Screening Public Surfaces for Methicillin-Resistant Staphylococci

Illnesses resulting from antibiotic-resistant bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), are increasing. Recent evidence shows that pathogens once associated with clinical settings are now contaminating non-clinical environments, including public facilities. While methods of isolation and detection of MRSA in clinical settings are established, methods to detect MRSA in non-clinical environments have not been fully evaluated. Therefore, the aims of this study were to (i) determine the prevalence of methicillinresistant bacteria on surfaces in the non-clinical environment and (ii) compare the efficacy of two specialized media to identify putative MRSA from fomites. Swabs collected from various surfaces were inoculated in Mueller-Hinton broth supplemented with oxacillin (6 mg l). Over 50% of the surfaces were contaminated with antibiotic-resistant bacteria. Six bacteria were isolated and purified from each of the cultures that represented each fomite. These isolates were transferred to CHROMagar and oxacillin resistant screening agar base (ORSAB) media, which are commonly used to identify MRSA. While none of the isolates growing on ORSAB exhibited features diagnostic of MRSA, 47% of the isolates exhibited MRSA-specific characteristics on CHROMagar. To verify the accuracy of the media, the isolates were subjected to multiplex PCR analysis diagnostic for MRSA. All colonies growing on both media were identified as methicillin-resistant Staphylococcus spp., but none were MRSA. Our results indicated that over one-half of the community fomites sampled harbored methicillin-resistant bacteria, which might be of public health importance. However, the characterization of MRSA from environmental fomites using CHROMagar media might not be accurate and must be performed cautiously.