Comparison of antibiotic susceptibility pattern of community- and hospital-acquired methicillin-resistant Staphylococcus aureus with special reference to inducible clindamycin resistance in a tertiary care hospital in southern India

Abstract

Background: Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of nosocomial and community infections. Its prevalence varies markedly across different countries and among hospitals of the same country. Aims and Objectives: To estimate the prevalence of MRSA strains and investigate their antibiogram with special reference to inducible clindamycin resistance. Materials and Methods: All S. aureus isolates obtained from the clinical samples of microbiology laboratory were included in the study. All the isolates were identified by standard methods, and antimicrobial susceptibility testing was performed by Kirby Bauer disk diffusion method. Methicillin resistance was detected by combined cefoxitin and oxacillin disk diffusion method. Results were interpreted as per the Clinical and Laboratory Standards Institute (CLSI) guidelines. Results: A total of 362 S. aureus strains were isolated, of which 36.1% (131/362) isolates were MRSA. Of these, 79.4% (104/131) were hospital-acquired MRSA (HA-MRSA) and 20.6% (27/131) were community-acquired MRSA (CA-MRSA). All the isolates were sensitive to vancomycin. Inducible clindamycin [macrolide-lincosamide-streptogramin B (iMLS B )] resistance (D test) among MRSA isolates was 12.3% (16/131). HA-MRSA isolates showed 12.5% (13/104) D test positivity, as compared to 11.2% (3/27) seen in CA-MRSA isolates. Conclusion: The reported rate of MRSA incidence is alarming. Regular surveillance of hospital-acquired infections, isolation nursing of patients who carry MRSA, monitoring of antimicrobial susceptibility pattern, and formulation of a definite antibiotic policy may be helpful.

Keywords

• Antibiogram
• Clinical and Laboratory Standards Institute
• D test
• methicillin-resistant Staphylococcus aureus