Abstract
Background Acinetobacter baumannii is an emerging bacterial pathogen that causes a broad array of infections, particularly in hospitalized patients. Many studies have focused on the epidemiology and antibiotic resistance of A. baumannii, but little is currently known with respect to its virulence potential.Methodology/Principal FindingsThe aim of this work was to analyze a number of virulence-related traits of four A. baumannii strains of different origin and clinical impact for which complete genome sequences were available, in order to tentatively identify novel determinants of A. baumannii pathogenicity. Clinical strains showed comparable virulence in the Galleria mellonella model of infection, irrespective of their status as outbreak or sporadic strains, whereas a non-human isolate was avirulent. A combined approach of genomic and phenotypic analyses led to the identification of several virulence factors, including exoproducts with hemolytic, phospholipase, protease and iron-chelating activities, as well as a number of multifactorial phenotypes, such as biofilm formation, surface motility and stress resistance, which were differentially expressed and could play a role in A. baumannii pathogenicity.Conclusion/SignificanceThis work provides evidence of the multifactorial nature of A. baumannii virulence. While A. baumannii clinical isolates could represent a selected population of strains adapted to infect the human host, subpopulations of highly genotypically and phenotypically diverse A. baumannii strains may exist outside the hospital environment, whose relevance and distribution deserve further investigation.
Highlights
IntroductionAcinetobacter baumannii is an emerging human pathogen which causes a broad array of infections (e.g. pneumonia, urinary tract, bloodstream and skin infections) that account for about 10% of all nosocomial infections [1,2,3]
Acinetobacter baumannii is an emerging human pathogen which causes a broad array of infections that account for about 10% of all nosocomial infections [1,2,3]
No significant differences in virulence were observed between the epidemic strains AYE and ACICU and the non-epidemic strain ATCC 17978 (P.0.05), all three of which showed similar Lethal dose 50% (LD50) values
Summary
Acinetobacter baumannii is an emerging human pathogen which causes a broad array of infections (e.g. pneumonia, urinary tract, bloodstream and skin infections) that account for about 10% of all nosocomial infections [1,2,3]. Since the 1980s, three main epidemic A. baumannii lineages, hereafter referred to as clonal complexes I, II and III (CC1, CC2 and CC3, respectively) have emerged and spread internationally throughout many geographical areas [4] Both multi-locus sequence typing and comparative genomics analysis revealed that isolates belonging to the same CC are highly homogenous, suggestive of a recent clonal expansion [4,5]. The molecular and genetic basis of A. baumannii virulence remains poorly understood, and only a few determinants have been demonstrated to be important for A. baumannii virulence in vivo One of these is OmpA, an outer membrane protein which adheres to and is taken up by epithelial cells, where it can induce apoptosis [9]. Many studies have focused on the epidemiology and antibiotic resistance of A. baumannii, but little is currently known with respect to its virulence potential
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