High diversity of Panton–Valentine leukocidin-positive, methicillin-susceptible isolates of Staphylococcus aureus and implications for the evolution of community-associated methicillin-resistant S. aureus

In total, 100 Staphylococcus aureus isolates from diverse cases of skin and soft-tissue infection at a university hospital in Saxony, Germany, were characterised using diagnostic microarrays. Virulence factors, including Panton-Valentine leukocidin (PVL), were detected and the isolates were assigned to clonal groups. Thirty isolates were positive for the genes encoding PVL. Only three PVL-positive methicillin-resistant S. aureus (MRSA) isolates were found, two of which belonged to European clone ST80-MRSA IV and one to USA300 strain ST8-MRSA IV. The remaining methicillin-susceptible PVL-positive isolates belonged to a variety of different multilocus sequence types. The predominant strains were agrI/ST22, agrII/CC5, agrIII/CC30 and agrIV/ST121. In order to check for possible bias caused by regional or local outbreak strains, an additional 18 methicillin-susceptible, PVL-positive isolates from the UK were tested. Approximately two-thirds of the UK isolates belonged to types that also comprised approximately two-thirds of the isolates from Saxony. Some methicillin-susceptible PVL-positive isolates (agrI/ST152, agrIII/ST80 and agrIII/ST96) closely resembled known epidemic community-acquired MRSA (CaMRSA) strains. These findings indicate that the current rise in PVL-positive CaMRSA could be caused by the dissemination of novel SCCmec elements among pre-existing PVL-positive strains, rather than by the spread of PVL phages among MRSA strains.     

Increasing incidence and widespread dissemination of methicillin-resistant Staphylococcus aureus (MRSA) in hospitals in central Europe, with special reference to German hospitals

Objective: to present data on prevalence and interregional spread of methicillin-resistant Staphylococcus aureus (MRSA) in Germany.
Methods: A nationwide collection of MRSA isolates from nosocomial infections in 143 hospitals was established from isolates ( n =4368) sent to a microbiological reference center during 1993–95. As chosen by distinguishable resistance phenotypes at each time of occurrence during the study period, 1830 isolates were subjected to molecular typing by means of Sma l macrorestriction patterns, PCR for RNA gene spacer patterns, and PCR for patterns of DNA stretches flanked by the ERIC-2 sequence and flanked by Tn 976 and ribosomal binding site. In addition, data from a multicenter study on the incidence of antibiotic resistance have been analyzed (32 centers, 637 S. aureus isolates).
Results: In 1995 the prevalence of MRSA among S. aureus isolates was 8.7% overall in central Europe (including Germany), in comparison to 1.7% in 1990. From 1993 until now, a continuous interregional dissemination of six epidemic strains, which were identified by molecular typing, was recorded. Besides these epidemic strains, 15 MRSA strains were identified which could not be allocated to the epidemic MRSA or to the known clonal groups of the species S. aureus. MRSA from three cases of sporadic nosocomial infections exhibited characteristics of the clonal group of S. aureus with the capacity for toxic shock syndrome formation. The pattern of one MRSA corresponded to those of the S. aureus group exhibiting phage pattern 94,96.
Conclusions: The prevalence of MRSA has increased in central Europe (and Germany) during the last 5 years, to 8.7%. The main source of infection with MRSA is obviously interregional dissemination of epidemic strains. At the same time, the mecA gene has been acquired by strains previously sensitive to methicillin.     

The molecular evolution of methicillin-resistant Staphylococcus aureus

Staphylococcus aureus is a potentially pathogenic bacterium that causes a broad spectrum of diseases. S. aureus can adapt rapidly to the selective pressure of antibiotics, and this has resulted in the emergence and spread of methicillin-resistant S. aureus (MRSA). Resistance to methicillin and other β-lactam antibiotics is caused by the mecA gene, which is situated on a mobile genetic element, the Staphylococcal Cassette Chromosome mec (SCC mec ). To date, five SCC mec types (I–V) have been distinguished, and several variants of these SCC mec types have been described. All SCC mec elements carry genes for resistance to β-lactam antibiotics, as well as genes for the regulation of expression of mecA . Additionally, SCC mec types II and III carry non-β-lactam antibiotic resistance genes on integrated plasmids and a transposon. The epidemiology of MRSA has been investigated by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), spa typing and SCC mec typing. Numerous MRSA clones have emerged and disseminated worldwide. SCC mec has been acquired on at least 20 occasions by different lineages of methicillin-sensitive S. aureus . Although most MRSA strains are hospital-acquired (HA-MRSA), community-acquired MRSA (CA-MRSA) strains have now been recognised. CA-MRSA is both phenotypically and genotypically different from HA-MRSA. CA-MRSA harbours SCC mec types IV or V, and is associated with the genes encoding Panton–Valentine leukocidin. The prevalence of MRSA ranges from 0.6% in The Netherlands to 66.8% in Japan. This review describes the latest developments in knowledge concerning the structure of SCC mec , the molecular evolution of MRSA, the methods used to investigate the epidemiology of MRSA, and the risk-factors associated with CA-MRSA and HA-MRSA.     

Evaluation of two new chromogenic media, CHROMagar MRSA and S. aureus ID, for identifying Staphylococcus aureus and screening methicillin-resistant S. aureus

Thirty-nine methicillin-resistant Staphylococcus aureus (MRSA) isolates with diverse genetic backgrounds and two reference strains were correctly identified as S. aureus on CHROMagar MRSA and S. aureus ID media. Growth inhibition on CHROMagar MRSA was noted. A combination of cefoxitin disk and S. aureus ID was found suitable for rapid MRSA screening.     

Comparison of culture screening protocols for methicillin-resistant Staphylococcus aureus (MRSA) using a chromogenic agar (MRSA-Select)

To compare the culture screening protocols for methicillin-resistant Staphylococcus aureus (MRSA), a total of 300 duplicate nasal swabs (233 initial cultures and 67 weekly follow-up cultures) were collected consecutively from 233 patients in the Intensive Care Unit (ICU). One swab was plated directly on MRSA-Select agar (D-MRSA-Select) and observed at 24 hr. The duplicate swab was incubated in tryptic soy broth (TSB) with 6.5% NaCl for 24 hr, and then subcultured on MRSA-Select (B-MRSA-Select), BAP (B-BAP), and mannitol salt agar with 4 mg/L oxacillin (B-MSA(OXA)), and observed at 24 hr. MRSA was detected in 13.7% (32/233) of the initial and 22.4% (15/67) of the follow-up specimens. A patient was classified as MRSA-positive if any of the media grew colonies that were tested and confirmed to be MRSA. In the initial screening samples, the sensitivities of D-MRSA-Select, B-MRSA-Select, B-BAP, and B-MSA(OXA) were 78.1%, 84.4%, 78.1%, and 65.6%, respectively, and the specificities were 100%, 98.0%, 83.1%, and 93.5%, respectively. The sensitivities of all but the B-MRSA-Select protocol were significantly lower (p <0.05). In follow-up screening, the sensitivities of D-MRSA-Select, B-MRSA-Select, B-BAP, and B-MSA(OXA) were 66.7%, 86.7%, 66.7%, and 53.3%, respectively, and the specificities were 100%, 98.1%, 90.4%, and 90.4%, respectively. D-MRSA-Select protocol was considered useful in screening for MRSA because it was fast, highly specific, and showed sensitivity comparable to B-BAP. Salt-containing enrichment broth in conjunction with MRSA-Select (B-MRSA-Select) provides a promising way to increase sensitivity in initial and follow-up screening for MRSA.     

Predictors of clinical and microbiological treatment failure in patients with methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia: a retrospective cohort study in a region with low MRSA prevalence

Invasive infections with methicillin-resistant Staphylococcus aureus (MRSA) have been associated with increased morbidity and mortality. The aim of the present study was to identify independent predictors of early mortality and treatment failure in patients with MRSA bacteraemia. A total of 132 adult patients who developed MRSA bacteraemia during hospitalization in the University Hospital of Vienna between 2000 and 2011 were screened and 124 were included in a retrospective cohort study. Patient demographics, source of bacteraemia, antimicrobial treatment and microbiological characteristics were evaluated. The 28-day crude mortality was 30.6%. Predictors of early mortality identified in multivariate Cox regression analysis included higher patientage (adjusted hazard ratio (aHR) 1.03, 95% CI 1.01–1.06, p 0.006), pneumonia (aHR 3.86, 95% CI 1.83–8.12, p <0.001) and failure to use MRSA active treatment (aHR 8.77, 95% CI 3.50–21.93, p <0.001). Ninety-one (73.4%) patients received glycopeptides as specific MRSA treatment. Of 63 patients treated with vancomycin, only 14 (22.6%) patients had aimed trough levels of 15–20 mg/L. Vancomycin MIC ≥ 2 mg/L was detected in 28.2% and was associated with glycopeptide pretreatment (p 0.001). All MRSA isolates were susceptible to linezolid and tigecycline. Persistent bacteraemia ≥ 7 days was documented in 25 (20.2%) patients. Independent determinants for microbiological eradication failure in patients with MRSA bacteraemia included endocarditis (p <0.001) and vancomycin trough levels (p 0.014), but not vancomycin MIC. Failure of clinical and microbiological eradication of MRSA among patients with MRSA bacteraemia was associated with clinical entity rather than with bacterial traits. Pharmacokinetic parameters seem to be decisive on microbiological and clinical success.     

Activity of medicinal plant extracts against hospital isolates of methicillin-resistant Staphylococcus aureus

Aqueous and ethanolic extracts of ten traditional Thai medicinal plants were investigated for their ability to inhibit 35 hospital isolates of methicillin-resistant Staphylococcus aureus (MRSA). Nine medicinal plants displayed activity against all isolates tested. Ethanolic extracts of Garcinia mangostana, Punica granatum and Quercus infectoria were most effective, with MICs for MRSA isolates of 0.05-0.4, 0.2-0.4 and 0.2-0.4 mg/mL, respectively, and for S. aureus ATCC 25923 of 0.1, 0.2 and 0.1 mg/mL, respectively. MBCs for MRSA isolates were 0.1-0.4, 1.6-3.2 and 0.4-1.6 mg/mL, and for S. aureus ATCC 25923 were 0.4, 3.2 and 1.6 mg/mL, respectively.     

Prevalence of methicillin-resistant Staphylococcus aureus among veterinarians: an international study.

Pig farmers and veterinarians in contact with livestock in The Netherlands have a higher risk of methicillin-resistant Staphylococcus aureus (MRSA) carriage than the general population. The objective of this study was to investigate whether this is also true for other professionals in contact with pigs in an international setting. A convenience sample of 272 participants at an international conference on pig health in Denmark was screened for MRSA carriage using combined nose/throat swabs and were asked to complete a questionnaire concerning animal contacts, exposure to known MRSA risk-factors, and the protective measures taken when entering pig farms. In total, 34 (12.5%) participants from nine countries carried MRSA. Thirty-one of these isolates were non-typeable by pulsed-field gel electrophoresis following SmaI digestion of chromosomal DNA. All of the non-typeable isolates belonged to spa types (t011, t034, t108, t571, t567 and t899) that correspond to multilocus sequence type 398. All of the above-mentioned spa types, with the exception of t899, have been isolated previously from either Dutch pigs, pig farmers and/or veterinarians. Protective measures, e.g., masks, gowns and gloves, did not protect against MRSA acquisition. Transmission of MRSA from pigs to staff tending to these animals appears to be an international problem, creating a new reservoir for community-acquired MRSA (CA-MRSA) in humans in Europe, and possibly worldwide. The rise of a new zoonotic source of MRSA could have a severe impact on the epidemiology of CA-MRSA, and may have consequences for the control of MRSA, especially in those countries that maintain a low prevalence by means of search-and-destroy policies.     

Effectiveness of a hospital-wide selective screening programme for methicillin-resistant Staphylococcus aureus (MRSA) carriers at hospital admission to prevent hospital-acquired MRSA infections

Screening of potential MRSA-positive patients at hospital admission is recommended in German and international guidelines. This policy has been shown to be effective in reducing the frequency of nosocomial MRSA transmissions in the event of an outbreak, but the influence of screening on reducing hospital-acquired MRSA infections in a hospital setting where MRSA is endemic is not yet well-documented. This study describes the effect of hospital-wide screening of defined risk groups in a 700-bed acute care hospital during a period of 19 months. In a cohort study with a 19-month control period, the frequencies of hospital-acquired MRSA infections were compared with and without screening. In the control period, there were 119 MRSA-positive patients, of whom 48 had a hospital-acquired MRSA infection. On the basis of this frequency, a predicted total of 73.2 hospital-acquired MRSA infections was calculated for the screening period, but only 52% of the expected number (38 hospital-acquired MRSA infections) were observed, i.e., 48% of the predicted number of hospital-acquired MRSA infections were prevented by the screening programme. The screening programme was performed with minimal effort and can therefore be recommended as an effective measure to help prevent hospital-acquired MRSA infections.     

Reduction in the rate of methicillin-resistant Staphylococcus aureus acquisition in surgical wards by rapid screening for colonization: a prospective,cross-over study

Identification of patients colonized with methicillin-resistant Staphylococcus aureus (MRSA) and subsequent isolation and decolonization is pivotal to the control of cross infection in hospitals. The aim of this study was to establish if early identification of colonized patients using rapid methods alone reduces transmission. A prospective, cluster, two-period cross-over design was used. Seven surgical wards at a large hospital were allocated to two groups, and for the first 8 months four wards used rapid MRSA screening and three wards used a standard culture method. The groups were reversed for the second 8 months. Regardless of the method of detection, all patients were screened for nasal carriage on admission and then every 4 days. MRSA control measures remained constant. Results were analysed using a log linear Poisson regression model. A total of 12 682/13 952 patient ward episodes (PWE) were included in the study. Admission screening identified 453 (3.6%) MRSA-positive patient ward episodes, with a further 268 (2.2%) acquiring MRSA. After adjusting for other variables, rapid screening was shown to statistically reduce MRSA acquisition, with patients being 1.49 times (p 0.007) more likely to acquire MRSA in wards where they were screened using the culture method. Screening of surgical patients using rapid testing resulted in a statistically significant reduction in MRSA acquisition. This result was achieved in a routine surgical service with high bed occupancy and low availability of isolation rooms, making it applicable to the majority of health-care systems worldwide.     

Real-time multiplex PCR for direct detection of methicillin-resistant Staphylococcus aureus (MRSA) in clinical samples enriched by broth culture

A real-time multiplex PCR using the orfX and staphylococcal cassette chromosome (SCC) mec of Staphylococcus aureus was developed. The aim was to achieve a rapid and sensitive high-throughput method for direct detection of heterogeneous methicillin-resistant S. aureus (MRSA) in clinical samples, present in a low-endemic population, such as in Sweden. Consecutive broth enriched pooled clinical screening samples (nares, throat and/or perineum/groin) (n = 541 pools), broth enriched clinical samples showing growth of methicillin-sensitive S. aureus (MSSA) (n = 95 pools), clinical MRSA isolates (n = 173), MRSA reference strains (n = 43) and various coagulase-negative staphylococcal isolates (n = 33) were analyzed. The multiplex PCR detected all heterogeneous MRSA strains (n = 173) obtained in our area as well as all pooled consecutive broth enriched clinical samples with MRSA, i. e. 36 of 541 pools. None of the CoNS were positive. However, 18 out of 541 pools (3.3%) were positive in the multiplex PCR but no growth of MRSA could be detected by subculture and were regarded as false positive. Furthermore, the assay is rapid and reliable negative results can be delivered to the clinician within 18 h that will facilitate the infection control management of patients and hospital staff.     

Characterisation of methicillin-resistant Staphylococcus aureus isolates from dogs and their owners

Ten methicillin-resistant Staphylococcus aureus (MRSA) isolates from healthy owners and their pets were characterised by susceptibility testing, staphylococcal chromosome cassette (SCC)mec and agr typing, and detection of the Panton-Valentine leukocidin (PVL) genes. Two human and three dog isolates harbouring SCCmec type III appeared to be of hospital origin. The five remaining isolates carried SCCmec type IV, with three being multidrug-resistant. One type IV isolate was PVL-positive and a prototypic agr type 3, typified by strain MW2. This is the first report of this type in association with nasal carriage. Drug resistance may be increasing among community isolates of MRSA.     

Rapid genotyping of methicillin-resistant Staphylococcus aureus (MRSA) isolates using miniaturised oligonucleotide arrays

This study evaluated a DNA oligonucleotide array that recognised 38 different Staphylococcus aureus targets, including all relevant resistance determinants and some toxins and species-specific controls. A new method for labelling sample DNA, based on a linear multiplex amplification that incorporated biotin-labelled dUTP into the amplicon, was established, and allowed detection of hybridisation of the amplicons to the array with an enzymic precipitation reaction. The whole assay was validated by hybridisations with a panel of reference strains and cloned specific PCR products of all targets. To evaluate performance under routine conditions, the assay was used to test 100 methicillin-resistant S. aureus (MRSA) isolates collected from a university hospital in Saxony, Germany. The results showed a high correlation with conventional susceptibility data. The ermA and ermC macrolide resistance genes were found in 40% and 32% of the isolates, respectively. The most prevalent aminoglycoside resistance gene was aphA3 (57% of the isolates), followed by aacA-aphD (29%) and aadD (29%); tet genes, mupR and dfrA were rare. There were no isolates with van genes or genes involved in resistance to quinupristin-dalfopristin. Enterotoxins were detected in 27% of the isolates. Genes encoding Panton-Valentine leukocidin, toxic shock syndrome toxin and exfoliative toxins were not found. The DNA array facilitated rapid and reliable detection of resistance determinants and toxins under conditions used in a routine laboratory and has the potential to be used for array-based high-throughput screening.     

Nasal carriage of Staphylococcus aureus, including community-associated methicillin-resistant strains, in Queensland adults

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections are emerging in southeast Queensland, Australia, but the incidence of carriage of CA-MRSA strains is unknown. The aim of this study was to assess the nasal carriage rate of S. aureus , including CA-MRSA strains, in the general adult population of southeast Queensland. 396 patients presenting to general practices in two Brisbane suburbs and 303 volunteers randomly selected from the electoral rolls in the same suburbs completed a medical questionnaire and had nasal swabs performed for S. aureus . All isolates of S. aureus underwent antibiotic susceptibility testing and single-nucleotide polymorphism (SNP) and binary typing, including determination of Panton–Valentine leukocidin (PVL). The nasal carriage rate of methicillin-susceptible S. aureus (MSSA) was 202/699 (28%), a rate similar to that found in other community-based nasal carriage studies. According to multivariate analysis, nasal carriage of S. aureus was associated with male sex, young adult age group and Caucasian ethnicity. Only two study isolates (one MSSA and one CA-MRSA) carried PVL. The nasal carriage rate of MRSA was low, at 5/699 (0.7%), and only two study participants (0.3%) had CA-MRSA strains. CA-MRSA is an emerging cause of infection in southeast Queensland, but as yet the incidence of carriage of CA-MRSA in the general community is low.     

婴幼儿耐甲氧西林金黄色葡萄球菌感染状况和耐药基因的研究

目的了解感染婴幼儿的耐甲氧西林金黄色葡萄球菌（MRSA）耐药性和耐药基因,明确检测青霉素结合蛋白2a（PBP2a）和甲氧西林耐药基因（mecA）的临床价值。方法用金黄色葡萄球菌乳胶凝集试验和梅里埃鉴定金黄色葡萄球菌,同时用纸片扩散法完成12种常用抗生素的药敏试验。对头孢西丁的结果,按当年CLSI标准执行,用于判断菌株甲氧西林的耐药性。采用PBP2检测试剂盒检测PBP2a蛋白,PCR检测mecA基因。结果 2007-2009年婴幼儿共检出245株金黄色葡萄球菌,其中MRSA检出率为17.6%（43/245）。MRSA对庆大霉素、复方新诺明、克林霉素、红霉素、氯霉素的耐药性均显著高于甲氧西林敏感金黄色葡萄球菌（P〈0.05）,其余抗生素的差异无统计学意义（P〉0.05）,43株MRSA的PBP2a蛋白和mecA基因的检测结果全为阳性,阳性率为100%。结论用头孢西丁（30μg）能有效地筛查MRSA,检测PBP2a蛋白和mecA基因均能正确地确认MRSA。且检测PBP2a蛋白方便快捷,特异性好,值得临床推广。     

Molecular epidemiology of methicillin-resistant Staphylococcus aureus in Spain: a multicentre prevalence study (2002)

A point-prevalence study, performed in 2002 in 143 Spanish hospitals, collected 439 isolates of Staphylococcus aureus. Of these, 134 (30.5%) were resistant to methicillin (i.e., MRSA). Susceptibility testing was performed by a microdilution method, and mecA was detected by PCR. The isolates were characterised by phage typing, pulsed-field gel electrophoresis (PFGE) after SmaI digestion, and SCCmec typing. The 134 MRSA isolates showed resistance to ciprofloxacin (93.3%), tobramycin (88.8%), erythromycin (67.9%), clindamycin (59.7%), gentamicin (42.5%), mupirocin (17.9%), rifampicin (5.2%) and trimethoprim-sulphamethoxazole (5.2%). All of the isolates were susceptible to glycopeptides. Twenty-five resistance patterns were found, of which four accounted for 66% of the isolates. Phage group III was the most frequent (41.1%). PFGE revealed 31 different patterns, with ten major clones (including two predominant clones with variable antibiotypes that accounted for 43.3% of the MRSA isolates) and 21 sporadic patterns. Two isolates belonged to two variants of the Iberian clone (ST247-MRSA-I), one to the Brazilian clone (ST239-MRSA-III), and seven to the EMRSA-16 clone (ST36-MRSA-II). SCCmecIV accounted for 70.2% of the isolates (73.9% were type IVA), while SCCmecI, SCCmecII and SCCmecIII accounted for 22.1%, 6.9% and 0.8% of isolates, respectively, with three non-typeable isolates. Isolates of SCCmecIV and SCCmecIVA were predominantly nosocomial (95.8% and 97.1%, respectively). None of the isolates produced Panton-Valentine leukocidin. Thus, two clones carrying SCCmecIV and SCCmecIVA, respectively, were predominant among nosocomial MRSA isolates throughout Spain.     

Use of BBL CHROMagar MRSA medium for identification of methicillin-resistant Staphylococcus aureus directly from blood cultures

We evaluated the ability of BBL CHROMagar MRSA medium (Becton Dickinson, Sparks, MD) to identify methicillin-resistant Staphylococcus aureus (MRSA) directly upon subculture from positive blood culture bottles. There were 124 MRSA isolates recovered from blood cultures in the study. BBL CHROMagar MRSA medium was highly sensitive (97.6% [121/124] at 18 to 24 h of incubation and 100% [124/124] at 48 h) and 99.9% specific for identifying MRSA from positive blood cultures.     

Predominance of staphylococcal cassette chromosome mec (SCCmec) type IV among methicillin-resistant Staphylococcus aureus (MRSA) in a Swedish county and presence of unknown SCCmec types with Panton-Valentine leukocidin genes

Methicillin-resistant Staphylococcus aureus (MRSA) is an established nosocomial pathogen, but has recently begun to appear in the community. The clones in the community may not have originated in the hospital setting, and are referred to as community-acquired MRSA (CA-MRSA). Resistance to methicillin is mediated by the gene mecA, which is carried by the mobile genetic element staphylococcal cassette chromosome mec (SCCmec). SCCmec typing (I-IV) of all clinical isolates of MRSA (n = 92) from 1987 to 2004 in Orebro County, Sweden, was performed by real-time LightCycler PCR to detect the essential genetic components mecA, mecR1, IS1272, ccrA and ccrB. Forty-one isolates harboured type IV SCCmec, of which ten could be classified further as subtype IVa, and 27 as subtype IVc. No isolates belonged to subtype IVb, but four isolates could not be subtyped, and may be examples of novel type IV SCCmec subtypes. Thirty-five MRSA isolates, assigned to six different pulsotypes by pulsed-field gel electrophoresis, did not belong to SCCmec types I-IV. The Panton-Valentine leukocidin (PVL) genes were identified in two of these pulsotypes. Only SCCmec type IV has been associated previously with the PVL toxin, but the results suggest that new PVL-positive clones with novel SCCmec types may be arising and disseminating in the community.     

Multicenter evaluation of BBL CHROMagar MRSA medium for direct detection of methicillin-resistant Staphylococcus aureus from surveillance cultures of the anterior nares

Active surveillance for methicillin-resistant Staphylococcus aureus (MRSA) is among the strategies recommended by the Society for Healthcare Epidemiology of America for control of nosocomial MRSA infections. Infection control and laboratory personnel desire rapid, sensitive, and inexpensive methods to enhance surveillance activities. A multicenter study was performed to evaluate a new selective and differential chromogenic medium, BBL CHROMagar MRSA (C-MRSA) medium (BD Diagnostics, Sparks, MD), which enables recovery and concomitant identification of MRSA strains directly from nasal swab specimens taken from the anterior nares. Specimens were inoculated to C-MRSA and Trypticase soy agar with 5% sheep blood agar (TSA II, BD Diagnostics). Mauve colonies on C-MRSA at 24 h and 48 h and suspicious colonies on TSA II were confirmed as Staphylococcus aureus by Gram stain morphology and a coagulase test. In addition, the results of C-MRSA were compared to results of susceptibility testing (five different methods) of S. aureus strains isolated on TSA II. A total of 2,015 specimens were inoculated to C-MRSA and TSA II. Three hundred fifty-four S. aureus isolates were recovered; 208 (59%) were oxacillin (methicillin) susceptible and 146 (41%) were oxacillin resistant (MRSA). On C-MRSA, 139/146 or 95.2% of MRSA isolates were recovered, whereas recovery on TSA II was 86.9% (127/146) (P = 0.0027). The overall specificity of C-MRSA was 99.7%. When C-MRSA was compared to each susceptibility testing method, the sensitivity and specificity, respectively, were as follows: oxacillin MIC by broth microdilution, 94.4% and 96.7%; oxacillin screen agar, 94.3% and 96.7%; PBP2' latex agglutination, 93.7% and 98.5%; cefoxitin disk diffusion, 95.0% and 98.1%; and mecA PCR, 95.1% and 98.1%. In this study, C-MRSA was superior to TSA II for recovery of MRSA from surveillance specimens obtained from the anterior nares and was comparable to conventional, rapid, and molecular susceptibility methods for the identification of MRSA isolates.