A Clinico-Microbiological Study of Blood Stream Infections in a Tertiary Referral Hospital: Colistin Resistance & Challenges

Carbapenems, frequently used for the treatment of infections caused by Multidrug-resistant (MDR) Gram-negative bacteria (GNB) are being reported with increased resistance rate. Colistin with other antibiotics has emerged as a saviour but inappropriate reporting of colistin susceptibility is a serious clinical concern. To detect the antimicrobial resistance of GNB isolates obtained from blood samples, further, colistin Minimum Inhibitory Concentration (MIC) testing of carbapenem-resistant isolates was done by the Broth Micro-dilution Method (BMD). This prospective study was done in the Department of Microbiology from January 2020 to December 2020. The GNB isolated from blood samples were identified & antimicrobial-susceptibility testing was performed by the Vitek 2 system. Colistin MIC of carbapenem-resistant isolates was done by the BMD method. The data were statistically analysed using SPSS 21. Growth was obtained in 5% of blood samples and 546 (75.8%) of these were GNB including showed significant association with ICU admission, resistance to other classes of antibiotics & mortality. Among the carbapenem-resistant isolates, only seven (2.9%) were found resistant to colistin by the BMD test. Most of these were Klebsiella spp. (71.4%) & obtained predominantly from ICU patients (85.7%). All the carbapenem-resistant isolates were found intermediate sensitive to colistin by the VITEK-2 system. The isolates of GNB were characterized as MDR 323 (59.2%), XDR 164 (30%) and PDR 2 (0.4%). Use of, colistin, should be guided by BMD, the reference method for MIC testing to avoid erroneous reporting of colistin resistance.