Detection of Colistin Resistance in Gram Negative Pathogens: A One Year Cross-sectional Study in a Tertiary Care Centre in Northeast India

Background: Indiscriminate use of colistin for gram-negative infections has led to increase incidence of colistin resistance. The problem of nosocomial infections especially caused by multi-drug-resistant gram-negative bacteria (MDR-GNB), particularly Acinetobacter baumannii, Pseudomonas aeruginosa and Klebsiella pneumoniae is a matter of great concern. This study was conducted to find out the prevalence of colistin resistant gram-negative isolates from patients attending outdoor patient department (OPD), those admitted in wards and Intensive care unit from a Tertiary care centre in North-East India. Materials and Methods: Clinical samples obtained were processed using standard microbiological methods. The gram-negative isolates showing colistin resistance by Kirby- Bauer’s disc diffusion method were included and further subjected for MIC (minimum inhibitory concentration) testing by VITEK-2 system followed by confirmation by Broth microdilution method. Results: Colistin resistance was observed in 26 isolates out of 1040 gram-negative isolates using Broth microdilution method. The MIC values varied from 8 to ≥ 32 μg/ml. Majority of them belong to Pseudomonas species followed by Acinetobacter species and were highly resistant to ß-lactams, aminoglycosides, fluoroquinolones. Conclusion: This study highlights an increasing trend of colistin resistance amongst multidrug resistant (MDR) gram-negative isolates warranting routine screening for colistin resistance to guide appropriate therapy for future use.