Influence of Broth Enrichment as well as Storage and Transport Time on the Sensitivity of MRSA Surveillance in the Tropics

Direct growth on blood and screening agar for methicillin-resistant Staphylococcus aureus (MRSA) at a tropical surveillance site was compared with broth enrichment and subsequent growth on selective MRSA agar after international sample transport. In Madagascar, 1548 swabs from an MRSA surveillance study were assessed for growth on Columbia blood agar enriched with 5% sheep blood and MRSA screening agar at the surveillance site with subsequent cold storage of the samples and shipment to Germany. In Germany, 1541 shipped samples were analyzed by non-selective broth enrichment with subsequent culture on MRSA selective agar. A total of 28 MRSA isolates were detected. Of these, 20 strains were isolated from direct culture on blood and MRSA screening agars at the surveillance site, 24 MRSA strains were isolated using the broth enrichment method in Germany, and 16 MRSA strains were identified by both approaches. In spite of the observed die-off of individual strains due to long-term storage and transport, broth enrichment with subsequent screening on MRSA selective agar after international sample shipment led to comparable sensitivity of MRSA detection like streaking on blood and MRSA agar at the tropical surveillance site.