Increased capsule thickness and hyper-motility are traits of carbapenem-resistant Acinetobacter baumannii ST3 strains causing fulminant infection
Abstract Acinetobacter baumannii is a successful nosocomial pathogen, causing severe, life-threatening infections in hospitalized patients, including pneumonia and bloodstream infections. The spread of CRAB (carbapenem-resistance Acinetobacter baumannii) strains is a major world-health threat. The successful spread of CRAB is mostly due to it's highly plasticity genome. Although some virulence factors associated with CRAB have been uncovered, many mechanisms contributing to its success are not fully understood. Here we describe strains of CRAB that were isolated from fulminant cases in two hospitals in Israel. These isolates show a rare, hyper mucoid (HM) phenotype and were investigated using phenotypic assays, comparative genomics and in vivo Galleria Mellonella model. The three isolates belonged to the ST3 international clonal type and closely related to each-other as shown by Fourier Transform Infrared Spectroscopy (FTIR) and phylogenetic analyses. These isolates possessed thickened capsules and dense filamentous extracellular polysaccharides (EPS) matrix as shown by transmission electron microscopy (TEM), and overexpress capsule polysaccharide synthesis pathway-related wzc gene. The HM isolates possessed a unique combination of virulence genes involved in iron metabolism, protein secretion, adherence and membrane glycosylation. HM strains were more virulent than control strains in two G. mellonella infection models. In conclusion, our findings demonstrated several virulence factors, all present in three CRAB isolates with rare hyper mucoid phenotypes.