Screening for mutations in pmrB gene to predict potential colistin resistance among the clinical isolates of multidrug-resistant Acinetobacterbaumannii.

PURPOSE: Infections caused by multidrug-resistant Acinetobacter baumannii (MDR-AB) are a major global problem. Increasing resistance to carbapenems among Acinetobacter baumannii (A.baumannii) has led to using colistin as a last resort. Overuse of colistin will lead to the emergence of colistin resistance as evidenced in the past with other antibiotics. In India, reports of colistin-resistant A.baumannii are emerging. The mutations in the pmrA/pmrB genes may induce colistin resistance. However, increasing the minimum inhibitory concentration (MIC) of colistin and detection of mutations in the pmrB gene may provide information on the possibility of emerging resistance.

METHODS: A total of 50 clinical isolates MDR-AB were subjected to colistin broth microdilution and colistin challenge test. Amongst them, five isolates that had slightly higher MIC were sequenced to detect mutations.

RESULTS: Out of 50 isolates, 24 % were isolated from patients who sustained trauma due to road traffic accidents and the majority of them (96 %) required ventilator support. Twenty-seven (56 %) isolates were from patients who developed ventilator-associated pneumonia. The mortality rate was highest (71.4 %) among sepsis cases. The colistin MIC was in the susceptible range in all the isolates. Amongst the five isolates that had slightly higher MIC, only one had a mutation in the pmrB gene.

CONCLUSION: Due to antibiotic pressure, A.baumannii can develop resistance to colistin through genomic mutation. If this trend continues, colistin therapy will become ineffective. This can cause serious implications in the management, especially in critically ill patients. Through a stringent antimicrobial stewardship program (AMSP) the spread of resistance could be controlled.