In vitro efficacy of Colistin against multi-drug resistant Pseudomonas aeruginosa by minimum inhibitory concentration

Abstract

Multi-drug resistant bacteria are an important cause of mortality and morbidity. In the management of various infections, timely detection and appropriate treatment, in accordance with the culture and sensitivity reports can help improve the treatment outcome. Colistin is a bactericidal antibiotic which is emerging as a reliable solution for treating infections with multi-drug resistant Gram negative bacilli. The aim of this study was to find out the in-vitro efficacy of colistin against multidrug resistant Pseudomonas aeruginosa isolates by minimum inhibitory concentration. This cross sectional, descriptive study was conducted in the Department of Microbiology, Army Medical College, National University of Sciences and Technology, Islamabad from February 2010 to January 2011. Antimicrobial sensitivity testing was done on Pseudomonas aeruginosa isolated from routine clinical specimens received and the strains which appeared resistant to at least one antimicrobial agent in three or more anti-pseudomonal antimicrobial categories were subjected to the Colistin Etest. The MIC endpoint of colistin was read, as per manufacturer’s instructions (AB Biodisk, Solna, Sweden). The isolates showing MIC of 2µg/ml or less were considered sensitive, those with 4-6µg/ml as intermediate and ≥8µg/ml as resistant. MIC50 and MIC90 of colistin against MDR Pseudomonas aeruginosa was determined. A total of 52 MDR Pseudomonas aeruginosa strains were isolated during the period of the study. The highest percentage was isolated from urine (36%) followed by respiratory tract infections (18%) and pus specimens (20%). The highest percentage of these isolates was found to be susceptible to colistin followed by piperacillintazobactam and cefoperazone-sulbactam. A total of 36(69%) isolates were sensitive, 10(20%) were intermediate and 6(11%) were resistant to colistin by Kirby Bauer disc diffusion method. MIC50 was found to be 1.0µg/ml while MIC90 was 3.0µg/ml. Colistin is a reliable solution in cases of infections with MDR, XDR or PDR Pseudomonas aeruginosa.