Purpose: The purpose of this study was to determine the diversity and distribution of various virulence factors in MRSA and MSSA isolates.
Methods: In this study, we have compared a wide range of extracellular enterotoxin genes and virulence factors of 2 MSSA and 17 MRSA isolates from Pakistan. Chromosomal DNA isolated from bacterial cultures grown in Mueller-Hinton broth at 35°C were subjected to the pulsed-field gel electrophoretic (PFGE), PCR analysis, and sequencing and comparison of spa gene PCR products with known spa-types.
Results: Seventeen MRSA and two MSSA isolates exhibited 10 different PFGE patterns. A group of six and five MRSA isolates represented two major PFGE groups, respectively, indicating their clonal selection. PCR analysis of the 11 adhesin genes (fnbA, fnbB, clfA, clfB, can, sdrC, sdrD, sdrE, bbp, ebpS, and map-eap) indicated the presence of 7 common genes (bbp, cna, clfA, clfB, fnbA, fnbB, and map-eap,) in both, MRSA and MSSA isolates. Of the 19 toxin genes tested (edin, eta, etb, hla, hlb, hld, hlg, hlg2, pvl, sea, seb, sec, sed, see, seg, seh, sei, sej, and tst), 10 genes (hla, hlb, hld, hlg, pvl, sed, see, seg, seh, tst) were common in both, the MRSA and MSSA isolates. Five other virulence genes (arcA, cfb, chp, ica, and v8) were tested and only two (cfb, v8) were common among all the isolates. The spa-typing revealed 8 different spa-types, six of the MRSA strains could not be typed. The findings indicated that majority of the virulence gene markers were commonly present in MSSA and MRSA isolates.
Significance: Distribution of the virulence gene patterns and the prevalence of these genes in MSSA and MRSA isolates aids in our understanding of why MRSA strains are more pathogenic than MSSA strains. The results of this investigation will also be helpful in controlling future S. aureus outbreak infections.