An Emerging Clone (ST457) of Acinetobacter baumannii Clonal Complex 92 With Enhanced Virulence and Increasing Endemicity in South China.

Background: The global dissemination of carbapenem-resistant Acinetobacter baumannii clonal complex (CC) 92 has become an urgent public health concern.
Methods: A. baumannii isolates were collected in 5 tertiary hospitals in south China during 2012-2015, and their clinical data were obtained. The clinical characterization was studied by statistical analysis. Whole-genome sequencing and a Galleria mellonella infection model were used to investigate the genetic characterization and pathogenicity of isolates, respectively.
Results: Sequence type (ST)457, following ST195, become the second-most prevalent clone in our collection. Patients infected by ST457 had significantly higher 7-day mortality rates (44.4% vs 14.3%; P = .01) and proportions of 7-day deaths (70.6% vs 26.7%; P = .01) than those infected by the other STs of CC92, except for ST195 and ST208. Consistently, the day of death after culture was significantly sooner in patients infected with ST457 than those with the non-ST195/208 members of CC92 (8.71 ± 15.27 vs 25.20 ± 6.51; P = .02). This is accordant with results that ST457 had enhanced virulence with a high mortality rate through use of the G. mellonella larvae infection model. Genomic analysis suggests that ST457 evolved distinctly from the other CC92 members mainly via recombinations. This clone exclusively shared a few virulence factors with the hypervirulence strain LAC-4, including a capsule biosynthesis locus (KL49) that is supposed to be important for the hypervirulence in LAC-4.
Conclusions: The rising trends in prevalence and enhanced virulence of ST457 highlight the urgent need for tailored surveillance to control the further dissemination of this clone.