Abstract
Acinetobacter baumannii is an opportunistic pathogen that is multi-drug resistant and frequently responsible for skin and soft tissue infections. These infections predominantly affect trauma, burn, and combat-related wounds. A. baumannii AB5075 is a clinically relevant strain that is hypervirulent due to its enhanced survival and multidrug resistance profile compared with other clinical and laboratory strains. Treatment options for skin and soft tissue infections caused by A. baumannii AB5075 are diminishing due to extensive antibiotic resistance. Hence, this study aimed to identify novel therapeutic targets to combat A. baumannii AB5075 with an in vitro biofilm and in vivo murine skin abscess model. Using transposon sequencing, a transposon mutant library was screened across both conditions, revealing several genes that were conditionally essential for A. baumannii survival. In total, 551 genes (14.14% of all genes) were identified as conditionally essential and 643 genes (16.50% of all genes) as probably conditionally essential for A. baumannii survival in the biofilm environment. Fewer genes were identified as essential for A. baumannii survival in the murine skin abscess model. In total, 3 genes (0.08% of all genes) were identified as conditionally essential and 54 genes (1.40% of all genes) as probably conditionally essential in the skin abscess environment. Comparison of both models revealed ABUW_1371 to be essential for A. baumannii under both the biofilm and murine abscess conditions. It has been reported that ABUW_1371 encodes a putative YaaA protein. Using a transposon insertion mutant, the essentiality of the putative YaaA protein (ABUW_1371) in A. baumannii AB5075 was validated. This was evident with A. baumannii exhibiting a reduced bacterial burden compared to wild type in both the competitive index biofilm assay and the murine abscess model. The function of the putative YaaA protein (ABUW_1371) was confirmed using time-kill assays with hydrogen peroxide where the transposon mutant exhibited increased sensitivity to hydrogen peroxide compared with wild type at sub-inhibitory concentrations. Overall, this study identifies conditionally essential genes required for A. baumannii survival under both a murine skin abscess and biofilm condition. Collectively, these findings provide insight into genes that could be exploited as novel therapeutic targets. Of these genes, the putative YaaA (ABUW_1371) protein is a promising candidate for the development of therapeutic inhibitors, aimed at inhibiting oxidative stress defence mechanisms of A. baumannii AB5075 to combat biofilm-associated skin infections.