Genomic characterization of the virulence-associated pyomelanin biosynthetic pathway in pigment-producer strains from the pandemic Acinetobacter baumannii IC-5

Abstract

BACKGROUNDAcinetobacter baumannii outbreaks have been associated with pandemic International Clones (ICs), however the virulence factors involved with their pathogenicity are sparsely understood. OBJECTIVESThis study aimed to characterize the reddish-brown pigment produced by A. baumannii strains, and to determine its biosynthetic pathway by genomic approaches. METHODSPigment characterization was conducted by phenotypic tests in different growth conditions. The clonal relationship among A. baumannii was obtained by PFGE and MLST and antimicrobial susceptibility test was performed by Disc-Diffusion method. The genome of one representative strain was obtained for characterization of genes involved with pigment production. FINDINGSThe virulence-associated pyomelanin was the pigment produced by A. baumannii. These strains were extensively drug resistant and belonged to the IC-5/ST79. Genomic approaches revealed that the pyomelanin biosynthetic pathway in A. baumannii presented a particular architecture concerning the peripheral (tyrB, phhB and hpd) and central (hmgB, hmgC and hmgR) metabolic pathway genes. The identification of a distant HmgA homologue, probably without dioxygenase activity, could explain pyomelanin production. Virulence determinants involved with adherence (csuA/BABCDE and a T5bSS-carrying genomic island), and iron uptake (basABCDEFGHIJ, bauABCDEF and barAB) were also characterized. MAIN CLONCLUSIONThe pyomelanin production together with other virulence determinants could play a role in A. baumannii pathogenicity.