Genome Sequences and Phylogenetic Analysis of K88- and F18-Positive Porcine Enterotoxigenic Escherichia coli

Abstract

Porcine enterotoxigenic Escherichia coli (ETEC) continues to result in major morbidity and mortality in the swine industry via postweaning diarrhea. The key virulence factors of ETEC strains, their serotypes, and their fimbrial components have been well studied. However, most studies to date have focused on plasmid-encoded traits related to colonization and toxin production, and the chromosomal backgrounds of these strains have been largely understudied. Here, we generated the genomic sequences of K88-positive and F18-positive porcine ETEC strains and examined the phylogenetic distribution of clinical porcine ETEC strains and their plasmid-associated genetic content. The genomes of porcine ETEC strains UMNK88 and UMNF18 were both found to contain remarkable plasmid complements containing known virulence factors, potential novel virulence factors, and antimicrobial resistance-associated elements. The chromosomes of these strains also possessed several unique genomic islands containing hypothetical genes with similarity to classical virulence factors, although phage-associated genomic islands dominated the accessory genomes of these strains. Phylogenetic analysis of 78 clinical isolates associated with neonatal and porcine diarrhea revealed that a limited subset of porcine ETEC lineages exist that generally contain common toxin and fimbrial profiles, with many of the isolates belonging to the ST10, ST23, and ST169 multilocus sequencing types. These lineages were generally distinct from existing human ETEC database isolates. Overall, most porcine ETEC strains appear to have emerged from a limited subset of E. coli lineages that either have an increased propensity to carry plasmid-encoded virulence factors or have the appropriate ETEC core genome required for virulence. Diarrhea is a major cause of morbidity and mortality to young pigs, resulting in significant production losses for the swine industry (10). Enterotoxigenic Escherichia coli (ETEC) strains are the most common cause of diarrhea in young pigs, resulting in a disease known as enteric colibacillosis (10). Neonatal and postweaning pigs are most susceptible to ETEC. While neonatal ETEC diarrhea is generally well controlled by using fimbria-based vaccines, postweaning enteric colibacillosis has been more difficult to control. Porcine ETEC strains are characterized by the production of specific adhesins and enterotoxins. The adhesins most common in porcine ETEC are fimbrial adhesins K88 (also called F4), K99 (F5), 987P (F6), F41, and F18, as well as afimbrial adhesins such as AIDA-I. Porcine ETEC also produce one or more enterotoxins, including heat-labile enterotoxin (LT), heat-stable enterotoxins a and b (STa and STb), and EAST1 toxin (33). These and other described porcine ETEC virulence factors have mostly been localized to plasmids. Additionally, F18-positive porcine E. coli strains implicated in edema disease and diarrhea sometimes possess the Shiga toxin-encoding gene (stx 2e ) within their chromosomes (16).Analyses of human ETEC strains have revealed ...

Plasmid-Mediated Resistance to Cephalosporins and Fluoroquinolones in Various Escherichia coli Sequence Types Isolated from Rooks Wintering in Europe

“…STC10 includes pathogenic heterogeneous enteroaggregative E. coli (EAEC), enterotoxigenic E. coli (ETEC), ExPEC, as well as commensal E. coli strains found in humans and food-producing animals (14,37,38). STC10 members contributing to the spread of various ESBL and AmpC genes are widely described in relation to hospital-onset infections (39,40), but they have also been reported in food animals in the Netherlands, the United Kingdom, and France (41)(42)(43).…”

“…Moreover, the STC155 members were associated with various infections in livestock in Europe (42,43). ESBL-producing STC23 is commonly isolated in hospitals in Spain and France (45,46), but this clonal complex has also been detected in samples obtained from foodproducing animals and chicken meat (38,41,42).…”

Allele Variants of Enterotoxigenic Escherichia coli Heat-Labile Toxin Are Globally Transmitted and Associated with Colonization Factors

“…This suggests that since the majority of the colonization factors and toxin are normally encoded on plasmids, the different LT variants have been acquired together with certain colonization factors on the same plasmid or a compatible coplasmid(s) (31,38,39). Although further analyses are required to demonstrate whether LT and colonization factors are physically located on the same plasmid, our data suggest that the alleles of both toxins and CFs are conserved within lineages and hence might have been acquired simultaneously by one ancestor strain at one point and then spread clonally.…”

Hybrid Shiga Toxin-Producing and Enterotoxigenic Escherichia sp. Cryptic Lineage 1 Strain 7v Harbors a Hybrid Plasmid

“…ETEC strains frequently contain more than one plasmid, one of which, not necessarily encoding ST, often encodes a fimbrial adhesin referred to as a colonization factor (CF) (2,28). ETEC strains isolated from humans elaborate human-specific CFs, while porcine ETEC isolates primarily harbor plasmids encoding the CF K88 or F18 (1,2,7). Not all ETEC strains carry known CFs, and these strains may represent CF-negative strains or possess CFs that are not yet identified (22).…”