Project description:Analysis of the effect of human pleural fluid on the transcriptome of Acinetobacter baumanii A118 Acinetobacter baumannii (Ab) is one of the most treacherous pathogens among those causing hospital-acquired pneumonia (HAP). A. baumannii possesses an adaptable physiology, seen not only in its antibiotic resistance and virulence phenotypes, but also in its metabolic versatility. In this study, we observed that A. baumannii undergoes global transcriptional changes in response to human pleural fluid (PF), a key host-derived environmental signal. Differential gene expression analyses combined with experimental approaches revealed changes in A. baumannii metabolism, affecting cytotoxicity, persistence, bacterial killing and chemotaxis. Over 55% of the differentially expressed transcriptomic genes corresponded to metabolic processes, including the up regulation of glutamate, short chain fatty acid, and styrene metabolism. We observed an up regulation of the pyruvate dehydrogenase complex and found that pyruvate (PYR), in conjunction with PF, triggers an A. baumannii pathogenic behavior that adversely impacts human epithelial cell viability. Interestingly, PF also amplified A. baumannii cytotoxicity against murine macrophages, suggesting an immune evasion strategy implemented by A. baumannii. Moreover, we uncovered opposing metabolic strategies dependent on the degree of pathogenicity of the strains, where less pathogenic strains demonstrated greater utilization of PYR to promote persister formation in the presence of PF. Additionally, our transcriptomic analysis and growth studies of A. baumannii suggest the existence of an alternative phenylalanine (PA) catabolic route independent of the phenylacetic acid pathway, which converts PA to phenylpyruvate (PP) and shuttles intermediates into styrene metabolism. This alternative route promoted a neutrophil-evasive state, as PF-induced degradation of PP significantly reduced overall human neutrophil chemotaxis in ex vivo chemotactic assays. Taken together, these data highlights A. baumannii pathoadaptabililty in response to host signals and provide further insight into the role of bacterial metabolism in virulence traits, antibiotic persistence strategies, and host innate immune evasion.

Project description:Acinetobacter baumannii has emerged as one of the most problematic opportunist bacterial pathogen responsible for hospital-acquired and community infections worldwide. Besides its high capacities to acquire antibiotic resistance mechanisms, it also presents high adhesion abilities on inert and living surfaces leading to biofilm development, a lifestyle conferring an additional protection against various treatments, and allowing it to persist for long periods in various hospital niches. Due to their increasing resilience to antimicrobial treatments, A. baumannii biofilms are difficult to control and ultimately eradicate. Overcoming the significant challenges pose by A. baumannii require fundamental insights into mechanisms involved in the development of mature biofilm and thus, may help to develop novel strategies for biofilm prevention and control. To unravel critical determinants of this sessile lifestyle, we compared the proteome profiles of bacteria grown in planktonic stationary phase with those of two A. baumannii strains (ATCC 17978 and SDF), harboring specific features regarding biofilm formation, grown in mature solid-liquid (S-L) biofilm using a proteomic quantitative study. Of interest, among the 69 common proteins determinants accumulated in the two strains at the S-L interface, we sorted out the MacAB-TolC system. This tripartite efflux pump appears to play a role in A. baumannii biofilm formation as demonstrated by using ΔmacAB-tolC deletion mutant. Complementary approaches allowed us to get an overview of the impact of macAB-tolC deletion in A. baumannii physiology. Indeed, this efflux pump appeared to be involved in the envelope stress response occurring in mature biofilm and contributes to maintain WT membrane rigidity as well as tolerance to high osmolarity conditions. In addition, this system is probably involved in the maintenance of iron and sulfur homeostasis. MacAB-TolC might help this pathogen facing and adapting to biofilm architecture which is heterogeneous in space and time, especially in mature biofilm. Increasing our knowledge of A. baumannii biofilm formation will undoubtedly help us develop new therapeutic strategies to tackle this emerging threat to human health.

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