ABSTRACT
The purpose of this study was to characterize extensively drug-resistant Salmonella enterica serovar Kentucky sequence type 198 (ST198) isolates from chicken meat products. Ten S. Kentucky strains obtained from chicken meat products in Xuancheng, China, carried 12 to 17 resistance genes, such as blaCTX-M-55, rmtB, tet(A), floR, and fosA3, combined with mutations within gyrA (S83F and D87N) and parC (S80I), resulting in resistance to numerous antimicrobial agents, including the clinically important antibiotics cephalosporin, ciprofloxacin, tigecycline, and fosfomycin. These S. Kentucky isolates shared a close phylogenetic relationship (21 to 36 single-nucleotide polymorphisms [SNPs]) and showed close genetic relatedness to two human clinical isolates from China. Three S. Kentucky strains were subjected to whole-genome sequencing using Pacific Biosciences (PacBio) single-molecule real-time (SMRT) technology. All antimicrobial resistance genes were located on their chromosomes and clustered in one multiresistance region (MRR) and Salmonella genomic island (SGI) SGI1-K. The MRRs in three S. Kentucky strains were bounded by IS26 at both ends and were inserted downstream of the bcfABCDEFG cluster with 8-bp direct repeats. The MRRs were related to those of IncHI2 plasmids but differed by insertions, deletions, and rearrangements of multiple segments involving resistance genes and plasmid backbones. This finding suggests that the MRR fragment possibly originates from IncHI2 plasmids. Four SGI1-K variants with slight differences were identified in 10 S. Kentucky strains. Mobile elements, particularly IS26, play an essential role in forming distinct MRRs and SGI1-K structures. In conclusion, the emergence of extensively drug-resistant S. Kentucky ST198 strains containing numerous chromosomally located resistance genes is alarming and needs continued surveillance. IMPORTANCE Salmonella spp. are important foodborne pathogens, and multidrug-resistant (MDR) Salmonella strains have become a serious threat to clinical therapy. MDR S. Kentucky ST198 strains have been increasingly reported from various sources and have become a global risk. In this study, we described extensively drug-resistant S. Kentucky ST198 strains from chicken meat products from a city in China. Numerous resistance genes are clustered in the chromosomes of S. Kentucky ST198 strains, possibly acquired with the help of mobile elements. This would facilitate the spread of numerous resistance genes as intrinsic chromosomal genes within this global epidemic clone, with the potential to capture more resistance genes. The emergence and dissemination of extensively drug-resistant S. Kentucky ST198 pose a severe clinical and public health threat; therefore, continuous surveillance is warranted.
ABSTRACT
This study aimed to investigate the prevalence and diversity of extended-spectrum ß-lactamases (ESBL)-producing Escherichia coli isolates from healthy individuals in a community and to elucidate their dissemination mechanism. Cefotaxime-resistant E. coli were isolated from 95 samples of healthy persons from one community in Yangzhou, China, and were tested for minimal inhibitory concentrations of 14 antimicrobial agents. The isolates were subjected to whole genome sequencing by Illumina Hiseq or PacBio single-molecule real-time sequencing. A total of 30 cefotaxime-resistant E. coli isolates were obtained, carrying bla CTX-M (n=29) or bla DHA (n=1), of which the bla CTX-M-55 (n=19) was the most predominant genotype. One novel bla CTX-M variant bla CTX-M-252 was identified. Thirteen CTX-M-55-producing E. coli isolates belonged to ST8369 from nasal (n=12) or faecal (n=1) samples shared the identical cgMLST type, resistance profiles, resistance genes, plasmid replicons, and a 5,053-bp bla CTX-M-55 structure ΔIS26-ΔISEcp1-bla CTX-M-55-Δorf477-ΔTn2. The bla CTX-M-55 gene was located on IncHI2/ST3 plasmid in E. coli ST8369. The lengths of bla CTX-M/bla DHA-carrying contigs in the remaining 17 E. coli strains ranged from 1,663 to 382,836 bp, located on chromosome (n=4) or plasmids (n=5); the location of the other eight contigs could not be determined due to incomplete assembly. The bla CTX-M was associated with ISEcp1 as previously reported. Nasal colonization of CTX-M-55-producing ST8369 E. coli strains has occurred among healthy individuals in one community. There is a potential risk of antimicrobial resistance dissemination between humans within one community through close contact or environment via aerosols or dust. Therefore, surveillance of nasal carriage of bla CTX-M in communities is warranted to further monitor the spread of the antimicrobial resistance genes in China.
