title: Relationship between heat-labile enterotoxin secretion capacity and virulence in wild type porcine-origin enterotoxigenic Escherichia coli strains.
abstract: Heat-labile enterotoxin (LT) is an important virulence factor secreted by some strains of enterotoxigenic Escherichia coli (ETEC). The prototypic human-origin strain H10407 secretes LT via a type II secretion system (T2SS). We sought to determine the relationship between the capacity to secrete LT and virulence in porcine-origin wild type (WT) ETEC strains. Sixteen WT ETEC strains isolated from cases of severe diarrheal disease were analyzed by GM1ganglioside enzyme-linked immunosorbent assay to measure LT concentrations in culture supernatants. All strains had detectable LT in supernatants by 2 h of culture and 1 strain, which was particularly virulent in gnotobiotic piglets (3030-2), had the highest LT secretion level all porcine-origin WT strains tested (P<0.05). The level of LT secretion (concentration in supernatants at 6-h culture) explained 92% of the variation in time-to-a-moribund-condition (R2 = 0.92, P<0.0001) in gnotobiotic piglets inoculated with either strain 3030-2, or an ETEC strain of lesser virulence (2534-86), or a non-enterotoxigenic WT strain (G58-1). All 16 porcine ETEC strains were positive by PCR analysis for the T2SS genes, gspD and gspK, and bioinformatic analysis of 4 porcine-origin strains for which complete genomic sequences were available revealed a T2SS with a high degree of homology to that of H10407. Maximum Likelihood phylogenetic trees constructed using T2SS genes gspC, gspD, gspE and homologs showed that strains 2534-86 and 3030-2 clustered together in the same clade with other porcine-origin ETEC strains in the database, UMNK88 and UMN18. Protein modeling of the ATPase gene (gspE) further revealed a direct relationship between the predicted ATP-binding capacities and LT secretion levels as follows: H10407, -8.8 kcal/mol and 199 ng/ml; 3030-2, -8.6 kcal/mol and 133 ng/ml; and 2534-86, -8.5 kcal/mol and 80 ng/ml. This study demonstrated a direct relationship between predicted ATP-binding capacity of GspE and LT secretion, and between the latter and virulence.
authors.affiliation: School of Veterinary Medicine and Biomedical Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska, United States of America.
authors.forename: Prageeth
authors.initials: P
authors.lastname: Wijemanne
authors.affiliation: School of Veterinary Medicine and Biomedical Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska, United States of America; Canada Immunoassay Development, Windsor, Ontario, Canada.
authors.forename: Jun
authors.initials: J
authors.lastname: Xing
authors.affiliation: School of Veterinary Medicine and Biomedical Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska, United States of America; Vaccine and Infectious Disease Organization-International Vaccine Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
authors.forename: Emil M
authors.initials: EM
authors.lastname: Berberov
authors.affiliation: Department of Statistics, University of Nebraska-Lincoln, Lincoln, Nebraska, United States of America.
authors.forename: David B
authors.initials: DB
authors.lastname: Marx
authors.affiliation: Department of Veterinary Science, South Dakota State University, Brookings, South Dakota, United States of America.
authors.forename: David H
authors.initials: DH
authors.lastname: Francis
authors.affiliation: School of Veterinary Medicine and Biomedical Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska, United States of America.
authors.forename: Rodney A
authors.initials: RA
authors.lastname: Moxley
mesh_terms: D000818:Animals; D058947:Bacterial Secretion Systems / Q000235:genetics / Q000378:metabolism*; D001427:Bacterial Toxins / Q000235:genetics; D003967:Diarrhea / Q000382:microbiology / Q000662:veterinary; D054307:Enterotoxigenic Escherichia coli / Q000235:genetics / Q000472:pathogenicity* / Q000502:physiology*; D004768:Enterotoxins / Q000235:genetics / Q000378:metabolism*; D004927:Escherichia coli Infections / Q000382:microbiology / Q000662:veterinary; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D013552:Swine; D013553:Swine Diseases / Q000382:microbiology; D014774:Virulence
chemical_list: D058947:Bacterial Secretion Systems; D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; C027538:heat-labile enterotoxin, E coli