| Summary: | <i>Acinetobacter baumannii</i> is a nosocomial human pathogen of increasing concern due to its multidrug resistance profile. The outer membrane protein A (OmpA) is an abundant bacterial cell surface component involved in <i>A. baumannii</i> pathogenesis. It has been shown that the C-terminal domain of OmpA is located in the periplasm and non-covalently associates with the peptidoglycan layer via two conserved amino acids, thereby anchoring OmpA to the cell wall. Here, we investigated the role of one of the respective residues, D268 in OmpA of <i>A. baumannii</i> clinical strain Ab<sub>169</sub>, on its virulence characteristics by complementing the Δ<i>ompA</i> mutant with the plasmid-borne <i>ompA</i><sub>D268A</sub> allele. We show that while restoring the impaired biofilm formation of the Δ<i>ompA</i> strain, the Ab<sub>169</sub><i>ompA</i><sub>D268A</sub> mutant tended to form bacterial filaments, indicating the abnormalities in cell division. Moreover, the Ab<sub>169</sub> OmpA D268-mediated association to peptidoglycan was required for the manifestation of twitching motility, desiccation resistance, serum-induced killing, adhesion to epithelial cells and virulence in a nematode infection model, although it was dispensable for the uptake of β-lactam antibiotics by outer membrane vesicles. Overall, the results of this study demonstrate that the OmpA C-terminal domain-mediated association to peptidoglycan is critical for a number of virulent properties displayed by <i>A. baumannii</i> outside and within the host.
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