Presence of the Ade multidrug systems and response to triclosan exposure in Acinetobacter baumannii from animal origins

Abstract

Thirty Acinetobacter baumannii from animal origins were obtained from 210 animal carcasses submitted for post-mortem examination, including dogs (n=112), cats (n=45), rabbits (n=17), birds (n=15), pigs (n=7) and exotic animals (n=14). All the isolates were evaluated for antimicrobial susceptibility with the absence and presence of efflux inhibitors, i.e., reserpine and carbonyl cyanide m-chlorophenylhydrazone (CCCP) and expression profile of important six multidrug efflux systems (i.e., AdeABC, AdeDE, AdeFGH, AdeIJK, AbeM and AmvA). Fifteen isolates expressing different Ade multidrug efflux pumps were selected to determine transcription levels and regulatory mutations. A continuous in vitro exposure experiment with benzalkonium chloride, chlorhexidine, and triclosan was performed in the isolates susceptible to most antibiotics and biocides tested (n=12). The results showed that 70% of the isolates (n=21) were multidrug-resistant, and all expressed AdeIJK. The inhibitory effect of reserpine and CCCP suggested that active efflux pumps using a different type of energy (i.e., ATP and proton-motif force) contribute to the reduced susceptibility to antimicrobials in the isolates. Exposure to triclosan resulted in a spontaneous-mutant derivative, ABJ302-1, exhibiting cross-resistance to 10 of 15 antibiotics tested and resulted in downregulated expression of AdeG and AdeJ in almost all the isolates, which may be affected by the stress response of triclosan.