Molecular characterization of Cephalosporin-resistant Salmonella Enteritidis ST11 isolates carrying blaCTX-M from children with diarrhea

Authors: LI, CONGCONG - Shanghai Jiaotong University; ZHANG, ZENGFENG - Shanghai Jiaotong University; XU, XUEBIN - Shanghai Jiaotong University; HE, SHOUKUI - Shanghai Jiaotong University; ZHAO, XIAODONG - Shanghai Jiaotong University; YAN, CUI - Shanghai Jiaotong University; XIUJUAN, ZHOU - Shanghai Jiaotong University; SHI, CHUNLEI - Shanghai Jiaotong University; Liu, Yanhong; ZHOU, MIN - Wuhan University; SHI, XIANMING - Shanghai Jiaotong University

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2021
Publication Date: 2/2/2021
Citation: Li, C., Zhang, Z., Xu, X., He, S., Zhao, X., Yan, C., Xiujuan, Z., Shi, C., Liu, Y., Zhou, M., Shi, X. 2021. Molecular characterization of Cephalosporin-resistant Salmonella Enteritidis ST11 isolates carrying blaCTX-M from children with diarrhea. Foodborne Pathogens and Disease. https://doi.org/10.1089/fpd.2020.2878.
DOI: https://doi.org/10.1089/fpd.2020.2878

Interpretive Summary: Salmonella is a major bacterial foodborne pathogen that causes a disease called salmonellosis. Severe Salmonella infections are treated with antibiotics; however, Salmonella strains are becoming increasingly more resistant to antibiotics in China and other countries worldwide. To mitigate the development of resistance in this pathogen, it is important to identify and characterize Salmonella strains that acquire antibiotic resistance. Our research showed that 15/162 Salmonella strains isolated from children in China from 2007 to 2017 were resistant to antibiotics known as cephalosporins. Most of the genes conferring resistance to cephalosporins were located on a large plasmid (small circular DNA molecule that replicates independent of the bacterial chromosome) found in the bacteria. The plasmid contained a large multidrug resistance region of DNA that carried a number of antibiotic resistance genes, and experiments demonstrated that resistance genes could be transferred to other bacteria. These findings emphasize the importance of surveillance for the prevalence and transmission of the antibiotic resistance genes in Salmonella to better understand the potential threat to public health and to develop control strategies.

Technical Abstract: Salmonella Enteritidis (S. Enteritidis) is an important foodborne pathogen with high prevalence of resistance to cephalosporins, imposing a serious threat to public health. Therefore, a total of 162 S. Enteritidis isolates collected from child patients in China from 2007 to 2017 were characterized for their resistance to cephalosporins and investigated the transmission characteristics of cephalosporin resistance gene. We found that 15 (9.26%) isolates were all resistant to cefalotin (MIC = 512 µg/mL), ceftazidime (MIC 16 to 128 µg/mL), ceftriaxone (MIC 64 to = 512 µg/mL), ceftiofur (MIC 64 to 256 µg/mL) and cefotaxime (MIC 64 to = 512 µg/mL) with the possession of cephalosporin resistance genes blaCTX-M-55 (n=13), blaCTX-M-101 (n=1) and blaCTX-M-153 (n=1). Molecular typing further revealed that these 15 isolates belonged to sequence type ST11 and shared close PFGE patterns, suggesting the possibility of clonal spread in S. Enteritidis interspecies. Furthermore, conjugation experiments were successfully performed in 13 of 15 isolates, and blaCTX-M-55 was present on conjugative plasmids with sizes ranging from 78.2 to 173.4 kb. Compared with recipient E. coli C600, transconjugants conferred elevated MICs for cephalosporins ranging from 2- to 2133-fold. The genetic structure surrounding of blaCTX-M-55 gene in transconjugants were 'ISEcp1-blaCTX-M-55-orf477 (n=8) and ISEcp1-blaCTX-M-55-orf477 (n=3), respectively. Taken together, blaCTX-M on the plasmids might contributed to cephalosporin resistance in S. Enteritidis, and conjugative transfer of blaCTX-M-55 might contribute to the spread of cephalosporin resistance in S. Enteritidis. Hence, effective mitigation measurements are needed to reduce the threat caused by cephalosporin-resistant S. Enteritidis to public health.