Molecular characterization of methicillin-resistant Staphylococcus aureus with emergence of epidemic clones of sequence type (ST) 22 and ST 772 in Mumbai, India

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 (SCCmec) 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 SCCmec III (25%), 136 were SCCmec IV (34%), and 162 were SCCmec V (41%). All SCCmec III strains were multidrug resistant, and all patients had risk factors. Of the SCCmec 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 SCCmec IV and SCCmec 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 (SCCmec IV) and ST 772 (SCCmec V), both of which feature in Asian studies and may be slowly replacing the multidrug-resistant ST 239 (SCCmec 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.

FIG. 1.

Antimicrobial resistance patterns of MRSA from the laboratory. CIP, ciprofloxacin; GEN, gentamicin; ERY, erythromycin; SXT, trimethoprim-sulfamethoxazole; NET, netilmicin; AMK, amikacin; TET, tetracycline; CLI, clindamycin; RIF, rifampin; CHL, chloramphenicol (resistance data represented as percentages among SCCmec types III, IV, and V).

FIG. 2.

Characteristics of the MRSA strains in the study: PVL gene positivity and patient risk factors.