Human Pleural Fluid Elicits Pyruvate and Phenylalanine Metabolism in Acinetobacter baumannii to Enhance Cytotoxicity and Immune Evasion.

Nyah Rodman,Amber L Myers,Caitlin M Harris,Jennifer S Fernandez,Sammie Fung,Jasmine Martinez,Anthony M Mendoza,Christine Liu,Emily Dang,Rodrigo Sieira,Veronica Jimenez,Maria Soledad Ramirez,Jun Nakanouchi,Catherine A Brennan,Robert A Bonomo,Nikolas Nikolaidis

doi:10.3389/fmicb.2019.01581

Abstract

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 1,220 genes representing 55% of the differentially expressed transcriptomic data corresponded to metabolic processes, including the upregulation of glutamate, short chain fatty acid, and styrene metabolism. We observed an upregulation by 1.83- and 2.61-fold of the pyruvate dehydrogenase complex subunits E3 and E2, respectively. We also 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 highlight 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.

Highlights

IntroductionAcinetobacter baumannii is a notorious nosocomial pathogen with mortality rates among patients in intensive care units reported between 21.6 and 67% (Falagas et al, 2006; Peleg et al, 2008; Roca et al, 2012; Park et al, 2013; Inchai et al, 2015; Xiao et al, 2017)
In the presence of mucin, a glycoprotein secreted by lung epithelial cells, virulence features associated with the paa operon, as well benzoate metabolism, amino acid and lipid catabolism, electron transport activity, and peptide transport are upregulated (Ohneck et al, 2018)
HSA, a component of PF, was previously reported to promote expression of arginine metabolism and succinyl-CoA production genes, to which the latter was linked to polypetide biosynthesis, a metabolite that can confer a competitive advantage during pathogenesis (Allen and Gulick, 2014; Quinn et al, 2018c)

Summary

Introduction

Acinetobacter baumannii is a notorious nosocomial pathogen with mortality rates among patients in intensive care units reported between 21.6 and 67% (Falagas et al, 2006; Peleg et al, 2008; Roca et al, 2012; Park et al, 2013; Inchai et al, 2015; Xiao et al, 2017). A. baumannii is responsible for a high number of health-care-associated cases of pneumonia, bacteremia, and urinary, skin, or surgical-derived infections (Peleg et al, 2008; Roca et al, 2012; Wong et al, 2017) This Gram-negative bacterium has garnered considerable clinical significance as a result of its intrinsic antibiotic resistance mechanisms, innate ability to persist for long periods upon desiccation and starvation, and capability to acquire foreign resistance determinants from the surrounding environment (Jawad et al, 1998; Peleg et al, 2008; Adams et al, 2010; Sahl et al, 2013; Chapartegui-Gonzalez et al, 2018). Cytolytic activity and immunoevasive mechanisms of A. baumannii have been linked to metal acquisition and phenylacetic acid (PAA) metabolism (Bhuiyan et al, 2016; Fiester et al, 2016)

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