Characterization and virulence clustering analysis of extraintestinal pathogenic Escherichia coli isolated from swine in China

Abstract

BackgroundSwine extraintestinal pathogenic Escherichia coli (ExPEC) is an important pathogen that leads to economic and welfare costs in the swine industry worldwide, and is occurring with increasing frequency in China. By far, various virulence factors have been recognized in ExPEC. Here, we investigated the virulence genotypes and clonal structure of collected strains to improve the knowledge of phylogenetic traits of porcine ExPECs in China.ResultsWe isolated 64 Chinese porcine ExPEC strains from 2013 to 14 in China. By multiplex PCR, the distribution of isolates belonging to phylogenetic groups B1, B2, A and D was 9.4%, 10.9%, 57.8% and 21.9%, respectively. Nineteen virulence-related genes were detected by PCR assay; ompA, fimH, vat, traT and iutA were highly prevalent. Virulence-related genes were remarkably more prevalent in group B2 than in groups A, B1 and D; notably, usp, cnf1, hlyD, papA and ibeA were only found in group B2 strains. Genotyping analysis was performed and four clusters of strains (named I to IV) were identified. Cluster IV contained all isolates from group B2 and Cluster IV isolates had the strongest pathogenicity in a mouse infection model. As phylogenetic group B2 and D ExPEC isolates are generally considered virulent, multilocus sequence typing (MLST) analysis was performed for these isolates to further investigate genetic relationships. Two novel sequence types, ST5170 and ST5171, were discovered. Among the nine clonal complexes identified among our group B2 and D isolates, CC12 and CC95 have been indicated to have high zoonotic pathogenicity. The distinction between group B2 and non-B2 isolates in virulence and genotype accorded with MLST analysis.ConclusionThis study reveals significant genetic diversity among ExPEC isolates and helps us to better understand their pathogenesis. Importantly, our data suggest group B2 (Cluster IV) strains have the highest risk of causing animal disease and illustrate the correlation between genotype and virulence.Electronic supplementary materialThe online version of this article (doi:10.1186/s12917-017-0975-x) contains supplementary material, which is available to authorized users.

Extended Phylogeny and Extraintestinal Virulence Potential of Commensal Escherichia coli from Piglets and Sows

“…The analysis of the distribution of VGs within phylogenetic groups among E. coli from sows revealed no significant differences, the one exception being isolates of phylogroup A, which carried VGs significantly less frequently. Our results demonstrating the virulence potential of group B2 in isolates from piglets are consistent with those presented in the first, above-mentioned report concerning ExPEC [26]. On the other hand, it was also reported that VGs were distributed among four main phylogroups without significant differences in commensal porcine isolates [12], which is consistent with our analysis concerning E. coli from sows.…”

“…According to the definition (Johnson et al [10]) 17.3% of E. coli isolates from piglets and 7.9% from sows were classified as ExPEC, despite the fact that they were derived from healthy animals. The other isolates in our collection also harbored VGs associated with the ability to cause extraintestinal disease, not only in swine but also in humans [4,26]. The results showed significant differences between isolates from piglets and sows.…”

“…Interestingly, the phylogenetic structure of porcine ExPEC is similar to the phylogeny of the commensal isolates. ExPEC from diseased pigs mostly belonged to phylogroups A and B1, while phylogroup B2 is usually the least numerous [6,26,52,53]. It has been reported that ExPEC isolated from piglets with septicemia, often pathogenic in experimental infections, fall into groups A and B1 [54].…”

“…Many studies have indicated that the most highly virulent human ExPEC strains, which cause urinary tract infection, neonatal septicemia, or meningitis, belong to group B2 or D and that the strains of these phylogroups harbor more virulence factors than the strains of the A and B1 groups [7,13]. Moreover, it has been reported that porcine ExPEC B2 isolates contained more virulence-associated genes than non-B2 isolates and these isolates had the strongest pathogenicity in a mouse infection model [26]. Another study found no significant differences in means (ranges) of VGs across different phylogenetic groups among ExPEC from pigs [6].…”

“…Infections caused by ExPEC strains occur worldwide and are associated with great economic cost [24]. ExPEC is an important pathogen in the swine industry, in several countries, responsible for substantial economic losses [25][26][27]. Porcine ExPEC is an important pathogen causing UTI-a significant cause of death in adult animals [6].…”