Colistin resistance among multidrug resistant gram negative bacteria isolated from cancer patients from Chennai, South India

Background: Colistin is the effective last line drug used for the treatment of infections caused by multidrug resistant (MDR) Gram negative bacteria (GNB). Colistin resistance is on rise and reported worldwide. Colistin resistance among MDR GNB is crucial due to lack of antibiotics for the treatment. This problem is of particular concern among cancer patients, who are more prone to MDR infections and are often treated with colistin. There is a paucity of data in colistin resistance among cancer patients. Hence, the present work was designed to study the prevalence of colistin resistance among MDR GNB isolates from cancer patient and screen for plasmid mediated colistin resistant determinant mcr-1. Methods and materials: A total of 440 clinical GNB isolates from cancer patients were subjected to Antibiotic sensitivity testing. Further Multidrug resistant isolates were screened for colistin resistance by inoculating into Super-polymyxin plate. The isolates grown on the screening medium were tested for minimum inhibitory concentration (MIC) by broth micro dilution method for colistin. Colistin resistant isolates were screened for mcr-1 gene and the genes encoding for carbapenemases, ESBLs and PMQR determinants by PCR amplification. Results: 234/440 (53%) isolates were found to be MDR. 15/234 (6%) isolates grew on super-polymyxin plate. 11/15 (73%) isolates grown on screening plate were colistin resistant and their Colistin MIC ranged from 4–128 μg/mL of which 6 (55%), 4 (36%) and 1 (9%) isolate were P.aeruginosa, K.pneumoniae and E.coli respectively. mcr-1 gene was absent in all colistin resistant isolates. Of ESBL genes 5/11 (45%), 3/11 (27%) and 3/11 (27%) isolates harboured blaCTXM GP1, blaTEM and blaSHV genes respectively. 8/11 (72%) isolates hourboured aac(6′)-IB-cr. 2/11 (18%) isolates harboured qnrB. 4/11 (36%)colistin resistant isolates were found to be carbapenem resistant of which 1/4 (25%) isolates harboured blaNDMgene, 2/4 (50%) isolates harboured blaoxa48like gene and 1/4 (25%) isolate co-harboured blaNDM and blaoxa48like genes. Conclusion: The present study documents the emergence of colistin resistance among MDR GNB isolates from cancer patients. 2.5% isolates were resistant to colistin. Mcr-1gene was absent in all isolates in the current study. Even though the prevalence is low, the results are alarming since colistin resistance in MDR GNB may lead to rise of extremely drug resistant (XDR) isolates which increase mortality and morbidity in cancer patients.