Molecular characterization of Escherichia coli producing a novel Shiga toxin 2k subtype detected in one district of Beijing

  Objective  To understand the etiological and molecular characteristics of two strains of non-O157 Escherichia coli producing Shiga toxin (STEC), which were isolated for the first time in the surveillance for diarrhea in one district of Beijing from 2013 to 2021.

  Methods  The stool samples from diarrhea patients were screened for enteropathogenic bacteria and viruses by using real-time PCR. The stx-positive samples were selected for isolation. After biochemical identification, the STEC strains were investigate by serum agglutination, micro-broth dilution assays and whole genome sequencing. Based on whole genomic sequences, serotypes, multi-locus sequence types, drug resistance genes, and stx subtypes were predicted, and the phylogenetic tree were constructed.

  Results  In 2021, the stool samples from two middle-aged women with diarrhea were detected to be positive for stx gene, however, the suspected exposed food could not be identified. Two STEC strains carrying stx1a and stx2k were isolated respectively. The Stx1a-STEC was identified as serotype O45:H6, ST101, with a drug-sensitive phenotype of ampicillin+tetracycline+cefotaxime sodium+cefazolin+gentamicin+compound sulfamethoxazole, which carried resistance genes aac(3)-Ⅱd, tetA, lnu(F), aadA22, aph(6)-Id, sul3, qnrS1, ant(3'')-Ia, bla_CTX-M-55. The specimen was also rotavirus positive. The Stx2k-STEC was identified as serotype O150:H8, ST906, it was sensitive to all the tested 15 antibiotics, no resistance gene was detected. Phylogenetic analysis revealed high genetic diversity between the two isolates and STEC reference strains.

  Conclusion  Infections caused by STEC existed in this district of Beijing, and the novel Shiga toxin 2k was detected. The surveillance for STEC should be enhanced.