Specific detection of methicillin-resistant Staphylococcus species by multiplex PCR.

In Staphylococcus aureus, mecA and femA are the genetic determinants of methicillin resistance. By using a multiplex PCR strategy, 310- and 686-bp regions of the mecA and femA genes, respectively, were coamplified to identify susceptible (lacking mecA) and resistant (mecA+) staphylococci and to differentiate S. aureus (femA+) from coagulase-negative staphylococci (lacking femA). A third staphylococcal genomic sequence, corresponding to IS431 and spanning 444 bp, was used as a PCR control. One hundred sixty-five staphylococcal strains were tested. All 72 methicillin-resistant strains were found to be mecA+, and 92 of the 93 susceptible isolates lacked mecA. Only one coagulase-negative Staphylococcus isolate carrying the mecA gene was highly susceptible to oxacillin. The femA determinant was a unique feature of S. aureus; it was found in 100% of the S. aureus strains tested but was undetectable in all of the coagulase-negative staphylococci tested. The possibility of directly detecting the mecA and femA genes in blood samples was also investigated. After two amplification steps, a sensitivity of 50 microorganisms per ml of freshly collected spiked blood was achieved. In conclusion, coamplification of mecA and femA determinants proved to be very reliable both for rapid detection of methicillin resistance and differential diagnosis between S. aureus and other staphylococci. This technique, which can be successfully performed with blood samples, could be a useful tool in the diagnosis and treatment monitoring of staphylococcal infections.     

Isolation of methicillin-resistant coagulase-negative staphylococci from chickens.

Methicillin-resistant coagulase-negative staphylococci were isolated from the nares and skin of 1- to 8-week-old healthy chickens in three flocks from a farm. Isolation of methicillin-resistant coagulase-negative staphylococci was positive for 72 (25.7%) of the 280 chickens tested, with the frequency varying from 2.2 to 100% according to flock. A total of 45 appropriate isolates were selected and subjected to identification. Of the 45 methicillin-resistant coagulase-negative staphylococcal isolates selected, 37 were identified as Staphylococcus sciuri, 5 were identified as Staphylococcus epidermidis, and 3 were identified as Staphylococcus saprophyticus. The distribution of the species was different among the flocks. Comparative analysis of the SmaI-digested chromosomal DNA by pulsed-field gel electrophoresis revealed that the isolates could have originated from a single clone of each of S. sciuri and S. saprophyticus and three clones of S. epidermidis. By two methods based on the PCR technique, the mecA gene was detected in all five representative isolates of each methicillin-resistant coagulase-negative staphylococcal clone. The nucleotide sequence of a PCR fragment obtained from an isolate of S. sciuri was completely identical to the corresponding region of mecA genes reported in human methicillin-resistant Staphylococcus aureus isolates and Staphylococcus epidermidis isolates. The representative methicillin-resistant coagulase-negative staphylococcal isolates were resistant to many beta-lactam antibiotics, and some isolates were also resistant to macrolide and aminoglycoside antibiotics. This is the first evidence of the existence of methicillin-resistant coagulase-negative staphylococci from animals possessing the mecA gene.     

Identification of methicillin-resistant strains of staphylococci by polymerase chain reaction.

A simple and reliable method using a polymerase chain reaction (PCR) was devised to identify methicillin-resistant staphylococci. By using lysates of the strain to be tested as templates and 22-mer oligonucleotides as primers, a 533-bp region of mecA, the structural gene of a low-affinity penicillin-binding protein (PBP 2'), was amplified by PCR and detected by agarose gel electrophoresis. Results obtained by this method were compared with those obtained by broth microdilution MIC determination for 210 and 100 clinical isolates of Staphylococcus aureus and coagulase-negative staphylococci, respectively. Of 99 mecA-negative S. aureus isolates, 100% of the strains were methicillin susceptible and 98% of the strains were oxacillin susceptible. Three strains (3%) of 111 mecA-positive S. aureus isolates exhibited almost the same susceptibility to beta-lactams as the mecA-negative ones and did not produce detectable amounts of PBP 2' despite the presence of the mecA gene. One of them yielded typically methicillin-resistant variants at a low frequency with concomitant recovery of PBP 2' production. The mecA gene was also found in coagulase-negative Staphylococcus epidermidis, Staphylococcus haemolyticus, Staphylococcus sciuri, Staphylococcus saprophyticus, and Staphylococcus caprae and conferred resistance on most of the bacteria.     

Rapid detection of the mecA gene in methicillin-resistant staphylococci by enzymatic detection of polymerase chain reaction products.

In order to identify methicillin-resistant staphylococci from clinical sources with ease and reliability, enzymatic detection of polymerase chain reaction (ED-PCR) was applied. ED-PCR is based on the capture of amplified products via biotin-streptavidin affinity and the detection of an incorporated hapten in amplified products with an enzyme-linked antibody. In order to identify methicillin-resistant staphylococci of all species, a 150-bp fragment of the mecA gene was targeted for ED-PCR. After PCR was performed with a pair of biotin and dinitrophenol 5'-labeled primers, the reaction mixture was applied to a microtiter well precoated with streptavidin. Thereafter, bound PCR products were detected colorimetrically with alkaline phosphatase-conjugated anti-dinitrophenol antibody. The extraction of DNA from staphylococcal cells for PCR was simplified so that it could be performed within one tube. The total assay, including PCR, took less than 3 h. The sensitivity of mecA gene detection ranged from greater than 5 x 10(2) CFU per tube for Staphylococcus aureus to greater than 5 x 10(3) CFU per tube for Staphylococcus epidermidis. Genotyping results obtained by ED-PCR of 161 tested strains from the colonies (97 strains of S. aureus and 64 strains of coagulase-negative staphylococci) were compared with the phenotypic susceptibilities of the strains to oxacillin. The results of ED-PCR showed excellent agreement with the MICs of oxacillin with very few exceptions; only one strain of S. aureus and two strains of coagulase-negative staphylococci were found to possess the mecA gene, which was discrepant with their phenotypes. Fifty-five blood culture samples were also tested by ED-PCR. For staphylococcal isolates in 33 of the cultures, oxacillin MICs were >4 microgram/ml; 31 of the 33 staphylococcal isolates were determined by ED-PCR to be mecA gene positive. These results suggest that ED-PCR can be used with reasonable confidence in the clinical microbiological laboratory.     

Correlation between genotype and phenotypic categorization of staphylococci based on methicillin susceptibility and resistance

Positive correlation between methicillin and oxacillin susceptibility test results and the detection of the mecA gene was observed for Staphylococcus aureus, S. epidermidis, and S. haemolyticus as well as among mecA(+) strains of other species of coagulase-negative staphylococci (CNS). However, at least 50% of the mecA-negative strains of these other species of CNS were falsely classified as methicillin and oxacillin resistant.     

Molecular characterization of femA from Staphylococcus hominis and Staphylococcus saprophyticus, and femA-based discrimination of staphylococcal species

The femA gene encodes a protein precursor which plays a role in peptidoglycan biosynthesis in Staphylococcus aureus and is also considered as a factor influencing the level of methicillin resistance. A femA homologous gene was recently characterized in S. epidermidis, entailing the possibility of femA phylogenetic conservation in staphylococcal species. Accordingly, we assessed the presence of femA homologous genes in S. hominis and S. saprophyticus. Strategy for identification relied upon alignment of S. aureus and D. epidermidis femA sequences and upon identification of potentially conserved regions. Amplifications of portions of the femA genes were performed under permissive annealing conditions, by using several sets of primers designed to match the consensus regions. DNA sequencing of overlapping PCR fragments led to the characterization of the entire femA genes of S. hominis and S. saprophyticus, and provided more precise information on the femA start codon for all five species. The genomic organization of all these femA genes appeared highly conserved, with alternance of homologous and variable regions. On this basis, a consensus sequence of the femA gene was defined and interspecies variations were exploited to design strategies for staphylococci species-specific identification, including multiplex PCR amplification and a reverse hybridization assay.     

Multiplex PCR for identification of methicillin-resistant staphylococci in the clinical laboratory.

A multiplex PCR assay for detection of the staphylococcal mecA gene (the structural gene for penicillin-binding protein 2a) was compared with agar dilution and disk diffusion susceptibility test methods for identifying methicillin resistance. The multiplex PCR assay combined two primer sets (mecA and 16S rRNA) in a single reaction. A total of 500 staphylococcal isolates (228 isolates of Staphylococcus aureus and 272 isolates of coagulase-negative staphylococci) from clinical specimens were studied. For S. aureus, 40 of 40 mecA-positive isolates and 4 of 188 mecA-negative isolates were oxacillin resistant (positive and negative predictive values of 100 and 98%, respectively). In 3 of 4 discordant isolates, resistance was due to hyperproduction of beta-lactamase. For coagulase-negative staphylococci, 148 of 159 mecA-positive isolates and 0 of 113 mecA-negative isolates were oxacillin resistant (positive and negative predictive values of 93 and 100%, respectively). Twenty-six isolates were categorized as indeterminate because of the absence of a detectable 16S rRNA product. Four of these 26 isolates contained mecA when retested. The assay is designed to be incorporated into the work flow of the clinical microbiology laboratory and allows for the identification of intrinsic resistance in a timely and reliable manner.     

Rapid detection of methicillin-resistant Staphylococcus aureus directly from sterile or nonsterile clinical samples by a new molecular assay

A rapid procedure was developed for detection and identification of methicillin-resistant Staphylococcus aureus (MRSA) directly from sterile sites or mixed flora samples (e.g., nose or inguinal swabs). After a rapid conditioning of samples, the method consists of two main steps: (i) immunomagnetic enrichment in S. aureus and (ii) amplification-detection profile on DNA extracts using multiplex quantitative PCR (5'-exonuclease qPCR, TaqMan). The triplex qPCR assay measures simultaneously the following targets: (i) mecA gene, conferring methicillin resistance, common to both S. aureus and Staphylococcus epidermidis; (ii) femA gene from S. aureus; and (iii) femA gene from S. epidermidis. This quantitative approach allows discrimination of the origin of the measured mecA signal. qPCR data were calibrated using two reference strains (MRSA and methicillin-resistant S. epidermidis) processed in parallel to clinical samples. This 96-well format assay allowed analysis of 30 swab samples per run and detection of the presence of MRSA with exquisite sensitivity compared to optimal culture-based techniques. The complete protocol may provide results in less than 6 h (while standard procedure needs 2 to 3 days), thus allowing prompt and cost-effective implementation of contact precautions.     

Real-time PCR can rapidly detect methicillin-susceptible and methicillin-resistant Staphylococcus aureus directly from positive blood culture bottles

We developed, validated, and implemented real-time polymerase chain reaction (PCR) detection of the femA gene for Staphylococcus aureus and the mecA gene for methicillin resistance directly from BACTEC (Becton Dickinson, Sparks, MD) blood culture bottles showing gram-positive cocci in clusters. For the 332 positive blood cultures tested, the assay had 100% sensitivity and specificity for identifying methicillin-susceptible (n=28) and methicillin-resistant (n=28) S aureus, and overall was 98% sensitive and 94% specific, with 3 uninterpretable test results when identification of coagulase-negative staphylococci was included. PCR detection yields rapid (2-3 hours) results and accurate identification of S aureus directly from signal-positive blood culture bottle samples.     

Validation of multiplex PCR strategy for simultaneous detection and identification of methicillin resistant Staphylococcus aureus

Multiplex polymerase chain reaction (PCR) strategy is described for rapid identification of clinically relevant methicillin resistant Staphylococcus aureus (MRSA) that targets mecA and coagulase genes. In this study, 150 staphylococcal clinical isolates were used that included 40 isolates of MRSA, 55 isolates of methicillin susceptible S. aureus (MSSA), 44 isolates of methicillin susceptible coagulase negative Staphylococcus spp. (MS-CoNS) and 11 isolates of methicillin resistant coagulase negative Staphylococcus spp. (MR-CoNS). Out of 55 S. aureus strains, three strains demonstrated mecA gene, which appeared to be oxacillin sensitive by disc diffusion. When (MS-CoNS) were evaluated, 10 isolates classified as oxacillin sensitive phenotypically, yielded positive results in PCR method. The results for mecA detection by PCR were more consistent with disk susceptibility tests in case of MRSA (100%) and MSSA (95%) isolates. In contrast to above results with MRSA and MSSA, mecA detection by PCR in MS-CoNS showed less correlation with disk susceptibility tests (77%). The results for coag detection by PCR were consistent with phenotypic tests in all isolates.     

Outbreak of Mupirocin-Resistant Staphylococci in a Hospital in Warsaw, Poland, Due to Plasmid Transmission and Clonal Spread of Several Strains

An outbreak of mupirocin-resistant (MuR) staphylococci was investigated in two wards of a large hospital in Warsaw, Poland. Fifty-three MuR isolates of Staphylococcus aureus, S. epidermidis, S. haemolyticus, S. xylosus, and S. capitis were identified over a 17-month survey which was carried out after introduction of the drug for the treatment of skin infections. The isolates were collected from patients with infections, environmental samples, and carriers; they constituted 19.5% of all staphylococcal isolates identified in the two wards during that time. Almost all the MuR isolates were also resistant to methicillin (methicillin-resistant S. aureus and methicillin-resistant coagulase-negative staphylococci). Seven of the outbreak isolates expressed a low-level-resistance phenotype (MuL), whereas the remaining majority of isolates were found to be highly resistant to mupirocin (MuH). The mupA gene, responsible for the MuH phenotype, has been assigned to three different polymorphic loci among the strains in the collection analyzed. The predominant polymorph, polymorph I (characterized by a mupA-containing EcoRI DNA fragment of about 16 kb), was located on a specific plasmid which was widely distributed among the entire staphylococcal population. All MuR S. aureus isolates were found to represent a single epidemic strain, which was clonally disseminated in both wards. The S. epidermidis population was much more diverse; however, at least four clusters of closely related isolates were identified, which suggested that some strains of this species were also clonally spread in the hospital environment. Six isolates of S. epidermidis were demonstrated to express the MuL and MuH resistance mechanisms simultaneously, and this is the first identification of such dual MuR phenotype-bearing strains. The outbreak was attributed to a high level and inappropriate use of mupirocin, and as a result the dermatological formulation of the drug has been removed from the hospital formulary.     

Rapid Detection of Methicillin Resistance in Staphylococcus aureus Isolates by the MRSA-Screen Latex Agglutination Test

The slide agglutination test MRSA-Screen (Denka Seiken Co., Niigata, Japan) was compared with the mecA PCR ("gold standard") for the detection of methicillin resistance in Staphylococcus aureus. The MRSA-Screen test detected the penicillin-binding protein 2a (PBP2a) antigen in 87 of 90 genetically diverse methicillin-resistant S. aureus (MRSA) stock culture strains, leading to a sensitivity of 97%. The three discrepant MRSA strains displayed positive results only after induction of the mecA gene by exposure to methicillin. Both mecA PCR and MRSA-Screen displayed negative results among the methicillin-susceptible S. aureus strains (n = 106), as well as for Micrococcus spp. (n = 10), members of the family Enterobacteriaceae (n = 10), Streptococcus pneumoniae (n = 10), and Enterococcus spp. (n = 10) (specificity = 100%). Producing the same PBP2a antigen, all 10 methicillin-resistant Staphylococcus epidermidis strains score positived in both the latex test and the mecA PCR. Consequently, the MRSA-Screen test should be applied only after identification of the MRSA strain to the species level to rule out coagulase-negative staphylococci. In conclusion, due to excellent specificity and sensitivity the MRSA-Screen latex test has the potential to be successfully used for routine applications in the microbiology laboratory.     

Correlation of oxacillin MIC with mecA gene carriage in coagulase-negative staphylococci

The National Committee for Clinical Laboratory Standards has recently changed the oxacillin breakpoint from >/=4 mg/liter to >/=0. 5 mg/liter to detect methicillin-resistant coagulase-negative staphylococci (CoNS) because the previous breakpoint lacked sensitivity. To determine the correlation between the new oxacillin breakpoint and the presence of the mecA gene, 493 CoNS of 11 species were tested. The presence of the mecA gene was determined by PCR, and oxacillin susceptibility was determined by the agar dilution method with Mueller-Hinton agar containing 2% NaCl and oxacillin (0. 125 to 4.0 mg/liter). The new breakpoint correctly classified all CoNS strains with mecA as methicillin resistant and strains of Staphylococcus epidermidis, S. haemolyticus, and S. hominis without mecA as methicillin susceptible. The breakpoint of >/=0.5 mg/liter was not specific for S. cohnii, S. lugdunensis, S. saprophyticus, S. warneri, and S. xylosus, in that it categorized 70 of 74 strains of these species without mecA (94.6%) as methicillin resistant. The results of this study indicate that the new oxacillin breakpoint accurately identifies strains of CoNS with mecA but is not specific for strains of certain species of CoNS without mecA.     

Genotype MRSA, a new genetic test for the rapid identification of staphylococci and detection of mecA gene

Early detection of Staphylococcus methicillin resistance (MR) is essential. However MR determination may be difficult because it is necessary to perform investigation of heterogeneous resistance and low level of resistance and to discriminate between oxacillin resistance and borderline resistance. Several phenotypic methods are recommended but they fail to detect low level of production de PBP2a, the modified Penicillin Binding Protein responsible for MR. Detection of mecA gene, the gene encoding PBP2a, using PCR is considered to be the reference method. We evaluated Genotype MRSA, a new rapid system based on DNA multiplex amplification and further hybridisation, for the identification of staphylococci and detection of the mecA gene. The study was performed on a collection of various Staphylococcus strains (N=30) from clinical human isolates including S. aureus MR and methicillin susceptible (MS), S. epidermidis MR and MS, and other species of coagulase negative Staphylococcus (CNS) MR and MS. For all the strains, the hybridization banding pattern obtained using Genotype MRSA correlated with their expected phenotypic and genotypic characteristics. Genotype MRSA allows the identification of the mecA gene as well as S. aureus and S. epidermidis specific genes. This DNA strip technology based assay can easily be incorporated into routine diagnostics. In addition, the short testing time (less than 2 hours) optimises treatment orientation. Genotype MRSA completely complies with all requirements for a fast, safe, valid and cost-effective MR diagnosis in staphylococci.     

Early Screening of oxacillin-resistant Staphylococcus aureus and Staphylococcus epidermidis from blood culture

The timely detection of blood-borne pathogens is one of the most important functions of the microbiology laboratory. Recently, methicillin-resistant staphylococci have become the most important pathogens seen by the laboratory. The purpose of this study was to evaluate Staphy agar, a novel screening medium, for the detection methicillin-resistant Staphylococcus aureus, S. epidermidis, or other coagulase-negative staphylococci (CNS) from positive blood cultures showing Gram-positive cocci in clusters. Eighty-six blood cultures that yielded Gram-positive cocci in clusters were included in this study. The organisms were finally identified by the Vitek system, and oxacillin resistance was confirmed by polymerase chain reaction (PCR)-based mecA gene detection. The identification and oxacillin resistance of all S. aureus strains showed complete agreement with the Vitek and PCR results. The presumptive detection of S. epidermidis and other CNS were consistent with the Vitek system in 94.7%, and the screening of oxacillin resistance was consistent with the result of PCR in 92.1% of 38 strains. The Staphy agar method is reliable and rapid for differentiating Gram-positive cocci in clusters in blood and for determining their methicillin resistance.     

Multiplex PCR protocol for the diagnosis of staphylococcal infection

We report the development of a multiplex PCR protocol for the diagnosis of staphylococcal infection. The protocol was designed to (i) detect any staphylococcal species to the exclusion of other bacterial pathogens (based on primers corresponding to Staphylococcus-specific regions of the 16S rRNA genes), (ii) distinguish between S. aureus and the coagulase-negative staphylococci (CNS) (based on amplification of the S. aureus-specific clfA gene), and (iii) provide an indication of the likelihood that the staphylococci present in the specimen are resistant to oxacillin (based on amplification of the mecA gene). The expected fragments were amplified from each of 60 staphylococcal isolates (13 oxacillin-resistant S. aureus isolates, 23 oxacillin-sensitive S. aureus isolates, 17 oxacillin-resistant CNS, and 7 oxacillin-sensitive CNS). No amplification products were observed with template DNA from nonstaphylococcal species, and the efficiency of amplification of staphylococcal targets was not adversely affected by the presence of DNA from other bacterial species in the same sample. The utility of the protocol for the analysis of clinical samples was verified by analysis of aliquots taken directly from BacT/Alert blood culture bottles. Of 77 blood cultures tested, only 7 yielded results inconsistent with those of conventional methods of diagnosis and susceptibility testing. Of those, one was identified as a CNS species by PCR and S. aureus by conventional methods. We also identified two isolates that were mecA positive but were oxacillin sensitive according to conventional methods. The other four samples failed to yield any amplification product even with a control set of primers corresponding to a conserved region of the eubacterial rRNA genes.     

Sequential analysis of staphylococcal colonization of body surfaces of patients undergoing vascular surgery.

Slime-producing coagulase-negative staphylococci are pathogens in vascular surgery by virtue of their ability to adhere to and persist on prosthetic graft material. Inguinal and abdominal skin sites were cultured in 41 patients upon hospitalization, and slime production and antimicrobial susceptibility were assessed in all recovered staphylococcal isolates. Twenty-one patients eventually underwent lower-extremity revascularization. In the operative population, cultures were also obtained on the day of surgery and fifth postoperative day. All 21 patients received perioperative cefazolin. Of 327 coagulase-negative staphylococci recovered, Staphylococcus epidermidis (47%), S. haemolyticus (21%), and S. hominis (10%) were the predominant isolates. Slime-producing coagulase-negative staphylococci were recovered from 17 of 21 patients at admission but only from 8 of 21 patients on day 5 postoperation (P less than 0.05). S. epidermidis isolates demonstrated increasing multiple resistance from admission to 5 days postoperation to methicillin, gentamicin, clindamycin, erythromycin, and trimethoprim-sulfamethoxazole (P less than 0.05). All coagulase-negative staphylococcal isolates were susceptible to ciprofloxacin and vancomycin. Slime-producing capability was not associated with increased methicillin resistance for the recovered isolates. The data demonstrate that patients enter the hospital colonized with slime-producing strains of coagulase-negative staphylococci and that during hospitalization the staphylococcal skin burden shifts from a predominately susceptible to a resistant microbial population, which may enhance the importance of slime production as a risk factor in lower-extremity revascularization.     

Multiplex PCR for detection of genes for Staphylococcus aureus enterotoxins, exfoliative toxins, toxic shock syndrome toxin 1, and methicillin resistance

A multiplex PCR assay for detection of genes for staphylococcal enterotoxins A to E (entA, entB, entC, entD, and entE), toxic shock syndrome toxin 1 (tst), exfoliative toxins A and B (etaA and etaB), and intrinsic methicillin resistance (mecA) was developed. Detection of femA was used as an internal positive control. The multiplex PCR assay combined the primers for sea to see and femA in one set and those for eta, etb, tst, mecA, and femA in the other set. Validation of the assay was performed using 176 human isolates of Staphylococcus aureus. This assay offers a very specific, quick, reliable, and inexpensive alternative to conventional PCR assays used in clinical laboratories to identify various staphylococcal toxin genes.     

Detection of the Staphylococcal mecA gene by chemiluminescent DNA hybridization.

A new solution-phase DNA hybridization capture assay for the rapid detection of the mecA gene in clinical isolates of Staphylococcus was compared with multiplex PCR and disk diffusion methods. The assay uses a DNA capture probe immobilized on paramagnetic particles and a second DNA probe labeled with an acridinium ester. Bacteria from 24-h cultures are lysed, and the lysates are hybridized with the DNA probes. After magnetic separation to remove unhybridized labeled probe, the mecA gene is detected by the chemiluminescence of the hybridized probe. Four hundred consecutive staphylococcal isolates were assayed, including 147 S. aureus and 253 coagulase-negative Staphylococcus isolates. Among the S. aureus isolates, 14 of 147 were MecA+ by both the hybridization capture assay and PCR; 133 of 147 were MecA negative by both assays (positive and negative predictive values, 100%). Comparison of disk diffusion results with those obtained by genotypic methods indicated that 14 of 147 S. aureus isolates judged to be resistant were positive by both methods; 119 of 147 were Oxs and negative by both genotypic methods (positive and negative predictive values, 50 and 100%, respectively). The remaining 14 S. aureus isolates were MecA- Oxr; among these, 13 were beta-lactamase hyperproducers. For coagulase-negative staphylococci, 130 of 253 were MecA+ by the hybridization capture assay; 129 of 130 of these isolates were positive by PCR (positive and negative predictive values, 99.2 and 100%, respectively). Comparison with the disk diffusion assay showed that 128 of the coagulase-negative MecA+ isolates were Oxr; 111 of 253 were MecA- and Oxs (positive and negative predictive values, 90.8 and 99.1%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Slime Production and Expression of the Slime-Associated Antigen by Staphylococcal Clinical Isolates

The ability to produce slime and to express a slime-associated antigen was examined in a collection of staphylococcal clinical isolates. Slime-producing strains were found among coagulase-negative staphylococci in percentages comparable to those reported in other studies; surprisingly, a high percentage of Staphylococcus aureus strains also were able to produce this extracellular material. In the latter case, this ability was strongly dependent on the presence of an additional carbohydrate source in the growth medium. Expression of the slime-associated antigen appeared to be species specific and confined to the Staphylococcus epidermidis sensu stricto isolates; its strong association with the ability of these strains to produce thicker biofilms indicated slime-associated antigen as a possible virulence marker for S. epidermidis.