Molecular Characterization of Methicillin-Resistant Staphylococcus aureus with Emergence of Epidemic Clones of Sequence Type (ST) 22 and ST 772 in Mumbai, India

Abstract

ABSTRACT A total of 412 methicillin-resistant Staphylococcus aureus (MRSA) strains isolated between October 2006 and June 2009, representing a mixed hospital- and community-associated patient population from Mumbai, India, were evaluated. MRSA was characterized by multiplex PCR amplification of the Panton-Valentine leukocidin (PVL) gene and the mecA gene, staphylococcal cassette chromosome mec (SCC mec ) typing, and multilocus sequence typing (MLST). PCR results were compared with patient risk factors (CDC guidelines) and antimicrobial susceptibility profiles. A total of 395 MRSA strains were mecA positive, and 224 were PVL gene positive. A total of 97 mecA -positive strains were SCC mec III (25%), 136 were SCC mec IV (34%), and 162 were SCC mec V (41%). All SCC mec III strains were multidrug resistant, and all patients had risk factors. Of the SCC mec IV and V strains, 73% were multidrug susceptible and 72% of the associated patients had no risk factors. The multidrug susceptibility and absence of patient risk factors in 72% of cases with SCC mec IV and SCC mec V MRSA demonstrate the presence of community-associated MRSA (CA-MRSA) in Mumbai. Twenty-one percent of these patients had risk factors, signifying CA-MRSA infiltration into hospitals. MLST showed clonal expansion of multidrug-susceptible sequence type (ST) 22 (SCC mec IV) and ST 772 (SCC mec V), both of which feature in Asian studies and may be slowly replacing the multidrug-resistant ST 239 (SCC mec III) in hospitals. The PVL gene-positive methicillin-sensitive S. aureus (MSSA) strains were ST 30 and were postulated to be related to the penicillin-resistant S. aureus phage type 80/81, notorious for its virulence in the 1950s.