Outer membrane protein A contributes to antimicrobial resistance of Acinetobacter baumannii through the OmpA-like domain

Objectives: Acinetobacter baumannii outer membrane protein A (AbOmpA) is involved in bacterial pathogenesis. However, the role of AbOmpA in the antimicrobial resistance of A. baumannii has not been fully elucidated. This study aimed to investigate the role of the OmpA-like domain of AbOmpA in the antimicrobial resistance of A. baumannii. Methods: The MICs of antimicrobial agents for the WT A. baumannii ATCC 17978, DompA mutant, OmpA-like domain- deleted (amino acids 223-356) AbOmpA mutant and single-copy ompA-complemented strain were determined by the Etest method. The MICs of antimicrobial agents for MDR strain 1656-2 and its ΔompA mutant strains were also determined. Results: The ΔompA mutant strain of ATCC 17978 was more susceptible to trimethoprim (>5.3-fold) and other antimicrobial agents tested (<2.0-fold), except tigecycline, than the WT strain. The ΔompA mutant strain of 1656-2 was more susceptible to trimethoprim (>4.0-fold), tetracycline (2.3-fold) and other antimicrobial agents (<2.0-fold), including tigecycline, colistin and imipenem, than the WT strain. The MICs of gentamicin, imipenem and nalidixic acid for the WT ATCC 17978 and ΔompA mutant strains were decreased in the presence of an efflux pump inhibitor. A mutant strain of ATCC 17978 with the OmpA-like domain of AbOmpA deleted was more susceptible (≥2.0-fold) to substrates of the resistance-nodulation-division efflux pumps, including aztreonam, gentamicin, imipenem and trimethoprim, than the WT strain. Conclusions: This study demonstrates that AbOmpA contributes to the antimicrobial resistance of A. baumannii through the OmpA-like domain.