AUTHOR=Subhadra Bindu , Kim Jaeseok , Kim Dong Ho , Woo Kyungho , Oh Man Hwan , Choi Chul Hee 

TITLE=Local Repressor AcrR Regulates AcrAB Efflux Pump Required for Biofilm Formation and Virulence in Acinetobacter nosocomialis

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=8

YEAR=2018

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2018.00270

DOI=10.3389/fcimb.2018.00270

ISSN=2235-2988

ABSTRACT=<p>Multidrug efflux systems contribute to antimicrobial resistance and pathogenicity in bacteria. Here, we report the identification and characterization of a transcriptional regulator AcrR controlling the yet uncharacterized multidrug efflux pump, AcrAB in <italic>Acinetobacter nosocomialis. In silico</italic> analysis revealed that the homologs of AcrR and AcrAB are reported in the genomes of many other bacterial species. We confirmed that the genes encoding the AcrAB efflux pump, <italic>acrA</italic> and <italic>acrB</italic> forms a polycistronic operon which is under the control of <italic>acrR</italic> gene upstream of <italic>acrA</italic>. Bioinformatic analysis indicated the presence of AcrR binding motif in the promoter region of <italic>acrAB</italic> operon and the specific binding of AcrR was confirmed by electrophoretic mobility shift assay (EMSA). The EMSA data showed that AcrR binds to −89 bp upstream of the start codon of <italic>acrA</italic>. The mRNA expression analysis depicted that the expression of <italic>acrA</italic> and <italic>acrB</italic> genes are elevated in the deletion mutant compared to that in the wild type confirming that AcrR acts as a repressor of <italic>acrAB</italic> operon in <italic>A. nosocomialis</italic>. The deletion of <italic>acrR</italic> resulted in increased motility, biofilm/pellicle formation and invasion in <italic>A. nosocomialis</italic>. We further analyzed the role of AcrR in <italic>A. nosocomialis</italic> pathogenesis <italic>in vivo</italic> using murine model and it was shown that <italic>acrR</italic> mutant is highly virulent inducing severe infection in mouse leading to host death. In addition, the intracellular survival rate of <italic>acrR</italic> mutant was higher compared to that of wild type. Our data demonstrates that AcrR functions as an important regulator of AcrAB efflux pump and is associated with several phenotypes such as motility, biofilm/pellicle formation and pathogenesis in <italic>A. nosocomialis</italic>.</p>