Isolation of methicillin-resistant coagulase-negative staphylococci from patients undergoing continuous ambulatory peritoneal dialysis (CAPD) and comparison of different molecular techniques for discriminating isolates of Staphylococcus epidermidis

Molecular Detection and Characterization of the Staphylococcus epidermidis and Staphylococcus haemolyticus Isolated from Hospitalized Patients and Healthcare Workers in Iran

Background

The present study is aimed at surveying the antibiotics resistance profile, biofilm formation ability, staphylococcal cassette chromosome mec (SCCmec) types, and molecular epidemiology of Staphylococcus epidermidis and Staphylococcus haemolyticus isolated from hospitalized patients and healthcare workers in four teaching hospitals in Iran.

Methods

In total, 43 Staphylococcus epidermidis and 12 Staphylococcus haemolyticus were isolated from hospitalized patients, and 19 Staphylococcus epidermidis and 7 Staphylococcus haemolyticus isolated from healthcare workers were included in the present study. The antimicrobial resistance profile of isolates was determined using the disk diffusion method. Moreover, the resistance of isolates to methicillin was identified using the cefoxitin disk diffusion test. The microtiter-plate test was used for quantifying biofilm formation. Moreover, the frequency of icaA and icaD genes was determined using PCR assay. The molecular epidemiology of methicillin-resistant isolates was determined using SCCmec typing and pulsed-field gel electrophoresis methods.

Results

Among all coagulase-negative staphylococci isolates, the highest resistance rate (81.5%) was seen for cefoxitin and cotrimoxazole. All of the isolates were susceptible to linezolid. Out of the 66 mecA-positive isolates, the most common SCCmec type was the type I (n = 23; 34.8%) followed by type IV (n = 13; 19.7%). Using pulsed-field gel electrophoresis (PFGE) assay, 27 PFGE types including 14 common types and 13 singletons were obtained among 51 methicillin-resistant S. epidermidis (MRSE) isolates. Moreover, among 12 methicillin-resistant S. haemolyticus (MRSH) isolates, 8 PFGE types were detected, of which 5 PFGE types were singletons.

Conclusion

The high rate of resistance to antibiotics as well as the possibility of cross-infection shows the importance of a pattern shift in the management and controlling programs of coagulase-negative staphylococci, especially in healthcare centers. Clinical trial registration. The present study is not a clinical trial study. Thus, a registration number is not required.

Virulence Factors in Coagulase-Negative Staphylococci

Coagulase-negative staphylococci (CoNS) have emerged as major pathogens in healthcare-associated facilities, being S. epidermidis, S. haemolyticus and, more recently, S. lugdunensis, the most clinically relevant species. Despite being less virulent than the well-studied pathogen S. aureus, the number of CoNS strains sequenced is constantly increasing and, with that, the number of virulence factors identified in those strains. In this regard, biofilm formation is considered the most important. Besides virulence factors, the presence of several antibiotic-resistance genes identified in CoNS is worrisome and makes treatment very challenging. In this review, we analyzed the different aspects involved in CoNS virulence and their impact on health and food.

Higher accuracy of genotypic identification compared to phenotyping in the diagnosis of coagulase-negative staphylococcus infection in orthopedic surgery

PURPOSE

To determine whether Repetitive Extragenic Palindromic PCR (rep-PCR) genotyping can improve the diagnosis of coagulase-negative staphylococcal (CoNS) orthopaedic infections in comparison to phenotyping.

METHODS

Prospective study comparing the results of phenotypic/genotypic (rep-PCR) testing in patients with suspected CoNS infection. Each strain was analysed using both methods. Strains identified as identical in ≥2 samples were considered as pathogenic.

RESULTS

255 CoNS strains from 52 surgical episodes were included. Infection was diagnosed by phenotyping in 38(73%) cases and by genotyping in 40(77%). The Kappa index was 0.59. Sensitivity, Specificity, Positive Predictive Value (PPV) and Negative Predictive Value (NPV) for phenotyping (vs. rep-PCR) were: 88%, 75%, 92%, and 64%. 5/14(36%) of cases not considered as true infections by phenotyping were diagnosed as infections with genotyping. In a subgroup of 203 strains from 41 surgical procedures with orthopaedic implants, the kappa index was 0.68. Sensitivity, Specificity, PPV, and NPV for phenotyping were: 93%, 73%, 90% and 80%. Again, 2/10 episodes in which CoNS were considered non-infective by phenotyping were diagnosed as infected by genotyping.

CONCLUSIONS

Rep-PCR genotyping can identify identical CoNS strains that differ in their phenotype and should be used as a complementary technique. One-third of infected cases may be misdiagnosed without genotypic analysis.

Staphylococcal cassette chromosome mec typing and mecA sequencing in methicillin-resistant staphylococci from Algeria: a highly diversified element with new mutations in mecA

Genetic mechanisms of methicillin resistance are still relevant in staphylococci. The aims of this study are to assess the possible exchanges of staphylococcal cassette chromosome mec (SCCmec) among isolates of methicillin-resistant staphylococci (MRS) and to check for known or new mutations in mecA DNA. A total of 35 MRS non-repetitive isolates were recovered, including 20 Staphylococcushaemolyticus, 7 Staphylococcusaureus, 4 Staphylococcussciuri, 2 Staphylococcussaprophyticus and 1 isolate each of Staphylococcusxylosus and Staphylococcuslentus. Only 16 of the 35 strains were assigned to known SCCmec types: 7 SCCmec VII, 6 SCCmec IV and 3 SCCmec III, with possible horizontal transfer of the SCCmec VII from methicillin-resistant S. haemolyticus to methicillin-susceptible S. aureus. mecA gene sequencing in ten selected isolates allowed description of nine punctual mutations, seven of which were reported for the first time. The most frequent mutation was G246E, identified in isolates of methicillin-resistant S. aureus, S. sciuri, S. saprophyticus and S. lentus. These results emphasized the high degree of genetic diversity of SCCmec element in MRS and describe new missense mutations in mecA, which might be important in understanding the evolution of methicillin and new β-lactam resistance.

Molecular epidemiology of coagulase-negative Staphylococcus carriage in neonates admitted to an intensive care unit in Brazil

Background

Nasal colonization with coagulase-negative Staphylococcus (CoNS) has been described as a risk factor for subsequent systemic infection. In this study, we evaluated the genetic profile of CoNS isolates colonizing the nares of children admitted to a neonatal intensive care unit (NICU).

Methods

We assessed CoNS carriage at admittance and discharge among newborns admitted to a NICU from July 2007 through May 2008 in one of the major municipalities of Brazil. Isolates were screened on mannitol salt agar and tryptic soy broth and tested for susceptibility to antimicrobials using the disc diffusion method. Polymerase chain reaction (PCR) was used to determine the species, the presence of the mecA gene, and to perform SCCmec typing. S. epidermidis and S. haemolyticus isolated from the same child at both admission and discharge were characterized by PFGE.

Results

Among 429 neonates admitted to the NICU, 392 (91.4%) had nasal swabs collected at both admission and discharge. The incidence of CoNS during the hospitalization period was 55.9% (95% confidence interval [CI]: 50.9-60.7). The most frequently isolated species were S. haemolyticus (38.3%) and S.epidermidis (38.0%). Multidrug resistance (MDR) was detected in 2.2% and 29.9% of the CoNS isolates, respectively at admittance and discharge (p = 0.053). The mecA gene was more prevalent among strains isolated at discharge (83.6%) than those isolated at admission (60%); overall, SCCmec type I was isolated most frequently. The length of hospitalization was associated with colonization by MDR isolates (p < 0.005). Great genetic diversity was observed among S. epidermidis and S. haemolyticus.

Conclusions

NICU represents an environment of risk for colonization by MDR CoNS. Neonates admitted to the NICU can become a reservoir of CoNS strains with the potential to spread MDR strains into the community.

Antistaphylococcal activity of bacteriophage derived chimeric protein P128

Background

Bacterial drug resistance is one of the most significant challenges to human health today. In particular, effective antibacterial agents against methicillin-resistant Staphylococcus aureus (MRSA) are urgently needed. A causal relationship between nasal commensal S. aureus and infection has been reported. Accordingly, elimination of nasal S. aureus reduces the risk of infection. Enzymes that degrade bacterial cell walls show promise as antibacterial agents. Bacteriophage-encoded bacterial cell wall-degrading enzymes exhibit intrinsic bactericidal activity. P128 is a chimeric protein that combines the lethal activity of the phage tail-associated muralytic enzyme of Phage K and the staphylococcal cell wall targeting-domain (SH3b) of lysostaphin.

Here we report results of in vitro studies evaluating the susceptibility of staphylococcal strains to this novel protein.

Results

Using the broth microdilution method adapted for lysostaphin, we found that P128 is effective against S. aureus clinical strains including MRSA, methicillin-sensitive S. aureus (MSSA), and a mupirocin-resistant S. aureus. Minimum bactericidal concentrations and minimum inhibitory concentrations of P128 (1-64 μg/mL) were similar across the 32 S. aureus strains tested, demonstrating its bactericidal nature.

In time-kill assays, P128 reduced colony-forming units by 99.99% within 1 h and inhibited growth up to 24 h.

In an assay simulating topical application of P128 to skin or other biological surfaces, P128 hydrogel was efficacious when layered on cells seeded on solid media. P128 hydrogel was lethal to Staphylococci recovered from nares of healthy people and treated without any processing or culturing steps, indicating its in situ efficacy. This methodology used for in vitro assessment of P128 as an agent for eradicating nasal carriage is unique.

Conclusions

The novel chimeric protein P128 is a staphylococcal cell wall-degrading enzyme under development for clearance of S. aureus nasal colonization and MRSA infection. The protein is active against globally prevalent antibiotic-resistant clinical isolates and other clinically significant staphylococcal species including S. epidermidis. The P128 hydrogel formulation was bactericidal against Staphylococci including S. aureus recovered from the nares of 31 healthy people, demonstrating its in situ efficacy.

Double triplex real-time PCR assay for simultaneous detection of Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus hominis, and Staphylococcus haemolyticus and determination of their methicillin resistance directly from positive blood culture bottles

We developed and validated here a double triplex real-time PCR assay to simultaneously detect and identify Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus hominis, Staphylococcus haemolyticus and their methicillin resistance in a single reaction directly from Gram-positive cocci-in-clusters (GPCs)-positive blood culture bottles. From August 15, 2009 through February 15, 2010, 238 GPC-positive samples were collected and identified by conventional methods as 11 methicillin-resistant S. aureus (MRSA), 28 methicillin-susceptible S. aureus (MSSA), 176 MR coagulase-negative staphylococci (MRCoNS), 21 MSCoNS and two Enterococcus faecalis. The double triplex real-time PCR assay was targeted and detected tuf, nuc and mecA genes in the first tube and atlE, gap and mvaA genes in the second tube which could be run simultaneously. The detection limit of the assay was found at 10(3) CFU/ml for the atleE gene, 10(4) CFU/ml for the mva gene and 10(5) CFU/ml for gap, nuc, mecA and tuf genes based on seeding experiments. All Staphylococcus species except two S. epidermidis were correctly identified by the assay. The double triplex real-time PCR assay quickly and accurately detects S. aureus, S. epidermidis, S. hominis and S. haemolyticus and their methicillin resistance in a single reaction directly from positive blood culture bottles within 83 min.

Prevalence and characteristics of methicillin-resistant coagulase-negative staphylococci from livestock, chicken carcasses, bulk tank milk, minced meat, and contact persons

Background

Methicillin-resistant coagulase-negative staphylococci (MR-CNS) are of increasing importance to animal and public health. In veterinary medicine and along the meat and milk production line, only limited data were so far available on MR-CNS characteristics. The aim of the present study was to evaluate the prevalence of MR-CNS, to identify the detected staphylococci to species level, and to assess the antibiotic resistance profiles of isolated MR-CNS strains.

Results

After two-step enrichment and growth on chromogenic agar, MR-CNS were detected in 48.2% of samples from livestock and chicken carcasses, 46.4% of samples from bulk tank milk and minced meat, and 49.3% of human samples. Using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), 414 selected MR-CNS strains belonged to seven different species (S. sciuri, 32.6%; S. fleurettii, 25.1%; S. haemolyticus, 17.4%; S. epidermidis, 14.5%, S. lentus, 9.2%; S. warneri, 0.7%; S. cohnii, 0.5%). S. sciuri and S. fleurettii thereby predominated in livestock, BTM and minced meat samples, whereas S. epidermidis and S. haemolyticus predominated in human samples. In addition to beta-lactam resistance, 33-49% of all 414 strains were resistant to certain non-beta-lactam antibiotics (ciproflaxacin, clindamycin, erythromycin, tetracycline).

Conclusions

A high prevalence of MR-CNS was found in livestock production. This is of concern in view of potential spread of mecA to S. aureus (MRSA). Multiresistant CNS strains might become an emerging problem for veterinary medicine. For species identification of MR-CNS isolated from different origins, MALDI-TOF MS proved to be a fast and reliable tool and is suitable for screening of large sample amounts.

Prevalence, aetiology and antibiotic resistance profiles of coagulase negative staphylococci isolated in a teaching hospital

In this paper we carried out a study about prevalence of the clinically significant coagulase negative staphylococcal (CNS) isolates found in an university hospital. Two hundred four CNS isolates from 191 patients obtained between the period of 1998 to 2002, were studied. About 27% (52/191) of the infection cases studied were confirmed as CNS-associated diseases. Blood stream infection (BSI) was the most frequent CNS associated-disease (25%; 13/52). The great majority of the BSI was verified in the Neonatal Intensive Care Unit (NICU). The analysis of the 52 patients medical history showed that 85% of the BSI was acquired in hospital. Most of the CNS nosocomial infections were associated with the use of indwelling medical devices. The incidence of methicillin-resistance among significant CNS isolates was 38%. In this study, a high percentage of exogenous contaminant was verified (60%), indicating that contamination of clinical specimens during sample collection is critical.

Antimicrobial resistance and molecular characterization of Staphylococcus haemolyticus in a Chinese hospital

The aim of this study was to perform the molecular characterization of methicillin-resistant Staphylococcus haemolyticus (MRSH) from clinical specimens of patients in a Chinese hospital. One hundred and thirty-three strains of S. haemolyticus collected from April 2002 to April 2003 were analyzed. Antimicrobial susceptibility to 15 antimicrobial agents was determined by the broth microdilution method. The resistant rates to penicillin G and oxacillin were higher than 90%. There were no isolates resistant to linezolid or vancomycin, and only 6.0% of the strains were resistant to teicoplanin. The positivity rate for mecA genes was 90.2% by polymerase chain reaction (PCR). Ninety MRSH (isolated from inpatients and mecA-gene-positive) were genotyped by pulsed-field gel electrophoresis (PFGE) after SmaI digestion. Twenty-five different PFGE patterns (A approximately Y) were found and a major clone (type A; n = 36) with five subtypes was identified. Clone A was detected during a 1-year period. Identical PFGE types were found in different wards and patients. The results of this study suggest the clonal spread of MRSH within our hospital. This emphasizes the need for control and prevention measures.

Antimicrobial Activity and Chemical Composition of Senecio Sandrasicus on Antibiotic Resistant Staphylococci

The antimicrobial activity of hexane, chloroform, ethyl acetate and ethanol extracts of the aerial parts of S. sandrasicus P.H. Davis ( Asteraceae), endemic to Sandras mountain (Turkey), were determined. The antimicrobial activity of the extracts on microorganisms including multi-resistant staphylococci were evaluated using the disc diffusion method. The strains of multi-resistant staphylococci and the other standart bacteria were inhibited by some extracts. The volatile organic compouds of S. sandrasicus was determined by Gas Chromatography (GC) and Gas Chromatography-Mass Spectrometry (GC-MS). The major compounds of hexane extract were aromadendrene oxide 2 (13.3%), spathulenol (12.5%) and β-caryophylene (11.8%), respectively.

Coagulase negative staphylococcal peritonitis in peritoneal dialysis patients: review of 232 consecutive cases

BACKGROUND AND OBJECTIVES

Coagulase-negative Staphylococcus species is the most common cause of peritoneal dialysis-related peritonitis; however, the optimal treatment strategy of coagulase-negative Staphylococcus species peritonitis remains controversial.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

All of the coagulase-negative Staphylococcus species peritonitis in a dialysis unit from 1995 to 2006 were reviewed. During this period, there were 2037 episodes of peritonitis recorded; 232 episodes (11.4%) in 155 patients were caused by coagulase-negative Staphylococcus species.

RESULTS

The overall primary response rate was 95.3%; the complete cure rate was 71.1%. Patients with a history of recent hospitalization or recent antibiotic therapy had a higher risk for developing methicillin-resistant strains. Episodes that were treated initially with cefazolin or vancomycin had similar primary response rate and complete cure rate. There were 33 (14.2%) episodes of relapse and 29 (12.5%) episodes of repeat peritonitis; 12 (60.6%) of the repeat episodes developed within 3 mo after completion of antibiotics. Relapse or repeat episodes had a significantly lower complete cure rate than the other episodes. For relapse or repeat episodes, treatment with effective antibiotics for 3 wk was associated with a significantly higher complete cure rate than the conventional 2-wk treatment.

CONCLUSIONS

Coagulase-negative Staphylococcus species peritonitis remains a common complication of peritoneal dialysis. Methicillin resistance is common, but the treatment outcome remains favorable when cefazolin is used as the first-line antibiotic. A 3-wk course of antibiotic can probably achieve a higher cure rate in relapse or repeat episodes.

Comparison of molecular typing methods for characterization of Staphylococcus epidermidis: proposal for clone definition

In the present study we give some direction on the selection of the most appropriate typing method(s) to be used for the characterization of Staphylococcus epidermidis, in view of the most recent findings on the evolution, population structure, and epidemiology of this species. In order to achieve this aim, quantitative assessment of the correlation of the results of three typing methods--pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and staphylococcal chromosomal cassette mec (SCCmec) typing, which target different regions of the chromosome that evolve at different rates--was performed. In order to evaluate the discriminatory ability and the strength and direction of the correlation of the different typing methods, Simpson's index of diversity (SID), the adjusted Rand coefficient (AR), and the Wallace coefficient (W) were calculated. PFGE was the most discriminatory method (SID = 99%), followed by MLST (SID = 90%) and SCCmec typing (SID = 75%). The values of AR and W (0.10 < AR < 0.30; 0.50 < W < 0.75) indicated that the partition of the same isolate collection by PFGE, MLST, and SCCmec typing provided results that had only a poor correlation with each other. However, the information provided by the combination of PFGE and SCCmec enabled the prediction of the results obtained by MLST at the level of the clonal complex with a high degree of precision (W > 0.90). We propose that clones of S. epidermidis be defined by the combination of the PFGE type followed by the SCCmec type, which provides reliable information on the short-term epidemiology and the ability to predict with consistency long-term clonal evolution.

Inferring a population structure for Staphylococcus epidermidis from multilocus sequence typing data

Despite its importance as a human pathogen, information on population structure and global epidemiology of Staphylococcus epidermidis is scarce and the relative importance of the mechanisms contributing to clonal diversification is unknown. In this study, we addressed these issues by analyzing a representative collection of S. epidermidis isolates from diverse geographic and clinical origins using multilocus sequence typing (MLST). Additionally, we characterized the mobile element (SCCmec) carrying the genetic determinant of methicillin resistance. The 217 S. epidermidis isolates from our collection were split by MLST into 74 types, suggesting a high level of genetic diversity. Analysis of MLST data using the eBURST algorithm revealed the existence of nine epidemic clonal lineages that were disseminated worldwide. One single clonal lineage (clonal complex 2) comprised 74% of the isolates, whereas the remaining isolates were clustered into 8 minor clonal lineages and 13 singletons. According to our evolutionary model, SCCmec was acquired at least 56 times by S. epidermidis. Although geographic dissemination of S. epidermidis strains and the value of the index of association between the alleles, 0.2898 (P < 0.05), support the clonality of S. epidermidis species, examination of the sequence changes at MLST loci during clonal diversification showed that recombination gives rise to new alleles approximately twice as frequently as point mutations. We suggest that S. epidermidis has a population with an epidemic structure, in which nine clones have emerged upon a recombining background and evolved quickly through frequent transfer of genetic mobile elements, including SCCmec.

Commensal isolates of methicillin-resistant Staphylococcus epidermidis are also well equipped to produce biofilm on polystyrene surfaces

OBJECTIVES

To study biofilm production and to detect icaAD, atlE and aap genes in 137 isolates of methicillin-resistant Staphylococcus epidermidis (MRSE) obtained from healthy individuals from the community (35 isolates), from hospitalized patients at the Antônio Pedro University Hospital (25 isolates) and from individuals from a home-care system (HCS; 77 isolates).

METHODS

Biofilm production was determined in vitro using polystyrene inert surfaces. icaAD, atlE and aap genes were detected using PCR. Hybridization experiments were also carried out to confirm some PCR results. Antimicrobial susceptibility testing was carried out using the NCCLS methods.

RESULTS

Although many of the commensal MRSE isolates produced biofilms, the percentage of biofilm producers was significantly higher (P = 0.0107) among hospital isolates (76%) than among isolates from the community (60%) and from the HCS (57%). An association was observed between multiresistance and biofilm production for isolates obtained from healthy individuals from the community and from household contacts from the HCS (P < 0.0001). The concomitant presence of the ica operon and atlE and aap genes was associated with the strong biofilm-producer phenotype (P < 0.0001).

CONCLUSION

Because many of the commensal MRSE isolates obtained from nares produced biofilms and carried icaAD, aap and atlE genes, biofilms or such genetic elements should not be used as markers for clinical significance. The biofilm environment seems to increase genetic exchanges and hence may contribute to multiresistance phenotypes.

The investigation of Staphylococcus aureus and coagulase-negative staphylococci nasal carriage among patients undergoing haemodialysis

The frequency of nasal staphylococcal colonization among haemodialysed patients was investigated. The swabs were collected in 1998 and 2004 from 28 and 43 patients, respectively. Staphylococcus aureus colonization rates were 57.1% and 27.9% in 1998 and 2004, respectively. Twenty-six coagulase-negative staphylococci (CNS) isolates were cultured: S. epidermidis (21), S. lugdunensis (2), single S. haemolyticus, S. warneri, and S. capitits isolates. One S. aureus and 10 CNS isolates were methicillin resistant. The methicillin-resistant S. aureus (MRSA) was resistant to beta-lactams, tetracycline, and harbored the pvl gene encoding the Panton-Valentine leukocidin. The decrease in S. aureus colonization at 6-year interval was observed. The presence of the pvl gene and a favorable antibiotic susceptibility pattern of the MRSA suggest that the isolate was a member of community-acquired MRSA (CA-MRSA). Concluding, screening of haemodialysed patients for staphylococcal colonization accompanied by characterization of cultured isolates is important to understand its epidemiology and to develop infection prevention measures and treatment strategies.

RAPD for the typing of coagulase-negative staphylococci implicated in catheter-related bloodstream infection

OBJECTIVES

A rapid random amplification of polymorphic DNA (RAPD) technique was developed to distinguish between strains of coagulase-negative staphylococci (CoNS) involved in central venous catheter (CVC)-related bloodstream infection. Its performance was compared with that of pulsed-field gel electrophoresis (PFGE).

METHODS

Patients at the University Hospital Birmingham NHS Foundation Trust, U.K. who underwent stem cell transplantation and were diagnosed with CVC-related bloodstream infection due to CoNS whilst on the bone marrow transplant unit were studied. Isolates of CoNS were genotyped by PFGE and RAPD, the latter employing a single primer and a simple DNA extraction method.

RESULTS

Both RAPD and PFGE were highly discriminatory (Simpson's diversity index, 0.96 and 0.99, respectively). Within the 49 isolates obtained from blood cultures of 33 patients, 20 distinct strains were identified by PFGE and 25 by RAPD. Of the 25 strains identified by RAPD, nine clusters of CoNS contained isolates from multiple patients, suggesting limited nosocomial spread. However, there was no significant association between time of inpatient stay and infection due to any particular strain.

CONCLUSION

The RAPD technique presented allows CoNS strains to be genotyped with high discrimination within 4h, facilitating real-time epidemiological investigations. In this study, no single strain of CoNS was associated with a significant number of CVC-related bloodstream infections.

Genetic Diversity among Methicillin-ResistantStaphylococcus epidermidis(MRSE)

We selected 106 methicillin-resistant Staphylococcus epidermidis (MRSE) and 22 methicillin-susceptible S. epidermidis (MSSE) hospital isolates--each with a different PFGE pattern--for more detailed documentation of genetic diversity. The 106 MRSE isolates showed extensive variation in the SmaI DNA fragments hybridizing with the DNA probe for mecA, the molecular size of which varied from as low as 20 kb up to over 500 kb. Parallel variation was also observed in the size of DNA fragments hybridizing with the chromosomal genes orfX and gyrA, and this was also observed in MSSE isolates. In contrast, SmaI fragments associated with the housekeeping genes murE and aroE, both located distantly from orfX, showed little size variation. Typing for the mec complex and ccr identified 10 different SCCmec structures and a large number of strains (21 isolates) that were non-typeable. The majority of strains studied (36%) carried a SCCmec type IV-like structure, including strains with non-related PFGE profiles. On the other hand, closely related strains often carried different types of SCCmec. The findings indicate that the acquisition and/or loss of mobile genetic elements, including various structural types of SCCmec, may occur frequently in the vicinity of the orfX gene on the S. epidermidis chromosome.