Prevalence and Molecular Characteristics of Extended-Spectrum β-Lactamase Genes in Escherichia coli Isolated from Diarrheic Patients in China

Li Bai; Lili Wang; Xiaorong Yang; Juan Wang; Xin Gan; Wei Wang; Jin Xu; Qian Chen; Ruiting Lan; Séamus Fanning; Fengqin Li

doi:10.3389/fmicb.2017.00144

Prevalence and Molecular Characteristics of Extended-Spectrum β-Lactamase Genes in Escherichia coli Isolated from Diarrheic Patients in China

Front Microbiol. 2017 Feb 13:8:144. doi: 10.3389/fmicb.2017.00144. eCollection 2017.

Authors

Li Bai¹, Lili Wang², Xiaorong Yang³, Juan Wang⁴, Xin Gan¹, Wei Wang¹, Jin Xu¹, Qian Chen², Ruiting Lan⁵, Séamus Fanning⁶, Fengqin Li¹

Affiliations

¹ Key Laboratory of Food Safety Risk Assessment, Ministry of Health, China National Center for Food Safety Risk Assessment Beijing, China.
² Institute for Nutrition and Food Hygiene, Beijing Key Laboratory of Diagnostic and Traceability Technologies for Food Poisoning, Beijing Center for Disease Prevention and Control Beijing, China.
³ Center for Disease Control and Prevention of Sichuan Province Sichuan, China.
⁴ College of Veterinary Medicine, Northwest A&F University Xianyang, China.
⁵ School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney NSW, Australia.
⁶ Key Laboratory of Food Safety Risk Assessment, Ministry of Health, China National Center for Food Safety Risk AssessmentBeijing, China; UCD-Centre for Food Safety, School of Public Health, Physiotherapy and Sports Science, University College DublinBelfield, Ireland.

Abstract

Background: The emergence and spread of antimicrobial resistance has become a major global public health concern. A component element of this is the spread of the plasmid-encoded extended-spectrum b-lactamase (ESBL) genes, conferring resistance to third-generation cephalosporins. The purpose of this study was to investigate the molecular characteristics of ESBL-encoding genes identified in Escherichia coli cultured from diarrheic patients in China from 2013 to 2014. Materials and Methods: A total of 51 E. coli were confirmed as ESBL producers by double-disk synergy testing of 912 E. coli isolates studied. Polymerase chain reaction (PCR) and DNA sequencing were performed to identify the corresponding ESBL genes. Susceptibility testing was tested by the disk diffusion method. Plasmids were typed by PCR-based replicon typing and their sizes were determined by S1-nuclease pulsed-field gel electrophoresis. Multi-locus sequence typing (MLST) and phylogrouping were also performed. Broth mating assays were carried out for all isolates to determine whether the ESBL marker could be transferred by conjugation. Results: Of the 51 ESBL-positive isolates identified, bla_CTX-M, bla_TEM, bla_OXA, and bla_SHV were detected in 51, 26, 3, 1 of these isolates, respectively. Sequencing revealed that 7 bla_CTX-M subtypes were detected, with bla_CTX-M-14 being the most common, followed by bla_CTX-M-79 and bla_CTX-M-28. Of the 26 TEM-positive isolates identified, all of these were bla_TEM-1 genotypes. All isolates contained one to three large plasmids and 10 replicon types were detected. Of these, IncFrep (n = 50), IncK/B (n = 31), IncFIB (n = 26), IncB/O (n = 14), and IncI1-Ir (n = 8) replicon types were the predominating incompatibility groups. Twenty-six isolates demonstrated the ability to transfer their cefotaxime resistance marker at high transfer rates. MLST typing identified 31 sequence types and phylogenetic grouping showed that 12 of the 51 donor strains belonged to phylogroup B2. Conclusion: This study highlights the diversity of the ESBL producing E. coli and also the diversity of ESBL genes and plasmids carrying these genes in China, which poses a threat to public health.

Keywords: China; Escherichia coli; S1 nuclease digestion; conjugation; extended-spectrum β-lactamase genes; horizontal gene transfer; human.