CONTRIBUTION OF UNCHARACTERIZED GENES TO Acinetobacter baumannii ENVELOPE FUNCTIONS

GIACONE, L; REPIZO G; MORAN BARRIO J

Virtual

Congreso; Congreso conjunto SAIB-SAMIGE 2021; 2021

SAIB-SAMIGE

Acinetobacter baumannii (Ab) is a nosocomial pathogen, of major concern due to its multi-drug resistance (MDR) and the recent appearance of hyper-virulent strains in the clinical setting. The World Health Organization included Ab as a critical priority pathogen for the development of novel antibiotics. Ab pathogenesis is associated with a multitude of potential virulence factors (VF) that remain poorly characterized. It is well known that many bacterial envelope components, such as outer membrane proteins (OMPs) and exopolysaccharides facilitate the establishment of a disease state, the persistence in abiotic surfaces and resistance to antibiotic treatment. We previously reported a bioinformatics prediction of A. baumannii AB5075 genes coding for uncharacterized OMPs with putative roles in the pathophysiology of Ab. Analysis of mutants in the corresponding genes (1) revealed that four of them showed reduced A549 cell adherence and invasion (2), thus indicating virulence roles for the corresponding proteins. Here, we further analyze the physiology of these four mutant strains. First, in silico analysis of the candidate proteins revealed that two of them share high similarity with bacterial domains related to stress response or involved in protein-protein interaction and degradation, with roles in the maintenance of outer membrane integrity. The third protein shares low similarity with a protein involved in biofilm formation in Escherichia coli, while no domain similarity was found for the fourth one. In addition, synteny analysis showed that three of the corresponding genes are in proximity to genes related to stress response or other virulence processes like capsule formation, thus suggesting probable regulatory functions. Based on these analysis, we conducted several assays in order to characterize the surface properties of the mutant strains. All of them showed higher levels of biofilm formation on abiotic surfaces, lower motility in semisolid media, and different colony phenotypes in Congo red assay, as compared to WT. These indicate an altered envelope structure or composition in the mutants, leading to the observed phenotypes, and further suggest roles for these OMPs in Ab pathogenesis. The increase in biofilm formation and reductions in cell adherence and invasion supports the notion that Ab can modulate its adhesion properties in order to adapt to diverse environments. Although more work is needed, these results contribute to the understanding of Ab virulence mechanisms, revealing novel possible targets for therapeutic development.1. Gallagher LA et al. (2015) Journal of Bacteriology, 197(12), 2027?2035. https://doi.org/10.1128/JB.00131-152. Giacone L, et al. ?Characterization of outer membrane vesicle-carried proteins as pathogenicity factors from Acinetobacter baumannii?. ISEV 2020 Annual Meeting, Julio 2020.