Comparison of the BD GeneOhm Methicillin-Resistant Staphylococcus aureus (MRSA) PCR Assay to Culture by Use of BBL CHROMagar MRSA for Detection of MRSA in Nasal Surveillance Cultures from an At-Risk Community Population

Abstract

We compared the BD GeneOhm methicillin-resistant Staphylococcus aureus (MRSA) PCR assay to culture with BBL CHROMagar MRSA for nasal surveillance among 602 arrestees from the Baltimore City Jail. The sensitivity and specificity were 88.5% and 91.0%, respectively, and after secondary analysis using enrichment broth, they were 89.0% and 91.7%, respectively. Twenty-three of 42 false-positive PCR lysates contained methicillin-susceptible S. aureus.Recent community-associated methicillin-resistant Staphylococcus aureus (MRSA) outbreaks among correctional institution populations have demonstrated the need for improved surveillance (3)(4)(5)17). MRSA surveillance is essential to limit transmission and stem future outbreaks in this setting. While rapid diagnostic testing has been successfully implemented within the health care setting (1,6,10,22), such testing will likely present technical and logistical difficulties for correctional facilities.Trypticase soy broth (TSB) with 6.5% NaCl is considered the reference method for recovery of MRSA from nasal surveillance cultures (20). This method is not timely for programs that wish to implement rapid screening. Selective and differential media such as BBL CHROMagar MRSA (CHROM-MRSA) (BD Diagnostics, Sparks, MD) decrease the time to identification of MRSA from 2 or 3 days to 24 to 48 h, require limited training, and are relatively inexpensive compared to molecular methods (11; BBL CHROMagar MRSA package insert, http://www.bd.com/ds/productCenter/215084.asp). In a multicenter study comparing CHROM-MRSA to conventional culture using 5% sheep blood agar and five methods of susceptibility testing, CHROM-MRSA detected an additional 8% positive samples (11). The performance characteristics of chromogenic media compared with PCR have not been well studied. The BD GeneOhm MRSA PCR assay (BD GeneOhm, San Diego, CA) has proven effective for MRSA surveillance (2, 9, 11, 18) but is currently more costly than CHROM-MRSA.An epidemiologic study of MRSA nasal colonization among newly arrested men provided the opportunity to compare the performance characteristics of these methods for MRSA surveillance.(This study was presented in part at the 107th General Meeting of the American Society for Microbiology, Toronto, Canada, 21 to 25 May 2007.)Subject selection and collection of clinical specimens. The Maryland Department of Corrections and the Institutional Review Board of The Johns Hopkins University School of Medicine approved the study. Enrollment criteria included (i) arrested Ͻ24 h previously, (ii) male, (iii) age 21 years and older, and (iv) processed at the Central Booking Intake Facility in Baltimore, MD. Anterior nasal specimens were obtained using BactiSwab II dual-headed culturettes (Remel, Lenexa, KS) from 602 men. Both swabs were inserted into each nare simultaneously. The swabs were transported at room temperature and stored at 5°C until processing within 24 h of collection. The two swabs were randomly separated in the laboratory. One swab was used for culture and the other for th...

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

“…The utility of these tests, such as the BD GeneOhm MRSA assay (BD-MRSA PCR; BD GeneOhm, San Diego, CA), has been described in numerous publications (2,3,6,17,25). However, performance issues related to "falsepositive" results have been reported by some investigators (2,3,21).…”

“…During an epidemiological study performed on adults that compared chromogenic media and the BD-MRSA PCR for detection of MRSA from anterior nasal specimens (5), 23 MSSA isolates were recovered that were initially identified as MRSA positive by the BD-MRSA PCR in which no MRSA was recovered (6). Isolates (n ϭ 23) were recovered directly from subculture of the enrichment Trypticase soy broth with 6.5% NaCl.…”

“…Donnio et al described a number of MSSA isolates (n ϭ 9) from French hospitals containing partial SCCmec elements without mecA (4) and predicted that PCR assays based on the amplification by primers from the SCCmec-orfX region (i.e., BD-MRSA PCR) would be falsely determined as positive for MRSA. The loss of the methicillin-resistant phenotype due to the partial excision of the SCCmec has been suggested as the mechanism behind the high prevalence of false-positive BD-MRSA PCR results observed in some populations (2,6,17,25). In the original description of what is now the BD GeneOhm MRSA assay, Huletsky et al found that 4.6% of the isolates tested from their worldwide collection displayed this phenomenon (9).…”

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

“…Eight of the 27 PCR-positive/culture-negative wound specimens contained methicillin-sensitive S. aureus (MSSA), a fact which has been observed also by others. For instance, Farley et al (12) reported that 55% of the falsepositive PCR specimens contained MSSA, some of the MSSA lysates being, again, positive upon repeated PCR testing. Likewise, Desjardins et al (9) reported a false-positive PCR result with an MSSA strain (ATCC 25923) carrying an element similar to SCCmec which was inserted in the same integration site as SCCmec.…”

Three-Way Comparison of BBL CHROMagar MRSA II, MRSA Select , and Spectra MRSA for Detection of Methicillin-Resistant Staphylococcus aureus Isolates in Nasal Surveillance Cultures

“…To control the transmission of MRSA in health care facilities, targeted active surveillance cultures and an active infection control program to eliminate or control the spread of MRSA in hospitals are recommended (1,2). The introduction of molecular methods (e.g., PCR) for the detection of MRSA in nasal specimens has improved the reporting time of MRSA and utilization of infection control resources (3)(4)(5). However, not all laboratories can justify the added expense of molecular methods.…”