Escherichia coli O157:H7-secreted cytotoxins are toxic to enterocytes and increase Escherichia coli O157:H7 colonization of jejunum and descending colon in cattle

Abstract

, T. 2008. Escherichia coli O157:H7-secreted cytotoxins are toxic to enterocytes and increase Escherichia coli O157:H7 colonization of jejunum and descending colon in cattle. Can. J. Anim. Sci. 88: 41Á50. Enterohemorrhagic Escherichia coli (EHEC) O157:H7-secreted cytotoxins are toxic to target cells and enhance colonization of intestinal tissues in disease-susceptible animals. It is unclear what role, if any, EHEC O157:H7-secreted cytotoxins play in the colonization of intestinal tissues of healthy reservoir animals. We previously reported that EHEC O157:H7 colonization sites were associated with focal hemorrhages in the jejunum and descending colon of persistent shedding cattle, suggesting a potential role for cytotoxins in EHEC O157:H7 colonization. We have used a traditional EHEC O157:H7 IVOC adherence assay and a novel lawn assay to examine the role of EHEC O157:H7-secreted cytotoxins in EHEC O157:H7 strain colonization of the jejunum and descending colon of non-persistent and persistent shedding cattle. Four EHEC O157:H7 strains that were previously reported to differentially colonize cattle produced cytotoxins that were differentially active against epithelial cells from the jejunum and descending colon. There was a relationship between EHEC O157:H7-secreted cytotoxin activity and strain adherence for epithelial cells from the jejunum and descending colon of cattle. There was also a greater susceptibility of epithelial cells from the jejunum and descending colon to EHEC O157:H7-secreted cytotoxins of persistent shedding cattle compared with non-persistent shedding cattle. Addition of the most active secreted cytotoxins from EHEC O157:H7 R318N to the IVOC adherence assays significantly increased the adherence of the most (R318N) and least (H4420N) virulent EHEC O157:H7 strain to intestinal tissues. The current study supports a role for EHEC O157:H7-secreted cytotoxins in enhancing EHEC O157:H7 colonization of intestinal tissues of cattle.Key words: Escherichia coli O157:H7, cattle, intestine, cytotoxins, colonization Baines, D., Masson, L. et McAllister, T. 2008. Les cytotoxines se´cre´te´es par Escherichia coli O157:H7 sont toxiques pour les ente´rocytes et favorisent la colonisation du je´junum et du coˆlon descendant des bovins par le microorganisme. Can. J. Anim. Sci. 88: 41Á50. Les cytotoxynes se´cre´te´es par la souche O157:H7 d'Escherichia coli ente´ro-he´morragique (EHEC) sont toxiques pour les cellules cibles et favorisent la colonisation des tissus intestinaux chez les animaux sensibles a`la maladie. Le roˆle e´ventuel des cytotoxynes de EHEC O157:H7 dans la colonisation des tissus intestinaux des porteurs sains n'est toutefois pas claire. Ante´rieurement, les auteurs avaient signale´que les sites colonise´s par EHEC O157:H7 e´taient associe´s a`des foyers d'he´morragie dans le je´junum et le coˆlon descendant des animaux excre´teurs, signe que les cytotoxynes libe´re´es par le microorganisme pourraient intervenir. Ils ont recouru a`une e´preuve classique d'adhe´rence IVOC pour EHEC O157:H7 ainsi ...

Escherichia coli O157:H7 Strain Origin, Lineage, and Shiga Toxin 2 Expression Affect Colonization of Cattle

“…Only a few studies are available that have examined the role of lineage or origin on Shiga toxin activities or the promotion of E. coli O157:H7 colonization of cattle. Inclusion of Stx2 enhances the colonization of a human-origin lineage I strain by a factor of 100 (4) and, in another study (6), inclusion of the cytotoxin mixture from a human-origin lineage I strain increased colonization of a bovine-origin strain 10-fold compared to a 4-fold change for a human-origin lineage I strain. This suggested that the bovine-origin strains could utilize the cytotoxins to enhance their own colonization.…”

“…Mature cattle are considered the primary reservoir for E. coli O157:H7 and historically were reported to have no symptoms or pathologies (17,23,38); this was attributed both to a lack of receptors for a critical E. coli O157:H7 virulence factor, Shiga toxin 1 (Stx1 [29]), and to a differential expression of type III protein secretion system effector molecules such as EspA, EspD, and Iha (25,30) in cattle compared to humans. In 2008, it was established for the first time that E. coli O157:H7 causes mild to severe intestinal pathology in persistent shedding cattle (5,26) and that the secreted cytotoxins enhanced E. coli O157:H7 colonization of intestinal tissues of cattle (6). This suggested that cattle were susceptible to E. coli O157:H7 infection and that previously discounted virulence factors could influence the amount of colonization in cattle.…”

“…The secreted cytotoxins from a human-origin E. coli lineage I strain have been shown to enhance the colonization of a bovine-origin E. coli lineage I strain that had significantly lower colonization on its own (6). To establish the role, if any, of the secreted cytotoxins produced by E. coli lineages in tissue colonization, the colonic cell line was exposed to about 80 ng of secreted cytotoxins from each of the E. coli O157:H7 strains in conjunction with 10 6 CFU/ml of the least adherent E. coli O157:H7 strain, ECI 1717.…”

“…Necropsy samples were obtained from eight Hereford ϫ Angus steers using standard methods (5,6,38). Jejunum tissues (30 cm) were removed within 2 min of release of the intestinal tract from the carcass and each piece was placed in 200 ml of oxygenated Dulbecco modified Eagle medium (DMEM; high glucose; HyClone, Logan, UT) supplemented with bovine albumin.…”

“…E. coli O157:H7 secreted cytotoxins were isolated and concentrated by using a combination of centrifugation and ultrafiltration as described previously (6). Briefly, the strains were grown in 15 ml of M9 media for 5 days.…”