Molecular techniques for MRSA typing: current issues and perspectives

Abstract

Staphylococcus aureus has long been recognised as an important pathogen in human disease. Serious staphylococcal infections can frequently occur in inpatients and may lead to dire consequences, especially as to therapy with antimicrobial agents. The increase in the frequency of Methicillin-Resistant Staphylococcus aureus (MRSA) as the causal agent of nosocomial infection and the possibility of emergence of resistance to vancomycin demands a quick and trustworthy characterization of isolates and identification of clonal spread within hospitals. Enough information must be generated to permit the implementation of appropriate measures for control of infection, so that outbreaks can be contained. Molecular typing techniques reviewed in this manuscript include: plasmid profile analysis, analysis of chromosomal DNA after enzymatic restriction, Southern blotting, pulsed field gel electrophoresis (PFGE), techniques involving polymerase chain reaction and multilocus sequence typing (MLST). Repetitive DNA Sequence PCR (rep-PCR) may be used for screening due to its practicality, low cost and reproducibility. Because of its high discriminatory power Pulsed-Field Gel Electrophoresis (PFGE) still remains the gold standard for MRSA typing. New techniques with higher reproducibility and discriminatory power, such as Multi-Locus Sequence Typing (MLST), are appearing. These are mostly useful for global epidemiology studies. Molecular typing techniques are invaluable tools for the assessment of putative MRSA outbreaks and so should be extensively used for this purpose.

The current role of pulsed-field gel electrophoresis in methicillin-resistantStaphylococcus aureus(MRSA) typing and the retrospective identification of outbreaks

“…Many methods are affected by limitations regarding their discriminatory power, reproducibility, stability, or immediate availability in the event of an outbreak [5,6].…”

“…Its discriminatory power is, however, limited by the influences of the complex three-dimensional structure of native plasmids on the mobility of plasmids in gel and the ability of bacteria to spontaneously loose or acquire plasmids [5]. Despite its disadvantages, plasmid profile analysis is still in use today [7].…”

“…More recent methods are based on the analysis of chromosomal DNA such as the interpretation of DNA restriction patterns and Southern blotting followed by hybridisation with DNA probes [5]. These developments culminated in the first successful PFGE analysis that was described for yeast DNA in 1984 [8].…”

“…The discriminatory power of PCR-based approaches, however, is poorer than that of PFGE, especially when it comes to investigating an endemic circulation of clones [5,9]. Commercially available rep-PCR-based typing systems are available as well, such as the DiversiLab microbial typing system (bioMérieux, Nuertingen, Germany) [10].…”

“…The required sequencing of several genes is, however, laborious and expensive [5,15]. For this reason, simpler techniques have been developed such as spa typing.…”