Species identification, antibiotic sensitivity and slime production of coagulase-negative staphylococci isolated from clinical specimens

Virulence and toxigenicity of coagulase-negative staphylococci in Nigerian traditional fermented foods

The incidence of coagulase-negative staphylococci (CoNS) may render food unsafe, as the clinical isolates have been reported to exude virulent traits. A total of 255 CoNS isolates from 6 traditional fermented foods (nono, kunu, wara, iru, ogi, and kindirmo) from North Central Nigeria, identified as Staphylococcus epidermidis, Staphylococcus simulans, Staphylococcus xylosus, Staphylococcus kloosii, and Staphylococcus caprae, were investigated for virulence traits. The strains were examined for biofilm formation and production of hyaluronidase, DNase, TNase, haemolysins, and superantigenic toxins (SEA, SEB, SEC, SED, and TSST-1) using standard and genotypic methods. The analysis of virulence factors revealed the production of slime in 200 isolates (78.4%); α-haemolysin in 136 (53.3%); β-haemolysin in 43 (16.9%); DNase in 199 (78.0%); TNase in 29 (11.4%); hyaluronidase in 125 (49.0%); TSST-1 in 119 (46.7%); and enterotoxin-producing isolates SEA, SEB, SEC, and SED in 61 (23.9%), 19 (7.5%), 9 (3.5%), and 8 (3.1%), respectively. PCR analysis detected tsst-1, sea, seb, and sec genes. The ability of these microorganisms to exhibit virulence evokes the potential to cause disease especially under determinate conditions or in immune-compromised patients. The occurrence of CoNS in food should not be ignored nor their pathogenic potential considered as insignificant, rather safety measures should be taken to reduce or totally eliminate their occurrence in foods.

Epidemiological and molecular characterization ofStaphylococcus haemolyticusstrains, from a hematology ward, with decreased susceptibility to glycopeptides

In the present study, we report on the reduced susceptibility to teicoplanin among clinical isolates of Staphylococcus haemolyticus in a hematology ward of a teaching hospital. The molecular characterization of 17 S. haemolyticus strains was performed using mec gene complex classification, pulsed-field gel electrophoresis analysis, and minimum inhibitory concentration examination. Pulsotype A strains carrying a class C2 mec gene complex were the most prevalent strains, at 64.7%. In vivo selection of stepwise increase in resistance to vancomycin and teicoplanin was observed in three S. haemolyticus strains serially isolated from a case patient. The results of the present study suggest the regional spread of certain S. haemolyticus clones with diminished susceptibility to glycopeptides, emphasizing the need for continuous monitoring of minimum inhibitory concentration levels of vancomycin and teicoplanin in S. haemolyticus strains, and the importance of infection control practices to prevent its transmission.

Antibiotic resistance patterns of coagulase-negative staphylococcus strains isolated from blood cultures of septicemic patients in Turkey

The aim of this study is to determine antibiotic resistance patterns and slime production characteristics of coagulase-negative Staphylococci (CoNS) caused nosocomial bacteremia. A total of 200 CoNS strains were isolated from blood samples of patients with true bacteremia who were hospitalized in intensive care units and in other departments of Istanbul University Cerrahpasa Medical Hospital between 1999 and 2006. Among 200 CoNS isolates, Staphylococcus epidermidis was the most prevalent species (87) followed by Staphylococcus haemolyticus (23), Staphylococcus hominis (19), Staphylococcus lugdunensis (18), Staphylococcus capitis (15), Staphylococcus xylosus (10), Staphylococcus warneri (8), Staphylococcus saprophyticus (5), Staphylococcus lentus (5), Staphylococcus simulans (4), Staphylococcus chromogenes (3), Staphylococcus cohnii (1), Staphylococcus schleiferi (1), and Staphylococcus auricularis (1). Resistance to methicillin was detected in 67.5% of CoNS isolates. Methicillin-resistant CoNS strains were determined to be more resistant to antibiotics than methicillin-susceptible CoNS strains. Resistance rates of methicillin-resistant and methicillin-susceptible CoNS strains to the antibacterial agents, respectively, were as follows: gentamicin 90% and 17%, erythromycin 80% and 37%, clindamycin 72% and 18%, trimethoprim-sulfamethoxazole 68% and 38%, ciprofloxacin 67% and 23%, tetracycline 60% and 45%, chloramphenicol 56% and 13% and fusidic acid 25% and 15%. None of the strains were resistant to vancomycin and teicoplanin. Slime production was detected in 86 of 200 CoNS strains. Resistance to methicillin was found in 81% of slime-positive and in 57% of slime-negative strains. Our results indicated that there is a high level of resistance to widely used agents in causative methicillin-resistant CoNS strains. However fusidic acid has the smallest resistance ratio, with the exception of glycopeptides. Additionally, most S. epidermidis strains were slime-positive, with statistically significant (p<0.001) association between methicillin resistance and slime production.

Antimicrobial susceptibility of coagulase-negative staphylococci on tissue allografts and isolates from orthopedic patients

Allograft infection occurs at a rate not different from that of similar procedures with large allografts or sterilized prosthetic devices and is usually caused by coagulase-negative staphylococci (CNS). CNS are feared for their limited antimicrobial susceptibility. We aimed at investigating this risk. CNS were isolated from 260 of 1461 allograft tissue grafts and compared with 384 consecutive clinical isolates from a general orthopedic population (258 patients). The CNS were identified and examined for their susceptibility to nine antibiotics used in routine practice. Staphylococcus epidermidis was the most commonly identified (35%) and the most resistant species of the allograft isolates. Comparing the overall antibiotic susceptibility patterns, clinical pathogens were significantly more resistant to six of the nine antibiotics (p < 0.01), namely penicillin, oxacillin, erythromycin, clindamycin, ofloxacin, and gentamicin. In conclusion, massive allograft infection is a well-known life-threatening surgical risk. However, we did demonstrate that allograft-related in contrast to orthopedic clinics-related CNS, are susceptible to commonly used first and second line antibiotics.

Coagulase-negative staphylococcal sepsis in neonates. Association between antibiotic resistance, biofilm formation and the host inflammatory response

BACKGROUND

Coagulase-negative staphylococci (CoNS) are the most prevalent pathogens causing late onset sepsis in neonates. They are often multiresistant to antibiotics, and the ability to form biofilm is considered their main virulence determinant.

METHODS

During a 12-year period, we identified 150 neonates having 164 suspected septic episodes with growth of CoNS in blood culture. We examined the relationship between antibiotic resistance, phenotypic biofilm production and genetic determinants for biofilm formation in different CoNS species and their correlation with neonatal inflammatory response.

RESULTS

Eighty-five episodes were classified as true sepsis, and 79 episodes of CoNS growth in blood culture were considered contaminations. Sixty-one percent of Staphylococcus epidermidis isolates produced biofilm compared with 26% of CoNS non-epidermidis (P < 0.001). We observed no difference in phenotypic biofilm production or genetic determinants for biofilm formation between invasive isolates and contaminants. C-reactive protein levels as a marker of inflammatory response were higher in CoNS sepsis caused by methicillin and aminoglycoside resistant versus susceptible isolates (P = 0.031). In contrast, there was a significant association between a lower C-reactive protein response and biofilm-positive isolates (P = 0.018). Antibiotic resistance was significantly correlated with biofilm production in S. epidermidis, but not in other CoNS species.

CONCLUSIONS

CoNS sepsis with biofilm-forming strains was associated with a decreased host inflammatory response, potentially limiting the immune system to counteract the infection. The impact of antibiotic resistance and virulence determinants on clinical outcome of neonatal CoNS sepsis warrants additional clinical studies.

Survey of nasal colonization by, and assessment of a novel multiplex PCR method for detection of biofilm-forming methicillin-resistant staphylococci in healthy medical students

We surveyed the prevalence of nasal colonization by biofilm-forming methicillin-resistant staphylococci in healthy medical students, who had never had contact with patients, using polymerase chain reaction (PCR) to detect themec A gene, production of penicillin-binding protein 2' (PBP2'), and quantitative assay of biofilm formation on polystyrene. Anterior nasal swabs from 90 students were cultured on mannitol salt and oxacillin salt screening agar plates. In total, 231 staphylococcal isolates belonging to 10 species from 88 students were identified, of which 139 from 77 (88%) students were Staphylococcus epidermidis. The overall prevalences of methicillin-resistant and biofilm-forming staphylococci were 48% (43 of 90) and 59% (53 of 90) for the medical students, respectively. In total 30 (33%) students carried biofilm-forming methicillin-resistant staphylococci in the nares, all of which were identified as S. epidermidis. For rapid detection of biofilm-forming methicillin-resistant S. epidermidis (MRSE), we devised a novel multiplex PCR method to assess a total of 243 staphylococcal isolates, including the 231 isolates from the students. The multiplex PCR assay used six primers to amplify atl E and ica ADB, which are responsible for the biofilm formation ofS. epidermidis, and mec A genes. The multiplex PCR assay revealed that 68 (96%) isolates were detectable in 71 biofilm-forming MRSE isolates, which corresponded to 93% (28 of 30) of biofilm-forming MRSE carriers. Surveillance of nasal colonization with biofilm-forming MRSE using this multiplex PCR in healthcare workers and patients, might provide useful information for the establishment of infection control procedures toward biofilm-forming MRSE.

The ica operon and biofilm production in coagulase-negative Staphylococci associated with carriage and disease in a neonatal intensive care unit

Coagulase-negative staphylococci (CoNS) are a major cause of sepsis in the neonatal intensive care unit (NICU). We evaluated the hypothesis that the ica operon and biofilm production are associated with CoNS disease in this setting. CoNS associated with bacteremia or blood culture contamination and from the skin of infants with CoNS bacteremia or healthy controls were obtained during a prospective case-control study on a busy NICU. A total of 180 strains were identified, of which 122 (68%) were Staphylococcus epidermidis and the remainder were S. capitis (n = 29), S. haemolyticus (n = 11), S. hominis (n = 9), S. warneri (n = 8), and S. auricularis (n = 1). The presence of the genes icaA, icaB, icaC, and icaD was determined by PCR, and biofilm production was examined using qualitative (Congo red agar [CRA]) and quantitative (microtiter plate) techniques. There were no significant differences in the presence of the ica operon or CRA positivity among the four groups of strains. However, quantitative biofilm production was significantly greater in strains isolated from either the blood or the skin of neonates with S. epidermidis bacteremia. We conclude that the quantity of biofilm produced may be associated with the ability to cause CoNS infection. This conclusion suggests that the regulation of biofilm expression may play a central role in the disease process.

The ica operon and biofilm production in coagulase-negative Staphylococci associated with carriage and disease in a neonatal intensive care unit

Coagulase-negative staphylococci (CoNS) are a major cause of sepsis in the neonatal intensive care unit (NICU). We evaluated the hypothesis that the ica operon and biofilm production are associated with CoNS disease in this setting. CoNS associated with bacteremia or blood culture contamination and from the skin of infants with CoNS bacteremia or healthy controls were obtained during a prospective case-control study on a busy NICU. A total of 180 strains were identified, of which 122 (68%) were Staphylococcus epidermidis and the remainder were S. capitis (n = 29), S. haemolyticus (n = 11), S. hominis (n = 9), S. warneri (n = 8), and S. auricularis (n = 1). The presence of the genes icaA, icaB, icaC, and icaD was determined by PCR, and biofilm production was examined using qualitative (Congo red agar [CRA]) and quantitative (microtiter plate) techniques. There were no significant differences in the presence of the ica operon or CRA positivity among the four groups of strains. However, quantitative biofilm production was significantly greater in strains isolated from either the blood or the skin of neonates with S. epidermidis bacteremia. We conclude that the quantity of biofilm produced may be associated with the ability to cause CoNS infection. This conclusion suggests that the regulation of biofilm expression may play a central role in the disease process.

Antimicrobial resistance of coagulase-negative staphylococci from a Kuwait hospital

This study investigated the incidence of antimicrobial resistance in clinically significant coagulase-negative staphylococci at the Mubarak Al Kabeer Hospital, Kuwait. A total of 104 isolates of coagulase-negative staphylococci consisting of S. epidermidis (67), S. haemolyticus (16), S. saprophyticus (6), S. simulans (2), S. hominis (4), S. albus (2), S. sciuri (3), S. warneri (2), S. capitis (1), and S. xylosus (1) were isolated from clinical specimens over a 6-7 month period and tested for resistance to 22 antibacterial agents and the ability to produce slime. They were all susceptible to vancomycin and mupirocin but intermediate resistance to teicoplanin was detected in seven isolates: 83 and 47.7% were resistant to penicillin G and methicillin, respectively, 57% were resistant to gentamicin, 49.5% to erythromycin, 50.4% to tetracycline, and 52.3% to trimethoprim. Resistance to heavy metals and the nucleic-acid binding compound was also detected. More than half of S. epidermidis, S. saprophyticus, S. simulans, S. hominis, and all of S. haemolyticus were multiply resistant to three or more groups of antibiotics and there was a significant association between slime production and resistance to multiple antimicrobial agents in S. epidermidis. The results revealed a high level of resistance to commonly used agents.

Exoprotein and slime production by coagulase-negative staphylococci isolated from goats' milk

Milk from mastitis-free goats from French herds was examined for the presence of coagulase-negative staphylococci (CNS), and 165 positive isolates were evaluated for their capacity to produce exoproteins. Most isolates were identified as Staphylococcus caprae (N = 91) or S. xylosus (N = 36), but members of at least nine other species were present. Overall, some 57% of isolates produced toxins with phenotypic properties of alpha-hemolysin, and 75% produced toxins resembling S. aureus beta and/or delta-hemolysins. Thermostable desoxyribonuclease (TNAse) was secreted by 29% of isolates and thermolabile DNAse by 66%. Slime was produced by 42% of our cultures and, although none of them showed activity to insoluble elastase, over 70% lysed the soluble substrate. No clinical consequences were observed to correlate with exoprotein production, which proved to be inconstant within individual CNS species.

Lack of evidence for increased adherent growth in broth or human serum of clinically significant coagulase-negative staphylococci

The relevance of adherent growth of coagulase-negative staphylococci (CNS) in vitro to their clinical significance is controversial. We have investigated the accumulation on polymer surfaces of clinically significant CNS strains, isolated from blood cultures and intravascular catheter tips, compared with controls. The adherent growth of significant CNS isolates in a microtitre tray assay was not greater than controls, and this finding was repeated when different combinations of target polymer surface, culture medium and incubation atmosphere type were investigated. The surface accumulation of CNS cultured in pooled human serum was poor compared with culture in broth. Whole cell and surface protein profiles of serum grown Staphylococcus epidermidis differed markedly from broth cultured cells. We recommend the use of human body fluids, such as serum, as useful culture media to assess whether potential virulence determinants are likely to be expressed in vivo. The microtitre tray assay of adherent growth is not helpful in determining the virulence of individual CNS isolates.

Regulation of slime production in Staphylococcus epidermidis by iron limitation

Slime production by most strains of Staphylococcus epidermidis was enhanced by conditions of iron limitation produced by the addition of ethylenediamine-di-o-hydroxyphenol acetic acid to the growth medium. The density of the biofilm which formed on the base of microtiter plates was dependent on the degree of iron limitation, the stage of the growth cycle, and the nutritional state of the initial inoculum. One repeatedly slime-negative S. epidermidis strain, passaged in tryptic soya broth containing ethylenediamine-di-o-hydroxyphenol acetic acid, expressed high levels of slime after two passages. These observations suggest that iron limitation is one factor that regulates slime production by S. epidermidis. These findings could explain inconsistencies between the in vivo observation that biofilms invariably form on implanted catheters and the in vitro finding that some isolates from catheter-associated infection fail to produce slime.

Identification of Staphylococcus epidermidis and Staphylococcus hominis from blood cultures by testing susceptibility to desferrioxamine

Testing susceptibility to desferrioxamine has recently been described as a method for the identification of Staphylococcus epidermidis. This method was compared to a commercial test and the tube coagulase test for the identification of staphylococci from blood cultures and other fluid specimens. A total of 216 isolates was tested over a 13-month period. Sensitivity of the desferrioxamine test in identifying isolates of Staphylococcus epidermidis and Staphylococcus hominis was 97.3%, while specificity was 91.8%. When isolates displaying discrepant desferrioxamine results were characterized using recently described interpretive criteria, sensitivity and specificity of the desferrioxamine test improved to 100%. The desferrioxamine test was reliable, inexpensive and simple to perform, and should prove useful in the diagnostic laboratory.

Clinically significant coagulase-negative staphylococci: identification and resistance patterns

Coagulase-negative staphylococci (CNS) of clinical significance, isolated from 131 patients, were investigated during the period 1989-90 in northern Norway. The staphylococci were isolated from blood cultures (68; 51.9%), vascular catheters (6), osteomyelitis foci (13), postoperative and other wounds (15), and urine samples (29). The use of Gram-positive Identification Card (Vitek) and 'Staph-zym' (Rosco) both gave a primarily correct species identification in 95% of the cases. Staphylococcus epidermidis was the predominant species (72.3%). Methicillin-resistance was found in 40 of 131 (30.5%) of all CNS and in 34 of 96 (35.4%) of S. epidermidis. Methicillin-resistant (MR) S. epidermidis strains were usually resistant to gentamicin, tetracycline, chloramphenicol and trimethoprim. MR strains were, however, less resistant to sulphonamides than methicillin-sensitive strains (10 out of 34 vs. 55 out of 62). Methicillin-resistance implied resistance to all beta-lactam antibiotics, including imipenem. Among S. epidermidis, MR isolates increased from 10% in 1987 to 35.4% in 1989-90. All strains were sensitive to vancomycin and rifampicin.

Phage pattern and antibiotic resistance pattern of coagulase-negative staphylococci obtained from immunocompromised patients

A total of 152 coagulase-negative staphylococcal strains were isolated from clinical samples of 14 patients hospitalized after bone-marrow transplantation in a specialized hospital ward in Hungary, during an 18-month period between 1987 and 1989. Two species, Staphylococcus epidermidis and Staphylococcus haemolyticus, predominated (each, 45%). Using Pulverer and co-workers' phage set for typing, 68% of the isolates were typable; 16 phage patterns were observed. A characteristic long pattern with phages Ph10/Ph13/Ph15/U4/U15/U16/U20/U33 /U46 appeared only in S. epidermidis, among 5 of 11 colonized patients (8.5% of all strains). Single lysis with phage Ph13 was observed in 7 of the 14 patients (49% of all strains), in species S. capitis, S. epidermidis, S. haemolyticus, S. hominis, and S. warneri. In S. haemolyticus, non-typable strains predominated (66%); this character occurred only in 2% among other species. The strains colonizing the immunocompromised patients differed from each other in phage pattern, antibiotic resistance pattern, and/or slime production. No hospital infection was suggested. On the other hand, high incidence of two well-definable phage patterns raises some relationship between phage receptors or some regulatory systems in phage multiplication and factors responsible for special colonization as common surface properties.

Observations on coagulase-negative staphylococci in a neonatal unit in India

Fifty neonates were included in a prospective study which determined the frequency of colonization and infection with coagulase-negative staphylococci (CNS) in a neonatal unit. The isolates were characterised by species, antibiotic resistance and ability to produce slime. Twenty-four epidemiologically related isolates (including four isolates from the hands of staff) were also phage typed and had plasmid analysis performed. On the first day of birth, 18% of infants were colonized with CNS, 40% and 30% by days 3-5 and day 7 respectively, and 25% by the 14th day and beyond. Staphylococcus haemolyticus and S. epidermidis were the most frequent CNS species encountered, accounting for 36% and 35% of isolates. Resistance to four or more antibiotics was present in 37% of strains isolated on the first day and this increased to 100% of isolates from infants who stayed for more than 14 days. Forty-five percent of CNS were slime producers; no significant difference was observed in slime producing ability between the species or isolates at different days after birth. Five infants developed septicaemia due to CNS. Staphylococcus haemolyticus and S. epidermidis were recovered as the only pathogens from three and two cases respectively. Detailed typing revealed that one case of infection with S. haemolyticus was preceded by surface colonization with an identical strain. Evidence was also obtained for the transmission of CNS between babies on the hands of staff.

Antibiotic susceptibility of coagulase-negative staphylococcal blood isolates with special reference to adherent, slime-producing Staphylococcus epidermidis strains

The epidemiologic relationship between slime-producing coagulase-negative staphylococci and antibiotic resistance was evaluated by analyzing the in vitro susceptibility of 278 blood isolates to 10 different antimicrobial agents. The strain collection consisted of 60 coagulase-negative staphylococcal septicemia isolates, recovered from at least 2 successive blood cultures from 59 septicemia patients and 218 single blood isolates defined as insignificant. When the slime-producing Staphylococcus epidermidis isolates were compared with all non-slime-producing S. epidermidis isolates, the slime-producing isolates exhibited higher MIC50 and/or MIC90 values than the non-slime-producing isolates, and were also more commonly resistant against many of the antimicrobials tested. The association between slime production and resistance against tobramycin, gentamicin and rifampicin was statistically significant (p less than 0.05). A similar finding was observed among the S. epidermidis septicemia isolates when they were analyzed separately from the single (suspected blood contaminant) S. epidermidis isolates. Further characterization of the septicemia isolates revealed that the positive correlation between slime production and antibiotic resistance reflected, to some extent, multiresistance of 1 epidemic slime-producing S. epidermidis strain. No difference in resistance was observed between the slime-producing and non-slime-producing single S. epidermidis blood isolates.

Slime production by Staphylococcus saprophyticus

Only 9 of 30 Staphylococcus saprophyticus strains produced slime in trypticase soy broth, while all did so in urine. It was found that urea was essential for the production of slime. The pH, the iron concentration, or the presence of sex hormones did not affect slime production.

Adherence measured by microtiter assay as a virulence marker for Staphylococcus epidermidis infections

Staphylococcus epidermidis strains isolated from clinical sources showed a wide range of abilities to adhere to glass and plastic materials. The degree of adherence depended on a number of factors, most notably, the composition of the growth medium. Adherence was enhanced by the addition of glucose or oleic acid to the growth medium and inhibited by serum. We have demonstrated a statistically significant association between the quantitative assessment of adherence to polystyrene tissue culture plates and clinical relevance. No such association was found when adherence was assessed by the qualitative adherence assay. Possible new approaches for assessing the clinical relevance of coagulase-negative staphylococcal isolates are discussed.

Temporal study of staphylococcal species on the skin of human subjects in isolation and clonal analysis of Staphylococcus capitis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis

The staphylococcal skin floras of an isolated group of subjects were studied for 1 year. A wide variation in isolation patterns was found for different species. Staphylococcus intermedius, previously thought to be of veterinary origin, was found to be part of the resident flora of some subjects, and this may indicate a wider role for it in clinical infection. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of S. capitis isolates indicated persistent skin colonization at some sites; each region was colonized by only one clone of that species, although an adjacent area could be inhabited by a separate clone. Nine clonal groups were identified by SDS-PAGE; there was a degree of specialization between the groups with regard to the sites which they colonized. The interaction between species at a single site was less well defined. Noncolonizing isolates often exhibited phenotypic similarities that were lower than expected when compared with their presumed source. The results of SDS-PAGE analysis were compared with immunoblotting, antibiograms, and biotyping, and SDS-PAGE analysis was found to be a useful and practical tool for epidemiological work.

The acquisition of antibiotic resistant coagulase-negative staphylococci by aortic graft recipients

The staphylococcal flora of the groin and perianal area was studied in 12 patients undergoing aortic grafts and 3 patients having repair of ventral abdominal hernias. A total of 892 isolates of coagulase-negative staphylococci (CNS) were identified and their antibiotic resistance determined. The species most frequently isolated were S. epidermidis and S. haemolyticus with the latter showing the highest incidence of antibiotic resistance. Five of 15 patients had CNS resistant to methicillin and gentamicin on admission. The effect of pre-operative bathing with chlorhexidine was studied in 6 patients and appeared to reduce the acquisition of multi-resistant CNS in the week after operation.

Effects of extracellular products from Staphylococcus saprophyticus on human lymphocytes

Extracellular products from Staphylococcus saprophyticus were isolated and tested for their effect on the lymphoproliferative activity of con A and LPS and on the growth of human lymphocytes. The stimulatory effects of con A or LPS were not affected but a T-cell mitogenic activity was noted after 5 days of incubation. The extracellular material was separated by gel chromatography and the mitogenic activity was shown to be located to the protein fraction.

Characterization of coagulase-negative staphylococci by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analyses

Coagulase-negative staphylococci are important nosocomial pathogens. At present, no wholly satisfactory typing scheme exists for these organisms. Therefore, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting were assessed as characterization methods. A total of 100 type strains and nontyped isolates representing nine species of coagulase-negative staphylococci were analyzed. Each species had a reproducible, characteristic whole-cell banding pattern when analyzed by either method. These species-specific profiles were obtained for all isolates despite disparate geographical origins and clinical isolation sites. Intraspecies similarities, calculated by using the Dice coefficient, were significantly higher than interspecies similarities. Although some species were more heterogeneous than others, the allocation of isolates to any particular species was reinforced by the high degree of interspecies dissimilarity. Application of SDS-PAGE also distinguished discrete subspecies groups. These groups possessed the characteristic profile of their species but were distinguished by a group of variable polypeptides. Species-specific banding patterns were also obtained by immunoblotting of whole-cell polypeptides. Differences between immunoblot and SDS-PAGE profiles could be attributed to variations of antigenicity of particular polypeptides. However, both SDS-PAGE and immunoblotting provided reproducible and sensitive methods for characterization of coagulase-negative staphylococci. Standardization of these techniques could provide the basis for a primary typing scheme.

Prevalence of peritonitis-associated coagulase-negative staphylococci on the skin of continuous ambulatory peritoneal dialysis patients

The predominance of coagulase-negative staphylococci as normal skin flora is thought to be a factor in their association with episodes of peritonitis in patients undergoing continuous ambulatory peritoneal dialysis. We investigated the prevalence of peritonitis-associated strains on the skin of 28 patients undergoing peritoneal dialysis. Coagulase-negative staphylococci were the most frequently isolated organisms, comprising 47% of peritoneal dialysis fluid isolates and 59% of body site isolates. A total of 142 coagulase-negative staphylococci were speciated, tested for their antimicrobial sensitivity and slime production, and identified by phage typing and plasmid-profile analysis. Staphylococcus epidermidis was the most commonly identified species from both peritoneal dialysis fluid (73%) and body sites (53%). Multiple antibiotic resistance was common, and the greater proportion of isolates were resistant to methicillin; 63.6% of peritoneal dialysis fluid isolates and 61.7% of body-site isolates. S. haemolyticus isolates were significantly more resistant to methicillin than other species. By phage typing and plasmid-profile analysis it was shown that peritonitis was rarely caused by skin-colonizing strains. In only 3 of 14 patients were peritonitis-associated strains isolated as skin colonizers, and no patients developed peritonitis due to organisms previously isolated as skin colonizers.