The population structure of Acinetobacter baumannii isolated from animals: an emerging zoonotic threat.

To investigate the population structure of Acinetobacter baumannii in animals and the transmission pattern between humans and animals, we conducted a molecular epidemiological study by supplementing the data from poultry combined with data from 509 animal isolates and 2,218 human isolates in the NCBI GenBank database. Antibiotic susceptibility testing and genomic analysis showed that A. baumannii isolated from the brains of dead poultry embryos was universally sensitive to 19 antibiotics and genetically diverse. The pathogen has been isolated from 33 animal species from 17 countries worldwide. According to the established international clones (ICs), IC2 (n = 2), IC5 (n = 9), IC7 (n = 6), and IC8 (n = 10) were the main clonal lineages among the 170 sequence types (STs). Particularly, the ST25 lineage isolates in IC7, which were detected in nine animal species, mainly companion animals such as cats, dogs, and horses. In addition, 115 STs belonged to unique clones. A. baumannii isolated from animals can be divided into two groups: a high antimicrobial resistance (AMR) group dominated by hosts such as horses, cats, and dogs and a low AMR group dominated by hosts such as livestock, poultry, and wildlife. In the low AMR group, the isolates carried fewer AMR and virulence genes than human isolates in the same region. Compared with the low AMR group, isolates in the high AMR group shared more STs with human isolates in the same region. In conclusion, our study suggests that A. baumannii has a higher potential of intertransmission between companion animals and humans compared to livestock, poultry, and wildlife.IMPORTANCEThe population structure of A. baumannii in animals has been systematically and comprehensively revealed by molecular epidemiological studies of A. baumannii isolated from animals worldwide. A. baumannii isolated from animals can be divided into two groups, a high antimicrobial resistance (AMR) group dominated by hosts such as horses, cats, and dogs and a low AMR group dominated by hosts such as livestock, poultry, and wildlife. The integration of the distribution of AMR and virulence genes, the phylogenetic tree, and the multi-locus sequence typing results suggests a higher potential of intertransmission between companion animals and humans. This elevated potential may be related to the close contact of companion animals with humans.