Frequency of Diarrheagenic Virulence Genes and Characteristics in Escherichia coli Isolates from Pigs with Diarrhea in China

Abstract

Intestinal pathogenic Escherichia coli (InPEC) is a leading cause of postweaning diarrhea (PWD) in pigs. Here, a total of 455 E. coli strains were isolated from small intestinal content or feces from pigs with PWD in 56 large-scale (>500 sows; 10,000 animals per year) swine farms between 2014 and 2016. The frequency of occurrence of selected virulence factors for InPEC pathotypes was detected in 455 isolates by real-time PCR. Sequence types (STs), pulsed-field gel electrophoresis (PFGE), and antimicrobial susceptibility profiles of 171 E. coli isolates from 56 swine farms were further determined. The heat-labile enterotoxin (LT) was the most common (61.76%), followed by heat-stable enterotoxin (STb) (33.19%), stx2e (21.54%), STa (15.00%), eae (8.98%), cnf2 (5.71%), stx2 (5.71%), F18 (3.25%), and F4 (2.25%) with rates varying by geographic area and year of isolation. Notably, hybrids of E. coli isolates were potentially more virulent, as some InPEC hybrids (virotype F18:LT:eae:stx2e) can rapidly cause cell death in vitro. Genotypic analysis revealed that the most prominent genotype was ST10 (12.87%). The PFGE patterns were heterogeneous but were not ST or virotype related. A total of 94.15% of isolates were multidrug-resistant, with average resistance rates ranging from 90.05% for nalidixic acid to 2.34% for meropenem. Our investigation contributes to establishing the etiology of diarrhea and developing intervention strategies against E. coli-associated diarrheal disease in the future.

Genome Characterization of mcr-1–Positive Escherichia coli Isolated From Pigs With Postweaning Diarrhea in China

“…Of these, 171 E. coli isolates were further screened by antimicrobial susceptibility testing, and the resistance rate of colistin was 20.47% (6). From these 35 colistin-resistant E. coli, we observed ST4214 was a major clone (6/35, 17.14%) based on the multilocus sequence typing and caused severe damage to IPEC-J2 cells (6). Then, ST4214 E. coli CAU15014, CAU15134, and CAU16060 were selected from different swine farms (one isolate per farm), and two MDR aEPEC isolates (E. coli CAU16175 and CAU16177) were randomly chosen for WGS.…”

“…The occurrence of antimicrobial resistance and prevalence of multidrug resistance (MDR) Gram-negative Enterobacteriaceae has been increasing worldwide between humans and animals (13). In the cases of PWD, antimicrobial treatment has been widely used and caused severe drug resistance in DEC (1,6,14). In our previous study, among the 171 E. coli isolates, 94.15% of the strains were MDR, with antimicrobial resistance rates ranging from 2.34% for meropenem to 90.05% for nalidixic acid (6).…”

“…In the cases of PWD, antimicrobial treatment has been widely used and caused severe drug resistance in DEC (1,6,14). In our previous study, among the 171 E. coli isolates, 94.15% of the strains were MDR, with antimicrobial resistance rates ranging from 2.34% for meropenem to 90.05% for nalidixic acid (6). Among the ETEC strains that cause PWD, resistance to apramycin, neomycin, trimethoprim sulfonamide, and colistin has been increasingly observed (1).…”

“…All of these DECs possess diverse virulence factors, which are encoded by virulence genes and are responsible for their pathogenicity (5). Enterotoxigenic E. coli strains typically produce one or two toxins, heat-labile enterotoxin (LT) encoded by ltc, and heat-stable enterotoxin (ST) encoded by st (6). In pigs, STEC strains are characterized by producing the Shiga-like toxin variant Stx2e encoded by stx2e (7).…”

“…Hence, aEPEC strains are defined by eae + , bfpA − , and stx − (9). Three pathotypes (ETEC, STEC, EPEC) are major DEC causing postweaning diarrhea (PWD) in pigs, and many hybrids of E. coli (ETEC/STEC, ETEC/STEC/EPEC) are present during PWD (6,10). The recent data from The Global Enteric Multicenter Study showed that tEPEC and ETEC associated with a higher risk of fatal outcomes in children younger than 24 months with moderate to severe diarrhea (11).…”