Pan-resistance among gram-negative clinical isolates at a tertiary care hospital in south India

Background: The emergence of multi and pan resistance among Gram negative bacteria in the last decade has forced the medical community in using infrequently used antimicrobials in treating these infections. Methods: The present study was designed to look into the activity of certain older antimicrobial agents against Gramnegative clinical isolates resistant to all common antibiotics including carbapenams. Members of enterobacteriaceae family, Acinetobacter species and Pseudomonas aeruginosa isolated and identified in our laboratory during 2011 were included in the study. The antimicrobial susceptibility testing was done as per Clincial and Laboratory Standards Institute (CLSI) guidelines by disc diffusion technique. Results: From January-December 2011, out of a total of 11,658 samples processed, 157 (1.3%) isolates of Gramnegative bacilli were resistant to all beta-lactams, carbapenem, fluroquinolones and aminoglycosides. E.coli was the predominant isolate (n=50; 31.8%) followed by Klebsiella (n=37, 23.6%); 28 (17.8%) isolates were acinetobacter species. P. aeruginosa constituted 17 separate isolates other than the above 157 isolates. Of the unconventional agents tested, polymyxin B was the most effective agent with 33.1% strains sensitive to it and another 5/17 (29.4%) of P. aeruginosa isolates. Other agents in the decreasing order of sensitivity were chloramphenicol (25.5%), tetracycline and nitrofurantoin (14%) each, and cotrimaxazole (5.7%). Conclusions: Our study has highlighted the importance of including certain not-so-common antimicrobials in the sensitivity panel, particularly while testing multidrug-resistant isolates since they still possess some degree of activity against such isolates and may prove useful in clinical setting.