The success of particular Acinetobacter baumannii clones: accumulating resistance and virulence inside a sugary shield.

BACKGROUND

In Portugal, carbapenem-resistant Acinetobacter baumannii (CRAB) has been associated with ST98, ST103 and ST208 (Oxford Scheme, Oxf) and a clone has usually been associated with a particular period of time. These clonal shifts were primarily explained by an increased antimicrobial resistance profile. Here we explore genomic and biochemical differences among these and more recent clones, which could further explain the diversity and evolution of this species.

METHODS

A total of 116 CRAB isolates (2010-15), together with representatives of a previously described CRAB collection (4 isolates, 2001-06) were characterized by attenuated total reflection Fourier transform infrared spectroscopy (FTIR-ATR) and MLST. Representatives of different FTIR-ATR/MLST clusters were selected for WGS (n = 13), which allowed the in silico extraction of resistance and virulence genes, capsule locus and SNP analysis.

RESULTS

A. baumannii clonal shifts of OXA-58-producing ST103Oxf (2001-04), OXA-40-producing ST98Oxf (2002-06), OXA-23-producing ST208Oxf (2006-10) and OXA-23-producing ST218Oxf (2010-15) were accompanied by an increase in AMR genes and virulence factors. FTIR-ATR clustering was congruent with sugar composition predicted from the capsular locus: a fucosamine cluster comprising ST98Oxf, ST103Oxf and a single ST218Oxf isolate; a pseudaminic acid cluster of ST208Oxf and ST1557Oxf isolates; and legionaminic acid, resembling the sialic acid from mammalian cells, in a cluster comprising ST218Oxf isolates. The whole-genome phylogenetic tree was congruent with MLST, with isolates presenting 5-28 938 SNPs. ST208Oxf and ST218Oxf presented ∼1900 SNPs while ST103Oxf and ST1557Oxf showed a greater number of SNPs (∼28 000).

CONCLUSIONS

Clonal shifts of CRAB were promoted, in our country, by consecutive virulence and AMR gene pool enlargement, together with features increasing pathogen-host adaptation. Worldwide dominance of ST218Oxf is supported by the combination of high AMR and virulence levels.