INVESTIGATION OF A METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS (MRSA)OUTBREAK IN AN IRISH HOSPITAL - TRIPLEX PCR AND DNA AMPLIFICATION FINGERPRINTING

Methicillin-resistant Staphylococcus aureus (MRSA) is becoming a probl ematic nosocomial pathogen. A continuing increase in numbers of isolat es is reported from Irish hospitals each year. Preventing cross-infect ion and the further spread of endemic strains requires effective contr ol measures. This necessitates the development of sensitive methods fo r both detection and genetic identification of MRSA isolates. In this study, 48 MRSA strains isolated in the Cork University Hospital were a nalysed between January and July 1995 using a one-tube triplex-polymer ase chain reaction (PCR), wherein three genes, the methicillin-resista nce gene (mecA), femA and the extracellular thermonuclease gene, nuc, were simultaneously amplified. Methicillin-sensitive S. aureus (MSSA) and coagulase-negative staphylococci (CNS) were also tested and the as say was found to be MRSA specific. The genetic relationship among this collection of MRSA isolates was also investigated. A single primer, R W3A, derived from a well-characterized, repetitive sequence found in M ycoplasma pneumoniae produced discriminating DNA fragment arrays with all the study organisms. The patterns were reproducible, even after se veral passages of the isolates. Quantitative analysis of the patterns divided the collection into two main groups, DAF group I representing 48% of the collection and DAF group II a further 19%. The remaining st rains showed unrelated patterns. To fully outline the distribution of MRSA in this area a larger study will be necessary. This paper outline s the applicability of both the identification and fingerprinting tech niques to local strains.