Genomic and phenotypic characterisation of antimicrobial resistance in carbapenem-resistant Acinetobacter baumannii hyperendemic clones CC1, CC15, CC79 and CC25.

Dissemination of carbapenem-resistant Acinetobacter baumannii (CRAB) is mainly driven by the spread of clonal lineages. High frequencies of CRAB are reported in South America, and clonal complexes CC1, CC15, CC79 and CC25 are predominant. A total of 79 non-redundant CRAB recovered from 26 Brazilian hospitals were selected for antimicrobial susceptibility testing by microdilution and whole-genome sequencing (WGS). Multilocus sequence typing (MLST), acquired antimicrobial resistance genes and phylogeny based on high-quality SNPs were extracted from WGS data. XDR (86.1%), MDR (12.7%) and one PDR isolate from CC15 (1.3%) were identified. Colistin resistance was more frequent in CC25 isolates (P < 0.01). Prevalence of CC79 (n = 22; 27.8%) CC1 (n = 21; 26.6%), CC15 (n = 21; 26.6%) and CC25 (n = 12; 15.2%) was observed. Regarding carbapenem-hydrolysing class D β-lactamases (CHDLs), bla was frequently detected in CC1, CC15 and CC25 isolates, whereas bla was the most frequent CHDL in CC79 isolates [n = 12/22 (54.5%); P < 0.01]. High-quality SNP analysis correlated well with sequence type and revealed that CRAB clones are highly conversed and present some clone-specific resistance determinants. This study provides essential information to understand the antimicrobial resistance patterns of CRAB in Brazilian hospitals, where hyperendemic XDR-CRAB clones are disseminated. Phenotypic and genomic analysis of CRAB recovered from Brazilian hospitals revealed the predominance of XDR phenotype in the majority of international clonal complex CC79, CC1, CC15 and CC25. Dissemination of specific CRAB lineages in Brazil is suggested to be driven by their resistance determinants under antimicrobial selective pressure.