Adaptation of Acinetobacter baumannii tocolistin exposure: Laboratory Mimicking of aClinical Case

Abstract

Colistin resistance is an emerging threat. Here, we presented the development of colistinresistance in A. baumannii after colistin use on a disease course of a patient. To mimic theeffects of colistin in laboratory conditions, three colistin susceptible A.baumannii isolatedfrom the patient were exposed daily to colistin for up to 40 days. The colistin MICs andpmrABC expressions of each generation were studied. After 25 days of colistin treatment,colistin-resistant A. baumannii was isolated from the intra-abdominal fluid of the patient.During the in vitro study, the expressions of pmrCAB reached the highest level at thegeneration that corresponds to the duration of colistin therapy on the isolation day of theisolate.In conclusion, the duration of colistin exposure is critical for the development of colistinresistance. A. baumannii can develop a stable colistin-resistant phenotype with elevatedMICs and upregulated pmrCAB operon after three weeks of colistin exposure.