Molecular Characterization of Methicillin-resistant Staphylococcus aureus and the Discovery of Novel Spa-Types

Introduction: Methicillin-resistant Staphylococcus aureus (MRSA) isolates pose a serious threat to public health and cause minor, serious, and life-threatening infections. Apart from being present in hospital (HA-MRSA) and community settings (CA-MRSA), MRSA from food-producing and companion animals has, also, been shown to cause infection in humans. In this study, we have compared pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), staphylococcal cassette chromosome mec (SCCmec) typing, and spa typing profiles of 19 Panton-Valentine leucocidin (PVL)-positive HA- and CA-MRSA isolates.

Purpose: In this study, we have determined the molecular diversity of six PVL-positive CA-MRSA and 13 HA-MRSA isolates with respect to their PFGE, MLST, SCCmec, and spa typing profiles.

Methods: The antimicrobial susceptibility and DNA fingerprinting profiles of MRSA isolates were used to determine the similarity index among MRSA isolates. PCR and sequencing was performed to study their MLST, SCCmec, and spa typing profiles. The results were used to assign and compare their MLST- and spa-types with entries in online databases.

Results: Most of the MRSA isolates exhibited resistance to other drugs, including erythromycin gentamicin, kanamycin, oxacillin, and tetracycline. PFGE analysis suggested 10 different pulsotypes. The spa typing indicated seven known spa and two novel spa types. The most prevalent spa type was t030. MLST analysis revealed eight known ST-types, with the most common being ST-239. The majority of the isolates possessed SCCmec type III, alone or in combination with SCCmecIV and V. No correlation between the PFGE patterns (ST- or spa-types) was observed.

Significance: The similarities between CA- and HA-MRSA isolates and the presence of novel spa types indicate an evolutionary trend among MRSA. The data has yielded new and interesting information that could be helpful in understanding the mechanism of evolution, risk assessment of the threats posed by these isolates, and in the development of strategies to manage and control S. aureus infections.