Detection of In-vitro activity of Linezolid in Methicillin Resistant Staphylococcus aureus infections by E-test

Aim: To determine the in-vitro activity of linezolid in methicillin resistant Staphylococcus aureus. Material and Methods: Samples such as pus, sputum, ear swab, pleural fluid that were received in microbiology laboratory were included in the study. Gram staining was performed on all the samples. Smears showing gram positive cocci in clusters were considered. 100 strains of Staphylococci were sub-sequently processed and identified using standard microbiological methods. Staphylococcus aureus so identified were subjected to screening for methicillin resistance using oxacillin disc (1^gm) and also in-vitro activity of linezolid by Kirby-Bauer disc diffusion method. Subsequently minimum inhibitory con-centration for linezolid was determined by E test using Hi-Comb strips obtained from Hi- Media. Results: Out of 100 strains of Staphy-lococcus aureus isolated, 42 (42%) were methicillin resistant and 58 (58%) were methicil¬lin sensitive. Majority of methicillin resistant Staphylococcus aureus isolated were from pus (35) followed by sputum (7). Among the 42 strains of methicillin resistant Staphylococcus aureus isolated, sensitivity to linezolid (30mcg) was 87.71% and minimum inhibitory concentration was in the range of 0.1 - 1 ^gm/ml.Conclusion: Linezolid is a novel alternative drug to vancomycin in the treatment of severe methicillin resistant Staphylococcus aureus infections