Abstract

The multidrug resistant Acinetobacter baumannii is one of the emerging health threatening -bacteria globally. Phase variation in this bacterium showed to play a role in switching between different phenotypes that displayed different capacities to resist adverse conditions. In this study, computer based analysis was applied to characterize the Simple Sequence Repeats (SSRs) in 32 genomes of A. bumannii, and to evaluate their potential mediating of phase variation of certain genes. SSRs were screened in terms of their types, periodic length, motifs and location within coding or intergenic regions. A total of 2277 SSR loci were detected in the total genomes analyzed, dominated by poly A/T tracts which represented 57.1 % of the whole SSRs detected. Excluding the tracts that not affecting gene expression, the total number of candidate phase variable (PV) genes identified were 1860 genes, ranged from 49 to 79 genes per genome. The majority of these genes have their SSRs within coding sequences. The genes clustered into 402 distinct homologous groups, and 42 of them are found in more than 50 % of the total isolates analyzed. Only 27 genes showed interstrain variability in their SSR numbers, and only five of them switched between different expression states (On/ Off) over genomes. In general, the detected SSRs are mainly short, and have a limited role in variation of surface antigens, but it potentially mediates phase variation in genes that are supposed to participate in drug resistance, reflecting their possible importance in regulating such ability in A. baumannii