD;
Micrococcus;
shunt;
indwelling
Stomatococcus; line
coagulase-negative
staphylococci;
infections.
Introduction
The Micrococcaceae comprises several genera (Schleifer, 1984), of which Staphylococcus is the most important in human disease. Of the remaining genera, Micrococcus spp. have been implicated as pathogens in a few reports (Albertson et al., 1978; Marples & Richardson, 1980; Marsik & Brake, 1982; Richardson et al., 1984; Ambler et al., 1986; Wharton et al., 1986; Shapiro et al., 1988; Spencer, 1988) as have Stomatococcus spp. (Rubin et al., 1978; Prag et al., 1985; Coudron et al., 1987; Chomarat & Rochette, 1988), but are usually regarded as non-pathogens. Prior to 1984, Micrococcus spp. had not been isolated in an unequivocally pathogenic role at the Royal Hallamshire Hospital, but between 1984 and 1989, significant isolates were increasingly common and, in 1989, a strain of Stomatococcus mucilaginosus was isolated in a possibly pathogenic role. The following case reports document the infections in which these organisms were most clearly implicated. Correspondence 019556701/90/050067+07
to: J. T. Magee. $03.00/O
0 1990 The Hospital
67
Infection
Society
J. T. Magee
68
Materials
et al.
and methods
Blood cultures, continuous ambulatory peritoneal dialysis (CAPD) fluid and cerebrospinal fluid (CSF) were cultured by conventional methods as previously described (Spencer & Fenton, 1984; Cross et al., 1986). Colonies were examined for pigmentation and morphology. Gram-stained films were examined, and oxidase (Cowan, 1974a) and catalase (Cowan, 1974b) tests performed. The APIStaph system (API-Bio Merieux, Basingstoke) was used in biochemical identification (Brun et al., 1978), and susceptibility to nitrofurans (Curry & Borovian, 1976) was assessed with 200 gg nitrofurantoin discs. Other antibiotic susceptibilities were assessed by the breakpoint method (Pease et al., 1988). Strains were subsequently tested in batches for lysostaphin (Schleifer & Kloos, 1975a) and lysozyme (Poutrel & Kaffin, 1981) susceptibility, and acid production on glycerol-erythromycin agar (Schleifer & Kloos, 1975b), as the reagents and media required for these tests were too labile or expensive for routine use. Case reports Details
of the cases are summarized in Table I. pyrexial after cytotoxic therapy. Blood from a Hickman line yielded a ~icrococcus sp. The pyrexia resolved after 5 days vancomycin treatment, only to recur 2 weeks later, when a &$z&~occus sp. with the same susceptibility and colonial appearance was isolated from line blood. Vancomycin treatment was resumed for 5 days and the Hickman line was removed. The infection did not recur. Case 2 became pyrexial after cytotoxic therapy. Blood from a Hickman line yielded a ~z&~occus sp. from all cultures after 24 h and concurrently sampled peripheral blood yielded this organism from one bottle after 3 days.
Case 1 became
Table
I.
Details of the cases of Micrococcus and Stomatococcusinfection Age
Case
i 3 4 5 ;
Sex F M M F F
(yrs) 20 :: 77 42 32 87
Underlying disease? AML AML RF RF RF MA SDH
InfectionS IHL IHL CAPDP CAPDP CAPDP Shunt ISDH
Species isolated* Mic.
sp.
Mic. sp. Mic. sp. Mic. sp. Mic. sp. Mic. sp. Stom. mu.
Number episodes
of
1 1 3 1 :
1
t AML, acute my&id leukaemia; RF, renal failure; MA microcystic astrocytoma of the mid brain; SDH, sub-dural haematoma. $ IHL, infected Hickman line; CAPDP, CAPD peritonitis; Shunt, infected ventriculo-peritoneal shunt; ISDH, infected sub-dural haematoma. * Mic. sp., Micrococcus sp.; Stem. mu., Stomatococcus mucilaginosus; all strains described were isolated in pure culture.
Micrococcus
spp.
in
infection
69
Empirical treatment with piperacillin and gentamicin was successful. The Hickman line was not removed. Case 3 suffered recurrent episodes of CAPD peritonitis. In three episodes, Micrococcus sp. was isolated from a dialysis fluid. White cell counts (WCC) of the CAPD fluid were 550 and 800 mmm3 respectively on the second and third isolations. Gram-positive cocci were seen in the centrifugate of the third sample. Treatment with intraperitoneal (ip) vancomycin was successful in each of these episodes. The patient suffered several further episodes of CAPD peritonitis in which various organisms, including Pseudomonas aeruginosa, were implicated. Case 4 was admitted with CAPD peritonitis and a Micrococcus sp. was isolated from the CAPD fluid (WCC 270 mmm3). After vancomycin treatment the infection resolved, but recurred 4 weeks later, when a Micrococcus sp. with similar colonial morphology was isolated from a dialysis fluid (WCC 475 mme3). This isolate was resistant to erythromycin. The infection resolved when treated with ip cefuroxime. Case 5 was admitted with a seventh episode of CAPD peritonitis. A Micrococcus sp. was isolated from two dialysis fluids (WCC 840; 260 mmp3; no organisms seen on microscopy). Treatment with ip cefuroxime was not successful, but the infection resolved after removal of the Tenkhoff catheter. Case 6 suffered a low grade microcystic astrocytoma of the mid-brain. A ventriculo-peritoneal shunt inserted to relieve intracranial pressure became blocked on several occasions necessitating readmission. The patient was admitted later with symptoms of a shunt infection. A Micrococcus sp. was isolated from two samples of cerebrospinal fluid aspirated from the shunt system (WCC 460, 75% polymorphs; WCC c. 1000mm-3, mostly degenerate polymorphs containing Gram-positive cocci in tetrads). Treatment with flucloxacillin and chloramphenicol was unsuccessful, presumably due to colonization of the shunt tubing and reservoir. The system was removed and an external ventricular drain inserted. The patient continued to deteriorate, antibiotics were withdrawn, and the patient died. Case 7 underwent evacuation of a left sub-dural haematoma, followed by insertion of a Jackson-Pratt drain. The patient was in a confused state and repeatedly handled the drain, eventually pulling it out. A new drain was inserted because of recurrence of the sub-dural collection. Symptoms of meningitis were not present, but fluid taken on insertion of the second drain contained Gram-positive cocci and many pus cells, and yielded a pure culture of Stomatococcus mucilaginosus. The patient was treated with chloramphenicol, flucloxacillin and metronidazole and remained stable until transfer to another hospital.
Laboratory jindings Micrococcus spp. yielded visible colonies after 24 h incubation.
The colonies were domed and usually bright yellow. This appearance, most characteristic
70
J. T. Magee
et al.
after 48 h incubation, was distinct from the flat or slightly raised white, buff or grey colonies characteristic of coagulase-negative staphylococci (CNS). Gram films showed large Gram-positive cocci in tetrads, pairs and occasional cubical packets. All strains were catalase-positive and most were oxidase-positive in primary culture. When positive, oxidase provided a rapid presumptive differential test for Micrococcus spp. In APIStaph, production of acid was negative, or weak and limited to a few sugars after 48 h incubation; typical profiles were 0000006 and 0000004 (M~crococcus spp., excellent identification). Colonies grew to the edge of a 200 l.tg nitrofurantoin disc. By contrast CNS were susceptible to nitrofurantoin. This test was a reliable, inexpensive and simple method for discriminating between CNS and micrococci. Strains were susceptible to penicillin, methicillin, tetracycline, vancomycin, gentamicin, and, with one exception (Case 4), erythromycin. The isolate of Stomatococcus mucilaginosus gave small, domed, adherent grey-brown colonies after 24 h incubation. The colony material was tough, and strings were produced when a loop was touched to the colony and withdrawn. Gram films showed large Gram-positive cocci arranged in tetrads, pairs and cubical aggregates. Capsule material extending to more than twice the cell diameter was seen in capsule stains. Oxidase and catalase tests were negative. The APIStaph profile was 6412114, indicating M. varians, M. kristinae, Staph. hominis or Stom. mucilaginosus as possible identifications. The latter was confirmed by the negative catalase reaction, typical capsule and colony appearance. The strain was susceptible to vancomycin, tetracycline and penicillin, methicillin, erythromycin, nitrofurantoin. Discussion
The skin commensals CNS (Pfaller & Herwaldt, 1988) and Corynebacterium (Finger et al., 1983; Soriano et al., 1988), were previously regarded but have recently become important in hospital as non-pathogenic, infections associated with indwelling intravenous lines, cardiac valve prostheses, ventricular shunts, or CAPD peritonitis. Other infections by these organisms are rare, indicating their poor pathogenic potential. In the cases described here and elsewhere, isolation of Micrococcus spp., a skin commensal and Stomatococcus mucilaginosus, a mouth commensal, follow a similar pattern. Features of these infections are: they occur at sites which are remote from the host defence systems; plastic surfaces are involved, where materials deposited from host fluids may protect the initial inoculum from host defences; intermittent flushing with extraneous fluids deplete the host defences at the site, and repeated or complex handling procedures provide opportunities for entry of organisms. The importance of these factors may
jeikeium
Micrococcus
spp.
in infection
71
differ between the types of infection, but they clearly provide opportunities for relatively non-pathogenic commensal organisms to reach systemic sites where they may proliferate. The literature on micrococcal infections is difficult to interpret because the definitions of lMicrococcus and Staphylococcus have changed repeatedly, and crucial identification tests in the current classification were described only recently. However, strains clearly identified as Micrococcus spp. have been reported in infection. Richardson et al. (1984) surveyed 137 cases of endocarditis caused by coagulase-negative Micrococcaceae (CNM), and found five Micrococcus spp., four from patients with prosthetic valves. Gahrn-Hansen et al. (1987) found 12% micrococci in a series of 138 CNM from blood cultures, but did not indicate their significance. Marsik & Brake (1982) found 18 strains among 299 CNM, 2/86 from blood cultures, 7/47 from wounds, 4/68 from urines and 5/68 from other sources; they considered five wound and three urinary isolates to be non-significant. As with CNS, micrococci are common contaminants in clinical specimens, and assessment of significance may be difficult. Spencer (1988) reported 18 isolates in a survey of 750 cases of CAPD peritonitis, Herbert et al. (1988) found 18 micrococci and two stomatococci in a series of 1240 clinical isolates of CNM, and Shapiro et al. (1988) recorded one micrococcus in a survey of 20 ventricular shunt infections. However, clinical findings for the non-staphylococcal isolates were not included in these surveys. There are more detailed reports of micrococci in endocarditis (Marples & Richardson, 1980), septic shock (Albertson et al., 1978), septicaemia with secondary central nervous system infection (Ambler et al., 1986) and septic arthritis of the hip (Wharton et al., 1986). Reports of S. mucilaginosus have been mainly of endocarditis in patients with damaged or artificial heart valves (Rubin et al., 1978; Prag et al., 1985; Coudron et al., 1987), although other infections have been reported (Chromarat & Rochette, 1988; Lemozy et al., 1990). Only one ItIicrococcus strain in this series showed resistance (to erythromycin), although penicillin, methicillin, erythromycin and tetracycline resistance, and strains resistant to isoxazolyl penicillins but not penicillin have been reported (Albertson et al., 1978; Marples & Richardson, 1980; Marsik & Brake, 1982; Wharton et aZ., 1986). Strains of Stomatococcus may be resistant to gentamicin, penicillin and erythromycin (Chomarat & Rochete, 1988). Micrococci are more susceptible to skin disinfection than CNS (Kaplowitz et al., 1988), a possible factor in their low relative incidence. These reports show that Micrococcus sp. and Stomatococcus mucilaginosus isolates from blood cultures, indwelling lines, shunts, valves and CAPD fluids cannot be lightly dismissed as non-pathogens. Despite a superficial resemblance to CNS, they are clearly distinct in DNA and cell wall composition (Schleifer, 1984). More information on the incidence and pathology of these infections is required.
72
J. T. Magee
et al.
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