Motif-dependent DNA analysis of a methicillin-resistant Staphylococcus aureus collection

Methicillin-resistant Staphylococcus aureus (MRSA) has become a major nosocomial pathogen in recent years. Once introduced into the hospital environment, MRSA can spread rapidly, and its subsequent treatment is often difficult as it may be simultaneously resistant to several antibiotics. A useful strategy both to identify the source of infection and to monitor specific infecting strains would be beneficial, facilitating the implementation of control and preventive measures. In this study, a typing strategy, based on the amplification of a conserved repeat-motif in the bacterial genome, was applied in a hospital setting to analyse an MRSA collection. Using a fluorescent-labelled oligonucleotide primer RW3A, which annealed to several dispersed short-repeat sequences occurring throughout the bacterial genome, DNA amplification fingerprint patterns were produced by polymerase chain reaction (PCR). Thirty-nine MRSA isolates were successfully analysed using conventional agarose gel electrophoresis and GeneScan technology. The latter method provides a finer resolution, making use of capillary electrophoresis in an ABI Prism 310 genetic analyser. The fluorescent detection approach can facilitate the construction of a fingerprint database which can be accessed for comparison of any isolate. Quantitative analysis of all patterns divided the MRSA isolates into four different groups, based on their RW3A fingerprints. Most of the isolates (88%) were assigned to one of three main groups, while the remaining isolates (12%) comprised a fourth, miscellaneous group.