Antimicrobial resistance in 33 non-O157 Shiga toxin-producing Escherichia coli isolated from human cases from 2011 to 2019

Abstract

Objective: To evaluate the antimicrobial resistance of non-O157 Shiga toxin-producing Escherichia coli (STEC) isolated from human cases. Methods: From 2011 to 2019, 33 non-O157 STEC strains recovered from diarrheal patients from 7 provinces/cities were collected, including Qinghai (1 isolate), Heilongjiang (1 isolate), Guangxi (2 isolates), Shandong (2 isolates), Guangdong (4 isolates), Henan (11 isolates), and Shanghai (12 isolates). Minimum inhibitory concentration (MIC) of 19 antimicrobials were tested by broth microdilution method; O∶H serotypes, Multi-locus sequence typing (MLST) and antimicrobial resistance genes were determined by whole genome sequencing. Results: A total of 33 non-O157 STEC strains were typed into 19 O∶H serotypes and 17 sequence types (STs), respectively. Ten strains were resistant to one or more antibiotics,of which five were multiple drug-resistant (MDR). The resistance rate of tetracycline was 30.3% (10 isolates), and azithromycin resistant strains were detected (12.12%, 4 isolates), but all strains were susceptible to carbapenems. All strains carried the blaEC gene, and the Extended-Spectrum β-Lactamase (ESBL) genotype blaCTX-M-15 were detected (3.0%, 1 isolates). The fosA7 gene was firstly detected in non-O157 STEC strains. Conclusion: MDR, azithromycin resistance, and multiple drug resistance genes were detected in human-derived non-O157 STECs in many regions in China, but they were all susceptible to carbapenems. Our results might guide the clinical treatment of STEC infections.