Investigation of linezolid resistance among methicillin resistant Staphylococcus aureus strains isolated from state hospitals in the East and West coast of Malaysia

Aims: Linezolid, the first available agent of a new antimicrobial class, the oxazolidinones, is broadly effective against drug-resistant gram-positive pathogens which are common causes of infections in hospitalized patients. However, it is not widely available in Malaysian government hospitals and therefore, relatively little is known about the prevalence of linezolid resistance in this background. The main aim of our study was to determine the prevalence of linezolid resistance among a total of 100 strains of methicillin-resistant Staphylococcus aureus (MRSA) isolated in June-October 2012 from two Malaysian state hospitals, namely Hospital Universiti Sains Malaysia (HUSM) and Hospital Pulau Pinang (HPP). The antibiotic susceptibility of the strains was also determined. Methodology and results: The clinical MRSA isolates were tested by the antibiotic strip method for in vitro susceptibility to 6 antibiotics (linezolid, vancomycin, chloramphenicol, clindamycin, erythromycin and oxacillin). Using this method, we report a 2- to 3-fold greater potency of linezolid versus vancomycin, the current treatment of choice for MRSA in these institutions. Three of the isolates, all originating from HPP, showed intermediate resistance to vancomycin (3-8 μg/mL). Four percent of all isolates were resistant to chloramphenicol, 20% were resistant to clindamycin, 33% were resistant to erythromycin and all were resistant to oxacillin. Multiple drug resistance was found in 21 HPP isolates with 3 different non-susceptibility profiles observed. Conclusion, significance and impact study: Based on our data, we would recommend linezolid as an acceptable alternative to vancomycin. Linezolid therapy would be valuable in cases of treatment failure with empirical vancomycin, serious invasive infections caused by vancomycin intermediate S. aureus (VISA) or whenever aggressive vancomycin dosing is not recommended due to toxicity concerns.