The PCR-based methodology applied to multiple-locus variable numbers of tandem repeat (VNTR) analysis was recently shown to be a useful technique for the molecular typing of clinical isolates of several bacterial species. We have adopted this method for the molecular typing of methicillin-resistant Staphylococcus aureus . Five staphylococcal VNTR loci ( sdr , clfA , clfB , ssp , and spa ) were subjected to analysis, and it was shown that the method allows typing of S . aureus strains with the discriminatory power and reproducibility of pulsed-field gel electrophoresis while at the same time being rapid and applicable to analysis of large numbers of isolates.

Multiple-locus variable-number tandem-repeat analysis (MLVA), a new PCR-based method of typing Staphylococcus aureus , was compared to pulsed-field gel electrophoresis (PFGE), spa typing, and multilocus sequence typing (MLST) on a group of 59 S. aureus (mostly methicillin-resistant) clinical isolates. The aim of the study was to establish possible criteria of clustering MLVA patterns and to check concordance levels between the results produced by MLVA and the three other typing methods. As in our earlier study, MLVA turned out to have discriminatory power similar to that of PFGE. Comparison of data obtained by the two approaches allowed us to propose a 70% or ca. 80% cutoff value of the similarity between two MLVA patterns, depending on a cutoff level applied to interpret the PFGE results, 75% or ca. 90%, respectively. The cutoff values corresponded to the difference of up to six or four bands, respectively, among maximum 14 bands in total produced by two isolates in the analysis. The MLVA clusters matched well those obtained by PFGE, and they were also consistent in general with clusters generated by spa typing and MLST, these latter methods characterized lower resolution. Our results suggest that MLVA may be reliable in shorter-term S. aureus epidemiological studies, including analyses of outbreaks and hospital-to-hospital strain transmission events. Well-known advantages of typing methods based on PCR (low cost, short time, and easiness of performance) make MLVA a method that may be useful in a variety of laboratories, including those performing routine microbiological analyses within medical centers.

The first heterogeneously vancomycin-intermediate Staphylococcus aureus (hVISA) isolates to be identified in Poland were characterized. They were recovered in two Warsaw hospitals and, although in one of these the identification coincided with unsuccessful glycopeptide therapy, the selection conditions and clinical significance of the organisms remain unclear. Molecular typing revealed that the isolates were closely related and belonged to an international methicillin-resistant S. aureus (MRSA) clone known as ‘Iberian’. The analysis of epidemiologically related MRSA isolates and some archival Polish MRSA isolates of the same clone indicated that the hVISA phenotype has been present in the MRSA populations of some hospitals in Poland since at least 1998.