iTRAQ-Based Quantitative Proteomic Analysis of Acinetobacter baumannii under Hypoxia and Normoxia Reveals the Role of OmpW as a Virulence Factor

ABSTRACT Acinetobacter baumannii needs to adapt to hypoxia during infection. Understanding its proteome regulation during infection would allow us to determine new targets to develop novel treatments. iTRAQ proteomic analysis of A549 cell infection by the ATCC 17978 strain was performed. A total of 175 proteins were differentially expressed under hypoxia versus normoxia. We selected the hypoxia-downregulated protein OmpW to analyze its role as a virulence factor. The loss of OmpW decreased the adherence and invasion of A. baumannii in these host cells, without affecting its bacterial growth. Moreover, A549 cell viability with ΔOmpW infection was higher than that with the wild-type strain. ΔOmpW presented less biofilm formation. Finally, the minimum lethal dose required by the ΔOmpW mutant was higher than that of the wild-type strain in a murine peritoneal sepsis model, with lower bacterial loads in tissues and fluids. Therefore, OmpW seems to be a virulence factor necessary for A. baumannii pathogenesis. IMPORTANCE Acinetobacter baumannii causes infections that are very difficult to treat due to the high rate of resistance to most and sometimes all of the antimicrobials used in the clinical setting. There is an important need to develop new strategies to combat A. baumannii infections. One alternative could be blocking specific bacterial virulence factors that this pathogen needs to infect cells. Pathogens modulate their protein expression as a function of the environment, and several studies have reported that hypoxia occurs in a wide range of infections. Therefore, it would be interesting to determine the proteome of A. baumannii under hypoxia in order to find new virulence factors, such as the outer membrane protein OmpW, as potential targets for the design of novel therapies.