Acinetobacter nosocomialis: Defining the Role of Efflux Pumps in Resistance to Antimicrobial Therapy, Surface Motility, and Biofilm Formation

Abstract

Acinetobacter nosocomialis is a member of the Acinetobacter calcoaceticus-Acinetobacter baumannii (ACB) complex. Increasingly, reports are emerging of the pathogenic profile and multidrug resistance (MDR) phenotype of this species. To define novel therapies to overcome resistance, we queried the role of the major efflux pumps in A. nosocomialis strain M2 on antimicrobial susceptibility profiles. A. nosocomialis strains with the following mutations were engineered by allelic replacement; ΔadeB, ΔadeJ, and ΔadeB/adeJ. In these isogenic strains, we show that the ΔadeJ mutation increased susceptibility to beta-lactams, beta-lactam/beta-lactamase inhibitors, chloramphenicol, monobactam, tigecycline, and trimethoprim. The ΔadeB mutation had a minor effect on resistance to certain beta-lactams, rifampicin and tigecycline. In addition, the ΔadeJ mutation resulted in a significant decrease in surface motility and a minor decrease in biofilm formation. Our results indicate that the efflux pump, AdeIJK, has additional roles outside of antibiotic resistance in A. nosocomialis.

Keywords: Acinetobacter; RND-efflux; antimicrobial resistance; biofilm; motility.

Figure 1

Surface motility of wild-type M2 and efflux mutants. Wild-type M2 and the isogenic adeB and adeJ mutants were assayed for surface motility as described in the Materials and Methods. In (A), motility of the indicated strains is shown after 14 h at 30°C. Motility was quantitated from 4 separate experiments at 30°C (B) and 37°C (C). Error bars represent standard deviation of the mean. N.S. indicates a p-value > 0.05.

Figure 2

Biofilm formation. Wild-type M2 and the isogenic adeB and adeJ mutants were assayed for biofilm formation in microtiter wells grown at 30 or 37°C for 24 h. Values represent crystal violet staining/cell density (A₅₈₅ / A₆₀₀) ratio and error bars represent standard deviation of the mean. N.S. indicates a p-value > 0.05.