Reduced Daptomycin Susceptibility in Clinical MRSA Isolates Showing Vancomycin MIC Creep Phenomenon

Abstract

Introduction: Infections caused by Methicillin Resistant Staphylococcus aureus (MRSA) are associated with increased morbidity, longer antimicrobial therapy, etc. First option for treating invasive MRSA infections is glycopeptide vancomycin. Daptomycin, a lipopeptide rapidly bactericidal invitro against MRSA, is an acceptable alternative. Aim: To identify MRSA isolates from clinical specimens and assess their vancomycin and daptomycin susceptibility pattern. Materials and Methods: The cross-sectional study was conducted over a period of six months (January 2019 to June 2019) on 90 clinical samples in a rural teaching hospital in Pune, Maharashtra, India, including all samples except sputum received in the Microbiology laboratory. MRSA isolates were tested for vancomycin and daptomycin susceptibility by Epsilometer (E) test Minimum Inhibitory Concentration (MIC) method. Results: Among 90 MRSA isolates, most were from pus (51) followed by Urine (23), Blood (9), followed by Miscellaneous samples (7). Data analysis was done using Statistical Package for the Social Sciences (SPSS) version 16.0 software. All MRSA isolates in this study were susceptible to daptomycin with MIC in the range of 0.25-1 μg/mL with maximum isolates (39) with MIC of 0.38 μg/mL. Vancomycin MIC creep phenomenon was observed in 68 isolates. All these isolates also showed reduced susceptibility to daptomycin. Conclusion: MRSA in hospital set up mandates strict infection control practices in place. Daptomycin can be a good therapeutic alternative to treat infections caused by MRSA keeping in mind its therapeutic limitations and prior vancomycin usage in the same patient. Empirical therapy should always be based on antibiogram pattern. Adherence to hospital antibiotic policy and constant surveillance of antimicrobial resistance is the need of the hour.