AdeABC efflux pump and resistance of Acinetobacter baumannii against carbapenem

Abstract

To investigate relationship between AdeABC efflux pump and resistance of Acinetobacter baumannii against carbapenem. Methods: Carbapenem-resistant strains were acquired from multistep selection resistance test by meropenem in vitro. The quantitation test for sensitivities of strains before and after induction was determined by the E-test, and carbonylcyanide-m-chlorophenylhydrazone (CCCP) inhibition test was used to screen efflux pump. PCR, sequencing analysis, or real-time PCR was used to analyze the changes of regulatory genes adeR and adeS of the AdeABC efflux pump system, or expressions of adeA, adeB, adeR, and adeS in the strains before and after induction, respectively. Results: The minimal inhibitory concentrations (MICs) of meropenem were at 0.38 μg/mL and 0.25 μg/mL in parental sensitive strain S25595 and S7257, respectively, and the MICs of meropenem for both S25595 and S7257 after induction were more than 32 μg/mL. Compared with parental sensitive strains, the expression level of adeA, adeB, adeR, and adeS mRNA were elevated from 2.45 to 9.44 times, but there were no gene mutations or insertion sequences in the regulatory gene adeS and adeR. Conclusion: High expression of the AdeABC efflux pump system in Acinetobacter baumannii is closely associated with meropenem resistance. The upregulation of adeA and adeB expression is not due to gene mutations in the regulatory gene adeS and adeR and other mechanisms might account for it.