Tolerance mechanisms and molecular epidemiology of reduced susceptibility to chlorhexidine digluconate in different species of the Acinetobacter baumannii complex.

Abstract

The objective of this study was to compare chlorhexidine digluconate and other antibiotics susceptibility of 4 species in Acinetobacter baumannii complex, and further investigate the CHG tolerance mechanisms and molecular epidemic characteristics. Of 889 A. baumannii complex isolates, A. baumannii, A. nosocomialis, A. pittii, and A. seifertii accounted for 84.2%, 10.9%, 3.4%, and 1.5%. A. baumannii was generally resistant to all tested antibiotics while other three species were commonly more susceptible. 92.1% (313/340) CHG-tolerant A. baumannii, 19.6% (19/97) CHG-tolerant A. nosocomialis, 3.3% (1/30) CHG-tolerant A. pittii and 15.4% (2/13) CHG-tolerant A. seifertii were identified. Furthermore, compared to A. baumannii ATCC 19606, upregulated expression was found in qacEΔ1, FabI and efflux pump encoding genes in CHG-tolerant A. baumannii, but the expression level of oprD was reduced. Additionally, only the expression level of FabI was increased in the CHG- tolerant A. nosocomialis, and the expression level of adeG was increased in the CHG- tolerant A. pittii and A. seifertii. Furthermore, CHG-tolerant A. baumannii may have a relatively high clonal correlation, the predominant ST of which was ST208 (90%, 36/40).It is rather necessary to identify specific species members among the A. baumannii complex for clinical treatment options and antibiotics resistance monitoring.