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Background: Zinc uptake-regulator (Zur)-regulated lipoprotein A (ZrlA) plays a role in bacterial fitness and overcoming antimicrobial exposure in Acinetobacter baumannii. This study further characterized the zrlA gene and its encoded protein and investigated the roles of the zrlA gene in bacterial morphology, antimicrobial susceptibility, and production of outer membrane vesicles (OMVs) in A. baumannii ATCC 17978., Results: In silico and polymerase chain reaction analyses showed that the zrlA gene was conserved among A. baumannii strains with 97-100% sequence homology. Recombinant ZrlA protein exhibited a specific enzymatic activity of D-alanine-D-alanine carboxypeptidase. Wild-type A. baumannii exhibited more morphological heterogeneity than a ΔzrlA mutant strain during stationary phase. The ΔzrlA mutant strain was more susceptible to gentamicin than the wild-type strain. Sizes and protein profiles of OMVs were similar between the wild-type and ΔzrlA mutant strains, but the ΔzrlA mutant strain produced 9.7 times more OMV particles than the wild-type strain. OMVs from the ΔzrlA mutant were more cytotoxic in cultured epithelial cells than OMVs from the wild-type strain., Conclusions: The present study demonstrated that A. baumannii ZrlA contributes to bacterial morphogenesis and antimicrobial resistance, but its deletion increases OMV production and OMV-mediated host cell cytotoxicity.

Background: Acinetobacter baumannii is an important opportunistic pathogen responsible for various nosocomial infections. The BfmRS two-component system plays a role in pathogenesis and antimicrobial resistance of A. baumannii via regulation of bacterial envelope structures. This study investigated the role of the sensor kinase, BfmS, in localization of outer membrane protein A (OmpA) in the outer membrane and production of outer membrane vesicles (OMVs) using wild-type A. baumannii ATCC 17978, ΔbfmS mutant, and bfmS-complemented strains., Results: The ΔbfmS mutant showed hypermucoid phenotype in the culture plates, growth retardation under static culture conditions, and reduced susceptibility to aztreonam and colistin compared to the wild-type strain. The ΔbfmS mutant produced less OmpA in the outer membrane but released more OmpA via OMVs than the wild-type strain, even though expression of ompA and its protein production were not different between the two strains. The ΔbfmS mutant produced 2.35 times more OMV particles and 4.46 times more OMV proteins than the wild-type stain. The ΔbfmS mutant OMVs were more cytotoxic towards A549 cells than wild-type strain OMVs., Conclusions: The present study demonstrates that BfmS controls production of OMVs in A. baumannii. Moreover, BfmS negatively regulates antimicrobial resistance of A. baumannii and OMV-mediated host cell cytotoxicity. Our results indicate that BfmS negatively controls the pathogenic traits of A. baumannii via cell envelope structures and OMV production.

To elucidate the epidemicity of carbapenem-resistant Acinetobacter baumannii (CRAB), we investigated the antimicrobial susceptibility, the genetic basis of antimicrobial resistance, and the ability to form biofilms of 147 CRAB isolates collected between 2013 and 2015 from a Korean hospital based on sequence types (STs). Six different STs were identified: ST191 (n=47) and ST208 (n=36) were clones that had already been identified in the study hospital, whereas ST229 (n=28), ST369 (n=18), ST357 (n=17), and ST552 (n=1) were previously unknown. All the CRAB isolates exhibited an extensively drug-resistance. Twelve isolates, including ST191 and ST208, were resistant to tigecycline, and two were resistant to colistin. All the isolates carried ISAbaI-bla OXA-23 structures. The presence of the armA gene and/or a combination of aminoglycoside-modifying enzyme genes (aacC1, aadA1, aacA4, aphA1, and aphA6) was responsible for high-level resistance to aminoglycosides (minimal inhibitory concentrations≥256mg/L). All the ST229 isolates carried the bla PER-1 gene, whereas all the ST357 and ST369 isolates carried both aacA4 and aadA1. The ST229 isolates exhibited the greatest tendency to form biofilms, whereas the ST369 isolates exhibited significantly less tendency to form biofilms than other isolates. In conclusion, we discovered clonal diversity in the CRAB isolates from the study hospital. The resistant gene profiles and biofilm formation capabilities of the emerging CRAB STs differed from those of the circulating STs. The potential relationship between these genotypic and phenotypic traits and the epidemic capacity of CRAB STs requires further investigation., (Copyright © 2018 Elsevier B.V. All rights reserved.)