Comparative Antimicrobial Activities of Linezolid and Vancomycin against Gram-Positive Clinical Isolates from Hospitals in Kuwait

Abstract

Objectives: The increasing prevalence of resistant gram-positive bacteria, emergence of vancomycin-resistant enterococci and the isolation of vancomycin-intermediate resistant Staphylococcus aureus have emphasized the need for new antimicrobial agents to treat infections caused by these organisms. We studied the comparative antimicrobial activities of linezolid, a new and totally synthetic oxazolidinone antibacterial agent and vancomycin against resistant gram-positive clinical isolates from four hospitals in Kuwait. Methods: The organisms were isolated from clinical samples including throat and wound swabs, urine and blood, and identified by cultural and biochemical characteristics. The minimum inhibitory concentration (MIC) of linezolid and vancomycin against S. aureus, coagulase-negative staphylococci, Streptococcus pneumoniae and enterococci was determined by the agar dilution method. Results: Linezolid demonstrated MIC ranges of 0.5–4 mg/l against methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus, 1–4 mg/l against methicillin-resistant coagulase-negative staphylococci (MR-CNS) and methicillin-sensitive coagulase-negative staphylococcal strains, and a narrow range of 0.5–1 mg/l against penicillin-resistant S. pneumoniae (PRSP). The range of vancomycin MICs against MRSA, MR-CNS and PRSP was 0.5–4, 0.5–1 and 0.25–0.5 mg/l, respectively. The MIC values of linezolid and vancomycin against vancomycin-susceptible enterococci were 1–2 and 0.5–4 mg/l, respectively. However, linezolid demonstrated a lower MIC of 2 mg/l against vancomycin-intermediate resistant enterococci and vancomycin-resistant enterococci than vancomycin (MICs of 8 and >512 mg/l, respectively). Conclusion: The results indicated that linezolid demonstrated activity comparable to vancomycin against all staphylococcal, vancomycin-susceptible enterococci and PRSP strains, but demonstrated superior activity against vancomycin-intermediate resistant enterococci and vancomycin-resistant enterococci. In addition, linezolid was highly effective against all multidrug-resistant gram-positive clinical isolates from hospitals in Kuwait.