Emergence of ciprofloxacin- and tigecycline-resistant extended-spectrum β-lactamase (ESBL)-producing Salmonella enterica serovar Kentucky ST198 from horse, China.

OBJECTIVES

Salmonella enterica serovar Kentucky ST198 has been increasingly reported in diverse sources worldwide, emerging as a globally epidemic clone. In this study, we aim to characterise the first isolated S. Kentucky ST198 strain from a horse in China.

METHODS

Twelve faecal samples were collected from horses at a farm in Shihezi, Xinjiang Province, China, and investigated for the presence of Salmonella. The minimum inhibitory concentrations of 15 antimicrobial agents were determined using the broth microdilution method. The whole genome of Sal140 was sequenced using the Illumina Hiseq platform and assembled into contigs with SPAdes 3.10.0. Phylogenetic analysis was performed using Parsnp based on core-genome single-nucleotide polymorphisms.

RESULTS

A single S. Kentucky strain, designated Sal140, was isolated. This strain carried 15 antimicrobial resistance genes and exhibited resistance to ampicillin, ceftazidime, cefuroxime, cefotaxime, gentamicin, streptomycin, tetracycline, tigecycline, florfenicol, nalidixic acid, ciprofloxacin, azithromycin, and sulfamethoxazole/trimethoprim. Co-resistance to ciprofloxacin and third-generation cephalosporins was attributed to mutations in gyrA (S83F and D87G) and parC (T57S and S80I), and the production of CTX-M-55, respectively. Phylogenetic analysis revealed that Sal140 clustered within the subclade ST198.2-2, showing close genetic similarity (15-24 SNPs) to isolates from a patient and chicken meat in other regions of China, suggesting a potential epidemiological link among these S. Kentucky ST198 isolates from different sources.

CONCLUSIONS

In conclusion, the emergence of extensively drug-resistant (XDR) S. Kentucky ST198 in a horse is concerning. Continuous surveillance of this particular clone in horses is strongly recommended.