Medical Microbiology & Diagnosis

Molecular Methods in Epidemiology of Methicillin Resistant Staphylococcus aureus (MRSA): Advantages, Disadvantages of Different Techniques

Abstract

Judit Szabo

The aim of this review article is to compare molecular typing methods of methicillin resistant Staphylococcus aureus (MRSA) strains. Resistance to methicillin and other beta-lactam antibiotics is caused by the mecA gene, which is situated on a mobile genetic element, the Staphylococcal Cassette Chromosome mec (SCCmec). While hospital acquired (HA)-MRSA strains are typically multi-resistant, community associated (CA)-MRSA strains are by large more susceptible to many antibiotics. More resently multi-resistant livestock associated (LA)-MRSA strains have been recovered from bovine mastitis, but these strains are only prevalent in certain high-risk groups of workers in direct contact with live animals. The epidemiology of MRSA might be investigated by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), spa typing, DNA microarray hybridisation and SCCmec typing. Until recently the most useful technique was the PFGE, which has high discriminatory index, but technically difficult and slow, the portability is limited, and multiple nomenclature and misclassification of some lineages also can occur. The mec (SCCmec) typing has standard nomenclature wich able to distinguish between the HA-MRSA and CA-MRSA strains. The spa typing might be a useful tool for epidemiological studies of MRSA, due to its rapidity, accessibility, high throughput, and standardized nomenclature. The MLST has high discriminatory power, defines core genetic population and also has portability and standard nomenclature, but the weaknessess of this method are the low throughput and high cost. Though, the DNA miroarray hybridization test is the most modern technique, which able to detect of presence of a huge number of genomic loci, but due to the high cost and complexity not preferred in routine practice. Considering all data of these molecular techniques, the most recommended methods are the spa and staphylococcal cassette chromosome mec (SCCmec) typing. Both are informative enough to define particular strain characteristics and utilise standardised nomenclatures, making them applicable globally. Continuous efforts to follow up the changing epidemiology of MRSA infection in humans and animals are necessary, not only for effective infection control and appropriate antibiotic treatment, but also monitoring the evolution of the MRSA clones.