The post-antibiotic effects of linezolid against Gram-positive pathogens

OBJECTIVE: To investigate the post-antibiotic effect (PAE) of linezolid against methicillin-resistant and -susceptible staphylococci, vancomycin-resistant and -susceptible enterococci.

METHODS: Clinical strains of Staphylococcus aureus (S. aureus), Staphylococcus epidermidis (S. epidermidis) and Enterococcus faecalis (E. faecalis) were isolated from hospitalized patients at Ege University Medical Faculty Hospital between June and September 2005. This study was made between September and December 2005. The PAE of linezolid was determined at the minimum inhibitory concentration (MIC) and 4 times the MIC concentrations for 60 minutes in Mueller-Hinton Broth (MHB). The duration of the PAE was obtained by following the recovery of bacterial growth in antibiotic free MHB measured colony forming units on Mueller-Hinton agar.

RESULTS: All the straines were susceptible to linezolid. The PAE was greater at 4 times the MIC (0.5 - 2.4 hours) that at the MIC (0 - 1.7 hours) for linezolid against all organisms tested. The PAE for linezolid was slightly higher against E. faecalis strains than other organisms.

CONCLUSION: In this study, it was demonstrated that linezolid had a moderate in vitro PAE against S. aureus, S. epidermidis and E.faecalis strains.