The K1 Capsular Polysaccharide of Acinetobacter baumannii Strain 307-0294 Is a Major Virulence Factor

Abstract

Acinetobacter baumannii is a pathogen of increasing medical importance with a propensity to be multidrug resistant, thereby making treatment challenging. Little is known of virulence traits in A. baumannii. To identify virulence factors and potential drug targets, random transposon (Tn) mutants derived from the A. baumannii strain AB307-0294 were screened to identify genes essential for growth in human ascites fluid in vitro, an inflammatory exudative fluid. These studies led to the identification of two genes that were predicted to be required for capsule polymerization and assembly. The first, ptk, encodes a putative protein tyrosine kinase (PTK), and the second, epsA, encodes a putative polysaccharide export outer membrane protein (EpsA). Monoclonal antibodies used in flow cytometric and Western analyses confirmed that these genes are required for a capsule-positive phenotype. A capsule-positive phenotype significantly optimized growth in human ascites fluid, survival in human serum, and survival in a rat soft tissue infection model. Importantly, the clearance of the capsule-minus mutants AB307.30 (ptk mutant, capsule minus) and AB307.45 (epsA mutant, capsule minus) was complete and durable. These data demonstrated that the K1 capsule from AB307-0294 was an important protectin. Further, these data suggested that conserved proteins, which contribute to the capsule-positive phenotype, are potential antivirulence drug targets. Therefore, the results from this study have important biologic and translational implications and, to the best of our knowledge, are the first to address the role of capsule in the pathogenesis of A. baumannii infection.

Diversity Within the O-linked Protein Glycosylation Systems of Acinetobacter Species

“…On all instruments the 5 most abundant precursor ions were selected and dynamic exclusion of 30 s enabled. MS resolution was set to 60,000 with an ACG target of 1 ϫ 10 6 , maximum fill time of 500 ms and a mass window of 600 to 2000 m/z. HCD fragmentation (normalized collision energy 40) was carried out with an ACG of 2 ϫ Glycopeptide Data Processing-The raw files were then processed within Proteome Discover version 1.3 (Thermo Scientific) to generate mgf files and searched using Sequest against a composite FASTA database of strain SDF, ATCC17978, and AYE (NCBI accession: NC_010400.1, NC_009085.1 and NC_010410.1 respectively, obtained from NCBI on 10/07/2012).…”

Acinetobacter baumannii: biology and drug resistance — role of carbapenemases

“…The active protection of the CPS enables A. baumannii to avoid bactericidal activity of the complement. The authors also suggested that the CPS protection against the effects of phagocytes or antimicrobial peptides requires further studies [26]. AbOmpA is considered to be one of the best-characterised A. baumannii virulence factors.…”

Insights into Acinetobacter baumannii pathogenicity

“…A pilot study assessing A. baumannii infection of bone in a rat model has also been performed (45). Virulence factors that have been identified using this approach include penicillinbinding protein 7/8 (20), a glycosyltransferase (LpsB) involved in LPS biosynthesis (23), and genes (ptk and epsA) important for capsule formation (22). Phospholipase D was shown to be important for growth in human serum and for epithelial cell invasion, but in the murine pneumonia model, similar bacterial burdens and histopathology were identified (24).…”