Abstract:【】 Objective To understand the characteristic and antibiotic resistance traits of Shiga toxin-producing Escherichia coli (STEC) derived from animal in Shandong province, providing a basis for the risk assessment and surveillance of STEC infection,Constructing a Core Gene SNP phylogenetic tree using maximum likelihood method. Methods A total of 140 STEC strains were isolated from cattle and sheep from 2017 to 2018 in Shandong. These strains were tested for the minimal inhibitory concentrations (MICs) of 27 types of antibiotics in 15 categories using the microbroth dilution method. The detection of extended spectrum beta-lactamases (ESBLs) was conducted by using the double-disk synergy test. Whole genome sequencing was performed, the O:H serotyping, Shiga toxin subtyping and antibiotic resistance gene were analysis. Results The 140 STEC strains constituted 46 O:H serotypes, with O157:H7 accounting for 12.86% (18/140). Two stx1 subtypes and 8 stx2 subtypes were detected, and stx1c+stx2b was the most common subtype, followed by the novel stx2k. Sixteen strains (11.43%) were resistant to at least one antibiotic, and 4 strains (2.86%) were multi-drug resistant. The highest resistance rate to tetracycline was observed in the cattle- and sheep-derived STEC strains (8.57%, 12/140), followed by trimethoprim-sulfamethoxazole (6.43%, 9/140), with 3 strains were ESBLs-producing strains. All strains were sensitive to meropenem and amikacin. A total of 10 categories of 29 antibiotic resistance genes were detected, including the β-lactamase resistance genes blaEC, blaCTX, blaTEM and blaOXA, and fosfomycin resistance gene fosA7 was identified for the first time in STEC. 140 STEC strains formed 38 clusters, each containing the same serotype and ST type, with the O113: H4 ST10 serotype strain being the dominant cluster. Conclusion Cattle and sheep in Shandong Province carry multiple drug-resistant strains with various resistance genes, as well as highly pathogenic O157:H7 strains. It is necessary to strengthen the management of cattle and sheep feces and pathogen monitoring.
