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In Vivo-Validated Essential Genes Identified in Acinetobacter baumannii by Using Human Ascites Overlap Poorly with Essential Genes Detected on Laboratory Media

Umland, Timothy C., Schultz, L. Wayne, MacDonald, Ulrike, Beanan, Janet M., Olson, Ruth, Russo, Thomas A.
mBio 2012 v.3 no.4 pp. e00113-12
Acinetobacter baumannii, DNA, Enterobacter, Escherichia coli, Gram-negative bacteria, Klebsiella pneumoniae, Pseudomonas aeruginosa, RNA, abscess, anti-infective agents, ascites, culture media, databases, drugs, essential genes, humans, models, mutants, pathogens, protein transport, rats, screening
A critical feature of a potential antimicrobial target is the characteristic of being essential for growth and survival during host infection. For bacteria, genome-wide essentiality screens are usually performed on rich laboratory media. This study addressed whether genes detected in that manner were optimal for the identification of antimicrobial targets since the in vivo milieu is fundamentally different. Mutant derivatives of a clinical isolate of Acinetobacter baumannii were screened for growth on human ascites, an ex vivo medium that reflects the infection environment. A subset of 34 mutants with unique gene disruptions that demonstrated little to no growth on ascites underwent evaluation in a rat subcutaneous abscess model, establishing 18 (53%) of these genes as in vivo essential. The putative gene products all had annotated biological functions, represented unrecognized or underexploited antimicrobial targets, and could be grouped into five functional categories: metabolic, two-component signaling systems, DNA/RNA synthesis and regulation, protein transport, and structural. These A. baumannii in vivo essential genes overlapped poorly with the sets of essential genes from other Gram-negative bacteria catalogued in the Database of Essential Genes (DEG), including those of Acinetobacter baylyi , a closely related species. However, this finding was not due to the absence of orthologs. None of the 18 in vivo essential genes identified in this study, or their putative gene products, were targets of FDA-approved drugs or drugs in the developmental pipeline, indicating that a significant portion of the available target space within pathogenic Gram-negative bacteria is currently neglected.