In Vivo and in Vitro Colonization Patterns of AIDA-I–Positive Escherichia Coli Isolates from Piglets with Diarrhea

Abstract

Abstract. Transmission electron microscopy (TEM) was used to characterize the colonization patterns of 3 pathogenic Escherichia coli strains: PD58 and PD149 of the AIDA-I/STb/EAST1 pathotype, serogroup O: ND (not determined), and PD31 of the LT/STb/EAST1 pathotype, serogroup O149. These strains were isolated from diseased piglets and caused diarrhea in experimentally inoculated, newborn, colostrum-deprived pigs. In this study, intestinal tissues from newborn pigs experimentally infected with a high inoculum (20 ml containing 10 10 cfu) were harvested and examined for bacterial colonization using light microscopy. A nonaqueous perfluorocarbon fixation method was used to preserve the glycocalyx of the microvillus border in tissues collected for TEM. Transmission electron micrographs revealed that E. coli strain PD149 displayed long flexible fimbrialike structures that intimately attached the bacteria both to the microvillus border of the upper colon and to adjacent bacteria. In vitro, this strain demonstrated the localized adherence pattern to HEp-2 cells characteristic of enteroaggregative E. coli (EAggEC). Both PD58 and PD31 strains colonized the upper colon through the formation of a biofilm, also characteristic of EAggEC. Strains PD58 and PD31 adhered poorly to HEp-2 cells in vitro, although these demonstrated a colonization pattern suggestive of diffuse and aggregative adherence, respectively. These findings suggest that strains PD58 and PD149, expressing the AIDA-I, factor and strain PD31 represents hybrid pathotypes of diarrheagenic E. coli and that they probably cause diarrhea in piglets through differing mechanisms.Diarrhea is one of the most common problems affecting neonatal pig survival worldwide. The highest incidence of clinically relevant diarrhea occurs in the first 3 to 5 days of life, and enterotoxigenic Escherichia coli (ETEC) is the most common agent identified. 1,10,20 Piglets are exposed to massive numbers of bacteria at the time of birth. The majority of these are nonpathogenic anaerobes, but potentially pathogenic E. coli are also present. The pH of the stomach and the duodenum at birth is relatively alkaline and few digestive enzymes are produced, allowing a favorable environment for bacterial growth. 8 Enterotoxigenic E. coli colonize the small intestine of the piglet in the first few hours of life by attaching or tethering to the microvillus border of the enterocytes with one of the ETEC fimbrial factors F4 (K88), F5 (K99), F6 (987P), F18, or F41. 5 The bacteria then produce 1 or more of 3 enterotoxins, heat-labile toxin (LT), heat-stable toxin 'a' (STa), or heat-stable toxin 'b' (STb), which act directly on enterocytes through different pathways to stimulate a net secretory watery diarrhea 8 with accompanying dehydration, electrolyte imbalances, including hyperkalemia, and acidosis. It is the combination of these pathophysiological changes that often results in the death of a piglet.In an increasing number of cases of enteric colibacillosis in piglets, ETEC strains isolated in the bacte...

Prevalence and characterization of virulence genes in Escherichia coli isolated from piglets suffering post‐weaning diarrhoea in Shandong Province, China

“…In the present study, for the most common colonization factors AIDA‐I and paa , the AIDA‐I‐positive strains also carried EAST1 (21/33) and irp2 (12/33); the paa‐ positive strains also contained EAST1 (12/27) and irp2 (11/27). Similar findings have been reported in numerous studies (Ngeleka et al, ; Pritchard, Ngeleka, & Middleton, ; Ravi et al, ).…”

A homolog of the O157 urease-encoding O island 48 is present in porcine O149:H10 enterotoxigenicEscherichia coli

“…This GI includes potential virulence genes such as the urease genes that may be involved in acid resistance [17] and the genes for Iha and AIDA-I that may play a role in adherence [29,40]. The AIDA-I adhesin has been associated primarily with porcine ETEC and Stx2e strains that carry the F18 fimbriae [16,29], but has also been reported in F4-positive O149 ETEC [37]. Disease due to ETEC in pigs is quite different from that due to O157 EHEC in humans and involves different areas of the intestine.…”

Modulation of transcription and characterization of the promoter organization of the autotransporter adhesin heptosyltransferase and the autotransporter adhesin AIDA-I

“…In these animals, the presence of AIDA-Ipositive strains appears to be associated with F18 fimbriae and oedema disease (Niewerth et al, 2001;Mainil et al, 2002). That AIDA-I augments virulence in intestinal disorders is supported by findings in vivo that show that expression of AIDA-I in porcine strains increases the onset of diarrhoea in weaned piglets (Pritchard et al, 2004).…”