Relationships between relative expression of RND efflux pump genes, H33342 efflux activity, biofilm-forming activity, and antimicrobial resistance in Acinetobacter baumannii clinical isolates.

Various mechanisms underlying antimicrobial resistance in Acinetobacter baumannii have been reported. There exists controversy regarding the relationships between efflux pump activity, biofilm formation, and antimicrobial resistance in A. baumannii. In this study, we investigated the relative expression of RND efflux pump genes, H33342 efflux activity, and biofilm-forming activity in 120 A. baumannii clinical isolates, examined their potential relationships with one another, and then statistically analyzed their effects on antibiotic resistance. High adeB expression and high H33342 efflux activity were correlated with low biofilm-forming activity. High adeB expression was significantly correlated with resistance to tigecycline and cefotaxime, but not with the multidrug resistance (MDR) phenotype. Importantly, only high adeJ expression was significantly correlated with the MDR phenotype, and was observed to be correlated with resistance to various antibiotics. However, we found no significant correlation between adeJ expression and biofilm-forming activity. Further, adeG expression was found to not be correlated with antibiotic resistance and biofilm-forming activity. The results of multivariate analysis showed that adeB overexpression and high H33342 efflux activity are related to biofilm-forming activity, and only adeJ overexpression is significantly associated with the MDR phenotype, highlighting the importance of adeJ overexpression.