Molecular genetic characterization of methicillin-resistant Staphylococcus aureus isolates recovered from Moscow clinics

Methicillin-resistant Staphylococcus aureus (MRSA) is the causative agent of nosocomial infections observed worldwide. The goal of this work was to study the genetic variations in MRSA isolates recovered from Moscow clinics and compare various methods of molecular typing (multiplex PCR, SNP genotyping based on the determination of single-nucleotide polymorphisms). A total of 62 epidemiologically unrelated hospital-acquired MRSA isolates were studied. A previously described multiplex PCR assay was utilized for the molecular typing of staphylococcal cassette chromosome mec (SCCmec). SNP genotyping that targets the seven sequences in five housekeeping genes (arcC162, arcC210, aroE132, gmk123, tpi241, tpi243, and yqiL333) was employed. Primer extension was used to screen single nucleotide variants followed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Multilocus sequence typing (MLST) was used as a reference assay. Most MRSA isolates (93.6%) were assigned to the clonal complex (CC) 8 disseminated worldwide. Three MRSA isolates (4.8%) proved to belong to CC1. The following correlation was established in this study between SCCmec cassette types and sequence types (STs): ST8-MRSA carried SCCmec type IV and ST239-MRSA carried type-III a SCCmec. Four SNP groups associated with certain SCCmec types were also identified. The developed SNP genotyping assay aided by MALDI-MS enables the rapid genotyping of S. aureus isolates according to their clonal types.