Epidemiology and genetic characterization of tet(X4)-positive Klebsiella pneumoniae and Klebsiella quasipneumoniae isolated from raw meat in Chengdu City, China

The co-occurrence of tet(X4) and tmexCD2-toprJ2 mediated tigecycline resistance in Raoultella ornithinolytica

OBJECTIVES

This study aimed to characterize the co-occurrence of the tigecycline resistance determinants tet(X4) and tmexCD2-toprJ2 in a Raoultella ornithinolytica isolate collected from a pig rectal swab at the slaughterhouse.

METHODS

The R. ornithinolytica isolate WS60 was subjected to antimicrobial susceptibility testing. Whole-genome sequencing (WGS) was performed to analyze the genetic features of the plasmids carrying tet(X4) and tmexCD2-toprJ2. Additionally, a conjugation assay was conducted to evaluate the transferability of these plasmids, followed by a 15-day stability test to assess the persistence of the two resistance determinants.

RESULTS

R. ornithinolytica WS60 exhibited high-level tigecycline resistance, with a minimum inhibitory concentration (MIC) of 32 μg/mL, and was also resistant to ampicillin, ampicillin-sulbactam, chloramphenicol, tetracycline, sulfamethoxazole-trimethoprim, florfenicol, and streptomycin. WGS analysis revealed that WS60 harbored three plasmids, including a 384,249-bp tmexCD2-toprJ2-carrying IncQ plasmid (pWS60-1) and a 78,159-bp tet(X4)-carrying IncFII plasmid (pWS60-2). Interestingly, pWS60-2 was identical to several plasmids found in Klebsiella spp. isolated from animals, animal-derived food, and humans. Moreover, pWS60-2 was successfully transferred to Klebsiella spp. via conjugation, whereas pWS60-1 failed to transfer. Notably, no significant fitness cost was observed in the transconjugants carrying pWS60-2. Additionally, a 15-day stability assay demonstrated that both resistance determinants were stably maintained in the bacterial population without significant loss, underscoring their persistence over time.

CONCLUSIONS

This is the first report of the co-occurrence of tet(X4) and tmexCD2-toprJ2 in R. ornithinolytica. Enhanced surveillance in slaughterhouses, along with targeted interventions, should be implemented to mitigate the potential spread of mobile tigecycline resistance throughout the food production chain.

Genomic analyses reveal presence of extensively drug-resistant Salmonella enterica serovars isolated from clinical samples in Guizhou province, China, 2019-2023

Background

The emergence of extensively drug-resistant (XDR) Salmonella in humans poses a significant public health and therapeutic challenge. However, limited data are available on XDR Salmonella isolates from Guizhou province, China. This study aimed to investigate the molecular epidemiology and resistance patterns of XDR Salmonella isolates from clinical samples in this region.

Methods

A total of 931 Salmonella isolates were screened for XDR isolates through antimicrobial susceptibility testing. These XDR isolates were subjected to whole-genome sequencing (WGS) and bioinformatic analysis to further systematically investigating the molecular epidemiology and resistance patterns of XDR Salmonella isolates.

Results

Between 2019 and 2023, 931 Salmonella isolates were collected from clinical samples in Guizhou. Of these isolates, 51 (5.5%) were identified as XDR and classified into 16 serovars. Among the serovars, 15 corresponded to a specific sequence type, except for S. Typhimurium serovars. The predominant serovars, S. 1,4,[5],12:i:-, S. Enteritidis, and S. Kentucky, were divided into ST34, ST11, and ST198, respectively. Genomic analysis showed that all XDR isolates harbored at least eight antimicrobial resistance genes (ARGs) and multidrug efflux pumps. Highly prevalent point mutations in gyrA (D87 and S83) and parC (S80I) were detected, along with eight plasmid-mediated quinolone resistance (PMQR) genes. The qnrS1 gene was the most common (43.1%), followed by oqxA, aac-(6')-lb-cr variant, qnrB4, qnrS2, qnrA1, qepA2, and oqxB. The predominant β-lactamase gene was blaTEM-1 (54.9%), and blaCTX-M-55 (35.3%) was the most prevalent extended-spectrum β-lactamase subtype. Notably, blaNDM-1 gene was identified for the first time in Salmonella from Guizhou, and one S. 1,4,[5],12:i:- isolate contained the mcr-1.1 gene. ARGs profiles varied by serovars, with S. 1,4,[5],12:i:- isolates carrying the highest number. Ten plasmid types were identified, predominantly IncHI2/IncHI2A (47.5%). Key resistance genes such as tetA, PMQR, blaCTX-M , mcr-1.1, and blaNDM-1 were located on IncHI2/IncHI2A plasmids. Notably, 75.0% of the conjugative plasmids belonged to IncHI2/IncHI2A, indicating that horizontal gene transfer through conjugation facilitates ARGs dissemination. Core genome multilocus sequence typing (cgMLST) analysis revealed significant genetic diversity, with 39 core genome sequence types (cgSTs) identified and no evidence of outbreaks.

Conclusion

The rising prevalence of XDR Salmonella in Guizhou province is concerning. Initial whole-genome sequencing (WGS) data provide critical insights for understanding and controlling XDR Salmonella infections, aiding public health officials in identifying emerging threats and trends.