Colistin was considered as the most effective antibiotic against Acinetobacter baumannii,
a widely-known opportunistic pathogen. In recent years, a number of colistin resistant strains
have also been reported. This work is commenced to investigate the contribution of efflux pumps
toward resistance to colistin-like cyclic polypeptide antibiotics, since the efflux pumps serve as
the escape routes leading to drug-resistance. RNA was extracted from A. baumannii isolates cultured
from samples procured by tracheal aspiration of infected patients. The expressions of
gene(s) that played major roles in the regulation of efflux pump families and involvement of integron
systems were studied using real time PCR. Antimicrobial susceptibility tests were conducted
to investigate antibiotic resistance of the isolates. It was observed that genes coding for sugE,
ydhE, ydgE, mdfA, ynfA and tolC significantly contributed to resistance against colistin antibiotics,
however, no significant transcriptional change was observed in the efflux pump, MexAB-OprM.
Results suggest that A. baumanii readily pumps out colistin via efflux pumps belonging to MATE
and SMR family. Integral role of efflux pumps and integron 1 genetic system was elucidated towards
evolution of multi-drug resistant strain(s). Therefore, for accurate therapeutics, an early detection
of efflux genes is crucial before prescribing against colistin resistant A. baumanii.