Genome comparison of Acinetobacter baumannii: evaluation of drug resistance, adherence, haemolysis and other potential virulence factors

Abstract number: O444

Imperi F., Iacono M., Antunes L., Villa L., Visca P., De Bellis G., Cassone A., Carattoli A.

Objectives: despite the importance of Acinetobacter baumannii as emerging pathogen worldwide, studies on the mechanisms underlying its pathogenesis are lacking. Multidrug resistant strains are emerging throughout many geographic areas and two pan-epidemic European clones (I and II) have been documented, endowed with a broad range of antibiotic resistance. In this study, the genome sequences of the multidrug resistant A. baumannii ACICU (European clone II; Iacono et al. AAC 2008) and AYE (European clone I, Vallenet et al. PLOS One 2008) strains were compared with the genome of the antibiotic susceptible, not pathogenic SDF strain, and with that one of the reference ATCC17978 strain (Smith et al. Genes Dev 2007) with the aim of identifying genomic regions implied in pathogenesis and drug resistance.

Methods: protein similarities were searched by the BLASTp algorithm. Pathogenicity studies were performed using the Galleria mellonella model of infection. Haemolysis was evaluated on defibrinated horse blood.

Results: in this study, we used larvae of the insect G. mellonella (greater wax moth) as infection model to compare the virulence of the A. baumannii strains ATCC17978, AYE, ACICU and SDF. The 50% lethal dose (LD50) was comparable for AYE and ACICU, while it was ca. 10- and 100-fold higher when larvae were infected with ATCC17978 and SDF, respectively. Thus, the SDF genome was used as reference genome to identify functions acquired by pathogenic strains with a possible role in antibiotic resistance and pathogenicity. Sixty-two clusters, corresponding to almost 870 CDSs, were identified in the ACICU and AYE genomes (and partially in ATCC17978) that were absent in SDF. These clusters encode: (i) resistance genes and transporters plausibly involved in drug efflux (30 transporters of the MFS, DMT, ABC, RND, MOP and ACR3 families were unique of drug resistant strains and absent in the susceptible SDF strain); (ii) pili and fimbriae systems related to biofilm formation and motility; (iii) haemolysin- and haemagglutinin-related proteins differently distributed among the four genomes, (iv) iron uptake and other metabolic genes.

Conclusion: Genome comparison identified unique features of A. baumannii epidemic clones and provided novel insights into the genetic basis of multidrug resistance and pathogenesis in this species. This study may contribute to understand the concept of infection, invasiveness and colonisation in the emergent pathogen A. baumannii.

Session Details

Date: 16/05/2009
Time: 00:00-00:00
Session name: 19th European Congress of Clinical Microbiology and Infectious Diseases
Location: Helsinki, Finland, 16 - 19 May 2009
Presentation type:
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