GeneOhm Methicillin-resistant Staphylococcus Aureus Assay Research Articles

Isolation of Methicillin-resistant Staphylococcus aureus (MRSA) using a flocked swab elution transport system; with identification by PCR

Admission screening is an essential part of the control of methicillin-resistant Staphylococcus aureus (MRSA). Using collection systems that maintain viability and have high organism recovery, combined with accurate and rapid laboratory testing is critical for the success of a screening program. This review evaluates the performance of PCR testing, particularly the Roche LightCycler MRSA test, in the detection of MRSA. In addition, the clinical performance of the Copan Elution swab (ESwab) is reviewed. Several commercial molecular tests developed for use in detecting MRSA colonisation have been evaluated against culture methods, and all appear to provide high sensitivity, good specificity, and the potential for rapid reporting of MRSA colonisation. The new LightCycler MRSA advanced test is another of these assays with rapid detection time and high sensitivity. Compared with the BD GeneOhm MRSA assay, this new test also appears to have improved test specificity. The ESwab has an equal or even better recovery of bacteria, including MRSA, compared with other swab systems, via culture, and PCR. The advantages of using the ESwab are: the use of a liquid Amies medium allowed multiple uses (both culture, and PCR can be performed with one collected sample); and, specimens from multiple sites can be pooled into the same liquid transport media which limits the test costs and broadens the screening capabilities. However, there are limited publications on the clinical performance of the ESwab and more research is required on this new swab transport system.

Admission Screening of Methicillin-Resistant Staphylococcus aureus with Rapid Molecular Detection in Intensive Care Unit: A Three-Year Single-Centre Experience in Hong Kong

Background. The admission screening of methicillin-resistant Staphylococcus aureus (MRSA) by rapid molecular assay is considered to be an effective method in reducing the transmission of MRSA in intensive care unit (ICU). Method. The admission screening on patients from ICU once on their admissions by BD GeneOhm MRSA assay has been introduced to Prince of Wales Hospital, Hong Kong, since 2008. The assay was performed on weekdays and reported on the day of testing. Patients pending for results were under standard precautions until the negative screening results were notified, while contact precautions were implemented for MRSA-positive patients. In this study, we compared the MRSA transmission rate in molecular screening periods (2008 to 2010) with the historical culture periods (2006 to 2007) as control. Results. A total of 4679 samples were tested; the average carriage rate of MRSA on admission was 4.45%. By comparing with the historical culture periods, the mean incidence ICU-acquired MRSA infection was reduced from 3.67 to 1.73 per 1000 patient bed days. Conclusion. The implementation of admission screening of MRSA with molecular method in intensive care unit could reduce the MRSA transmission, especially in the area with high MRSA prevalence situation in Hong Kong.

Analysis of Staphylococcal Cassette Chromosome mec in BD GeneOhm MRSA Assay-Negative Strains

The BD GeneOhm MRSA assay could identify methicillin-resistant Staphylococcus aureus (MRSA) strains at a high ratio (97.8%). Analysis of 11 assay-negative MRSA strains suggested that insertion of non-mec staphylococcal cassette chromosome elements (SCCs) downstream of orfX, and carriage of SCCmecs with a left extremity that cannot be detected by the kit, might lead to their being given an incorrect negative status.

The Screening of Methicillin-Resistant Staphylococcus aureus in Vascular Surgery Patients: A Comparison of Molecular Testing and Broth-Enriched Culture

Background: Methicillin-resistant Staphylococcus aureus (MRSA) is a major global health care-associated pathogen. This study sought to examine the prevalence of MRSA in patients who were admitted to a vascular surgery ward during a 3-month period. Methods: MRSA screening was accomplished through the acquisition of nasal, throat and perineal swabs. These swabs were placed in tryptic soy broth that had been supplemented with 6.5% NaCl and incubated for 24 h. The resulting isolates were subcultured on agar plates containing 5% sheep blood. The BD GeneOhm MRSA assay for screening swabs was performed in accordance with the manufacturer’s instructions. Results: A total of 58 patients were included in the study and swabs from 232 sites were obtained during the sampling period. MRSA was detected in 33 samples of 12 patients during the study period; thus, there was a 20.6% prevalence of patients who were recognized as MRSA carriers. There were discrepancies between the results of classical bacteriological screening and molecular MRSA detection methods in 8 of the patients. Conclusions: Nasal, throat and perineal MRSA screening can detect the carriage of this pathogen and allow for the timely use of appropriate infection control measures. The choice of screening techniques poses a challenge; it has been demonstrated that molecular detection methods should be performed with great sensitivity, specificity and, most importantly, speed. The cost of the PCR screening method is the only disadvantage of this approach.

Genotypic and Phenotypic Characterization of Methicillin-Susceptible Staphylococcus aureus Isolates Misidentified as Methicillin-Resistant Staphylococcus aureus by the BD GeneOhm MRSA Assay

Twenty-three nasal swab samples that tested positive for methicillin-resistant Staphylococcus aureus (MRSA) on initial testing by the BD GeneOhm MRSA assay (BD-MRSA PCR; BD GeneOhm, San Diego, CA) were culture positive only for methicillin-susceptible S. aureus (MSSA) from an enrichment broth. The 23 recovered isolates were confirmed as MSSA by a variety of phenotypic methods, including the BD Phoenix automated microbiology system (BD Diagnostics, Sparks, MD), oxacillin screening agar (BD Diagnostics), BBL CHROMagar MRSA (BD Diagnostics), and a PBP2' assay (Denka Seiken Co., Tokyo, Japan); susceptibilities were determined by using Mueller-Hinton agar with oxacillin. All were positive by nuc PCR, specific for S. aureus, but negative for mecA with one exception. Isolates were characterized by using multiplex PCR methodology to determine structural types and variants (SCCmec typing); additional PCRs were performed for the detection of the ccr and mec complexes, the junkyard regions as well as the Panton-Valentine leukocidin. Pulsed-field gel electrophoresis was used to determine clonality. One phenotypic MSSA isolate contained an intact SCCmec. Twelve MSSA isolates tested positive for MRSA by the BD-MRSA PCR because of amplification of the mec priming site flanking the SCC insertion point, although these isolates lacked mecA. The 10 remaining isolates were not MRSA and tested as MSSA by phenotypic and genotypic assays. In our patient population, diagnostic and surveillance testing and subsequent infection control practices may be impacted by the frequency of these excision events when using the BD-MRSA PCR for MRSA detection.

Evaluation of the BD GeneOhm Assay Using the Rotor-Gene 6000 Platform for Rapid Detection of Methicillin-Resistant Staphylococcus aureus from Pooled Screening Swabs

As health services move toward universal methicillin-resistant Staphylococcus aureus (MRSA) screening for hospital admissions, the most cost-effective approach is yet to be defined. In this study, one of the largest to date, we evaluated the performance of the BD GeneOhm MRSA assay on the Rotor-Gene 6000 thermal cycler, using samples taken directly from pooled MRSA screens. Results were compared with the same assay performed on the Smart-Cycler II platform and overnight broth culture. Samples yielding discrepant results were subjected to detailed analysis with an in-house PCR and patient note review. A total of 1,428 pooled MRSA screens were tested. Sensitivities and specificities of 85.3% and 95.8% for the Rotor-Gene and 81% and 95.7% for the Smart-Cycler were obtained, compared with broth enrichment. The sensitivity of the BD GeneOhm assay was increased to 100% when the results of in-house PCR and patient note review were taken into account. This study demonstrates that the Rotor-Gene 6000 thermal cycler is a reliable platform for use with the BD GeneOhm assay. It also proves that commercial PCR can be performed direct on pooled samples in selective broth, without the need for overnight incubation.

Reliability of the BD GeneOhm Methicillin-Resistant Staphylococcus aureus (MRSA) Assay in Detecting MRSA Isolates with a Variety of Genotypes from the United States and Taiwan

The BD GeneOhm methicillin-resistant Staphylococcus aureus (MRSA) assay is a molecular screening test for detection of MRSA in nasal colonization. This assay coamplifies the extremity of staphylococcal chromosome cassette mec (SCCmec) and adjacent chromosomal DNA at the SCCmec insertion site. Increasing reports of novel SCCmec types and the diverse genetic backgrounds of MRSA strains prompted us to test the accuracy of the BD GeneOhm MRSA kit with 914 MRSA isolates with a variety of SCCmec types harbored in 21 genetic backgrounds, as determined by the multilocus sequence type (ST). The BD GeneOhm MRSA assay was performed on colony lysates; purified genomic DNA (0.2 pg/μl and 0.2 ng/μl) was tested to confirm negative results from lysates. Of 914 MRSA isolates tested, 911 tested positive (detection rate, 99.7%). The SCCmec types carried by assay-positive isolates were I, II, III, IV, V, V(5C2&5), VI, and VIII and SCCmec composite islands with mec class A and ccr complexes 2 and 4. One of the assay-negative isolates had a community-associated genotype: ST8, SCCmec type IV. However, this was an outlier among the 99.8% (434/435) ST8, SCCmec type IV-containing isolates that tested positive. The two other assay-negative isolates had a health care-associated genotype (ST5); both carried a distinct, uncommon, composite SCCmec type. In summary, the BD GeneOhm MRSA assay had a high rate of detection of MRSA isolates harboring common and uncommon SCCmec types from the United States and Taiwan.

Detection of Methicillin-Resistant Staphylococcus aureus (MRSA) in Specimens from Various Body Sites: Performance Characteristics of the BD GeneOhm MRSA Assay, the Xpert MRSA Assay, and Broth-Enriched Culture in an Area with a Low Prevalence of MRSA Infections

Universal surveillance upon patient admission is important in reducing the transmission of methicillin-resistant Staphylococcus aureus (MRSA) and associated disease in hospitals. High costs for the health care system in conjunction with MRSA have promoted the development of rapid screening methods to detect MRSA carriers. This study compared two real-time PCR methods, the BD GeneOhm MRSA assay (BDGO) and the Xpert MRSA assay, with broth-enriched culture to define their performance characteristics and rapidity in an area with low MRSA prevalence. In total, 414 swabs from the nose and 389 swabs from the groin from 425 patients were tested. Of those 425 patients, 378 had swabs from both the nose and groin in parallel. Two hundred thirty-one and 194 patients were randomly assigned to the BDGO group and the Xpert MRSA group, respectively. In general, sensitivity, specificity, and negative predictive value (NPV) were high for the BDGO (100%, 98.5%, and 100%, respectively) and the Xpert MRSA (100%, 98.2%, and 100%, respectively), irrespective of whether or not nasal and inguinal specimens were considered alone or combined. In contrast, the positive predictive value (PPV) was lower: before the resolution of discrepant results, the PPVs for nasal and inguinal specimens alone and combined were 87.5%, 86.7%, and 82.4% for the BDGO and 91.7%, 66.7%, and 92.9% for the Xpert MRSA, respectively. After the resolution of discrepant results, PPVs were 93.8%, 93.3% and 94.1% for the BDGO and 91.7%, 88.9% and 92.9% for the Xpert MRSA, respectively. With the BDGO, 4 of 16 carriers were each identified by nasal or inguinal swabs alone, whereas in the Xpert MRSA group, 4 of 13 carriers were exclusively identified by nasal swabs and 2 of 13 were identified by inguinal swabs alone. Both PCR methods showed no significant difference in the number of discrepant results (odds ratio, 0.70 [P = 0.789]), but specimens from wounds and other body sites (axilla, vagina, and throat) produced discrepancies more often than nasal and groin specimens (odds ratios, 4.724 [P = 0.058] and 12.163 [P < 0.001], respectively). The facts that no false-negative PCR results were detected and increased PPVs were found after the resolution of discrepant results point to PCR as the actual gold standard. Since both sensitivity and NPV were exceptionally high for PCR, backup cultures may, therefore, be unnecessary in an area with low prevalence and with a preemptive isolation strategy but may still be useful for PCR-positive specimens because of the lower PPV for both methods and the possibility of susceptibility testing. The median time for analysis, including extraction, hands-on time, and actual PCR was 2 h 20 min for the Xpert MRSA versus 5 h 40 min for the BDGO. Concerning reporting time, including administration and specimen collection, the Xpert MRSA was faster than the BDGO (7 h 50 min versus 17 h).

Multicenter Evaluation of the LightCycler Methicillin-Resistant Staphylococcus aureus (MRSA) Advanced Test as a Rapid Method for Detection of MRSA in Nasal Surveillance Swabs

The rate of methicillin-resistant Staphylococcus aureus (MRSA) infection continues to rise in many health care settings. Rapid detection of MRSA colonization followed by appropriate isolation can reduce transmission and infection. We compared the performance of the new Roche LightCycler MRSA advanced test to that of the BD GeneOhm MRSA test and culture. Double-headed swabs were used to collect anterior nasal specimens from each subject. For both tests, DNA was extracted and real-time PCR was performed according to manufacturer's instructions. For culture, one swab of the pair was plated directly to CHROMagar MRSA. The swab paired with the BD GeneOhm MRSA test was also placed into an enrichment broth and then plated to CHROMagar MRSA. Colonies resembling staphylococci were confirmed as S. aureus by standard methods. Discrepant specimens had further testing with additional attempts to grow MRSA as well as sample amplicon sequencing. Agreement between results for the two swabs was 99.3% for those with valid results. A total of 1,402 specimens were tested using direct culture detection of MRSA as the gold standard; 187 were culture positive for MRSA. The LightCycler MRSA advanced test had relative sensitivity and specificity of 95.2% (95% confidence interval [CI]: 91.1% to 97.8%) and 96.4% (95% CI: 95.2% to 97.4%), respectively. The BD GeneOhm assay had relative sensitivity and specificity of 95.7% (95% CI: 91.7% to 98.1%) and 91.7% (95% CI: 90.0% to 93.2%), respectively. Following discrepancy analysis, the relative sensitivities of the LightCycler MRSA advanced test and the BD GeneOhm MRSA assay were 92.2 and 93.2%, respectively; relative specificities were 98.9 and 94.2%, respectively. Specificity was significantly better (P<0.001) with the LightCycler MRSA advanced test. The sensitivity of direct culture was 80.4%. The LightCycler MRSA advanced test is a useful tool for sensitive and rapid detection of MRSA nasal colonization.

Rapid Detection of Methicillin-Resistant Staphylococcus aureus (MRSA) in Diverse Clinical Specimens by the BD GeneOhm MRSA Assay and Comparison with Culture

The efficacy of the BD GeneOhm methicillin-resistant Staphylococcus aureus (MRSA) assay was assessed by analyzing nasal swabs and swabs from other body sites for the presence of MRSA in a low-prevalence area. From 681 patients with a high risk for MRSA carriage, 1,601 specimens were collected and transported in Amies agar. After discordant analysis, the sensitivity, specificity, positive predictive value, and negative predictive value of the BD GeneOhm MRSA assay were 84.3%, 99.2%, 88.4%, and 98.9%, respectively, compared to culture.

Detection limits of a rapid MRSA detection assay based on multiplex real-time PCR

I wish to report the results of a study for the limits of detection of a rapid methicillin-resistant Staphylococcus aureus (MRSA) detection assay based on a multiplex realtime polymerase chain reaction (PCR) (BD GeneOhm MRSA assay, Fukushima, Japan), which was reported in the Journal of Infection and Chemotherapy, Volume 15 (No. 4), 2009 [1]. ATCC 33591 (MRSA) was recovered on Mueller Hinton agar by overnight incubation at 37 C. Colonies were picked from the agar, adjusted to Mcfarland 0.5, and diluted to 10–10 colony-forming units (CFU)/ml (corresponding to approximately 10–10 CFU/reaction) by the sample buffer (Tris-EDTA buffer) of the BD GeneOhm MRSA assay kit [1]. The BD GeneOhm MRSA assay was performed four times at about the same concentration to determine the limits of detection. Table 1 shows the result of the tests. All tests were positive with 10–10 and 10 CFU/reaction; however, only half of the tests were positive with at a reaction concentration of 10 CFU. Although the results of the study show that at least 10 CFU/reaction is necessary to detect MRSA stably by the BD GeneOhm MRSA assay, compilation of data and further study with clinical samples are needed. Reference

Comparison of the BD™ GeneOhm MRSA assay, broth enrichment culture and chromID™ MRSA for detection of methicillin-resistant Staphylococcus aureus from inter-hospital intensive care transfer patients

The objective of the present study was to compare the current chromogenic methicillin-resistant Staphylococcus aureus (MRSA) agar plate culture method with broth enrichment and the BD GeneOhm MRSA assay. Another key objective was to determine whether two admission surveillance swabs collected 1 h apart would reliably detect MRSA colonisation in patients transferred to a tertiary referral intensive care unit from other hospitals compared with the current routine method of two samples collected 24 h apart. In total, 593 swabs from 102 consecutive patients transferred from another hospital to the Princess Alexandra Hospital ICU were screened for the MRSA using nose and groin swabs collected on admission, 1 h and 24 h after admission. The non-selective broth enrichment step produced results in complete concordance with the existing method without an increase in sensitivity. The GeneOhm MRSA assay demonstrated 100% sensitivity, 97% specificity and 100% negative predictive values. The initial positive predictive value of this assay, however, was only 28%, largely due to the low prevalence of MRSA. Despite this low positive predictive value and because of the demonstrated 100% negative predictive value, the use of this assay could significantly improve turn-around times of surveillance screens in our laboratory by obviating the need for culture of over 90% of MRSA screening swabs. Positive polymerase chain reaction results require confirmation by culture, given that phenotypical characterisation of isolates is required for infection prevention and control. Comparison of the two screening collection timings in determining MRSA carriage could not be answered, due to insufficient positive results in the study group.

Evaluation of a commercial MRSA assay when multiple MRSA strains are causing epidemics

Rapid and reliable diagnostic methods are needed to control methicillin-resistant Staphylococcus aureus (MRSA) transmission. We studied the BD GeneOhm MRSA Assay which is based on one specific amplification product at the junction of the right extremity sequence of the staphylococcal cassette chromosome mec (SCCmec) and the chromosomal sequence of orfX of S. aureus. The test was applied on 95 clinical isolates in Finland: 83% were positive. The isolates giving negative results represented several pulsed-field gel electrophoresis (PFGE) types and harboured SCCmec types IV, V, VI or were new types with different combinations of ccr genes.

Cost-Effective Frozen Master Mix Modification of a Commercial Methicillin-Resistant Staphylococcus aureus PCR Assay

The expense inherent to molecular diagnostics may be an overriding concern for a variety of clinical laboratories in the development of PCR-based methicillin-resistant Staphylococcus aureus (MRSA) active surveillance programs. BD GeneOhm MRSA assay master mix was reconstituted, aliquoted into SmartCycler tubes in 25-microl volumes, and frozen at -70 degrees C. One hundred percent of archival nasal swab lysates yielded the expected PCR results when incubated in master mix frozen for 1, 2, 3, and 4 weeks. A 98.8% concordance of the final result was observed upon prospective PCR analysis of 320 clinical lysates utilizing freshly reconstituted master mix and 2-week-frozen master mix. Initial unresolved rates generated by frozen master mix and freshly reconstituted master mix differed by 1.6% (P = 0.16). Of 50 MRSA-positive lysates, the titers of 32 (64%) were determined to the same value upon initial tandem frozen master mix and freshly reconstituted master mix utilization; the titers of an additional 14 were determined to the same value upon repeat testing. Frozen master mix maintains potency for at least 4 weeks, facilitating detection of MRSA from nasal swab lysates, and may decrease the amount of unused reagent up to an average of 33%.

A Common Variant of Staphylococcal Cassette Chromosome mec Type IVa in Isolates from Copenhagen, Denmark, Is Not Detected by the BD GeneOhm Methicillin-Resistant Staphylococcus aureus Assay

Rapid tests for detection of methicillin-resistant Staphylococcus aureus (MRSA) carriage are important to limit the transmission of MRSA in the health care setting. We evaluated the performance of the BD GeneOhm MRSA real-time PCR assay using a diverse collection of MRSA isolates, mainly from Copenhagen, Denmark, but also including international isolates, e.g., USA100-1100. Pure cultures of 349 MRSA isolates representing variants of staphylococcal cassette chromosome mec (SCCmec) types I to V and 103 different staphylococcal protein A (spa) types were tested. In addition, 53 methicillin-susceptible Staphylococcus aureus isolates were included as negative controls. Forty-four MRSA isolates were undetectable; of these, 95% harbored SCCmec type IVa, and these included the most-common clone in Copenhagen, spa t024-sequence type 8-IVa. The false-negative MRSA isolates were tested with new primers (analyte-specific reagent [ASR] BD GeneOhm MRSA assay) supplied by Becton Dickinson (BD). The ASR BD GeneOhm MRSA assay detected 42 of the 44 isolates that were false negative in the BD GeneOhm MRSA assay. Combining the BD GeneOhm MRSA assay with the ASR BD GeneOhm MRSA assay greatly improved the results, with only two MRSA isolates being false negative. The BD GeneOhm MRSA assay alone is not adequate for MRSA detection in Copenhagen, Denmark, as more than one-third of our MRSA isolates would not be detected. We recommend that the BD GeneOhm MRSA assay be evaluated against the local MRSA diversity before being established as a standard assay, and due to the constant evolution of SCCmec cassettes, a continuous global surveillance is advisable in order to update the assay as necessary.

Multicenter Evaluation of the Cepheid Xpert Methicillin-Resistant Staphylococcus aureus (MRSA) Test as a Rapid Screening Method for Detection of MRSA in Nares

The first U.S. multicenter clinical trial to assess the performance of the Cepheid Xpert MRSA assay (Xpert MRSA) was conducted. The assay is a qualitative test designed for the rapid detection of methicillin-resistant Staphylococcus aureus (MRSA) directly from nares swabs. This novel test combines integrated nucleic acid extraction and automated real-time PCR for the detection of a MRSA-specific signature sequence. A total of 1,077 nares specimens were collected from seven geographically distinct health care sites across the United States with prevalence rates ranging from 5.2% to 44%. Nares specimens were tested by (i) the Xpert MRSA assay, (ii) direct culture on CHROMagar MRSA medium (direct CM culture), and (iii) broth-enriched culture (Trypticase soy broth with 6.5% sodium chloride) followed by plating onto CHROMagar MRSA medium (broth-enriched CM culture). When direct CM culture was designated the reference method, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the Xpert MRSA assay were 94.3%, 93.2%, 73.0%, and 98.8%, respectively. When broth-enriched CM culture was used as the reference method, the clinical sensitivity, specificity, PPV, and NPV of the Xpert MRSA assay were 86.3%, 94.9%, 80.5%, and 96.6%, respectively. The BD GeneOhm MRSA (BDGO) assay was performed as a comparative molecular method. No statistical performance differences were observed between the Xpert MRSA and BDGO assays when they were compared to culture methods. From this large-scale, multicenter clinical comparison, we conclude that the Xpert MRSA assay is a simple, rapid, and accurate method for performing active surveillance for MRSA in a variety of health care populations.

Comparative evaluation of a rapid MRSA detection assay based on multiplex real-time PCR versus MRSA screening cultures containing egg yolk

Although the Centers for Disease Control and Prevention (CDC) has been recommending the performance of active surveillance culture (ASC) for the prevention of methicillin-resistant Staphylococcus aureus (MRSA) infections and their control since the guideline was issued in 2006, many variant types of MRSA with various characteristics have been found recently. As this change in MRSA characteristics makes it harder to screen MRSA only by cultures, it is expected that ASC will not be sufficient for the prevention of MRSA infections or MRSA infection control. We evaluated the comparative utility of the BD GeneOhm MRSA assay (a rapid MRSA detection test based on a multiplex real-time polymerase chain reaction [PCR] assay; Becton Dickinson, Fukushima, Japan) and MRSA screening cultures containing egg yolk. The results of the BD GeneOhm MRSA assay were as follows: all MRSA strains were positive, including one strain which became positive by retest; all methicillin-resistant S. epidermidis (MRSE) strains and methicillin-sensitive S. epidermidis (MSSE) strains were negative; 11 of 12 methicillin-sensitive S. aureus (MSSA) strains were negative, while 1 strain was positive; ATCC 33591 was positive, and ATCC 29213 was negative. The sensitivity and specificity of the BD GeneOhm MRSA assay were 100% and 97.4%, respectively. Nine egg yolk reaction-negative MRSA strains were found in 50 MRSA strains, and all MRSE, MSSA, and MSSE strains were denied as MRSA on Pourmedia MRSA II (Eiken Chemical, Tokyo, Japan) after 24-h or 48-h incubation at 35 degrees C. The sensitivity and specificity of Pourmedia MRSA II were 82% and 100%, respectively. Similar results were obtained with some other cultures containing egg yolk.

Use of CultureSwab Plus Swabs with Amies Gel Agar for Testing of Naris Specimens with the GeneOhm MRSA Assay

The GeneOhm MRSA assay detects nasal colonization with methicillin-resistant Staphylococcus aureus (MRSA). We compared the use of seeded swabs with liquid Stuart's medium and that of seeded swabs with Amies gel for the assay. Overall, the swabs with liquid Stuart's medium detected significantly greater numbers of MRSA than the swabs with Amies gel (P = 0.0003).