Naslov
Differentiated attaching and effacing activities of porcine F4^+ enterotoxigenic and nonenterotoxigenic Escherichia coli strains

Autori
Vijtiuk, Nada ; Bilić, Vitomir ; Harapin, Ivica ; Vrbanac, Ivan ; Valpotić, Ivica

Izvornik
Periodicum biologorum (0031-5362) 103 (2001), 1; 21-27

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Intestinal adherence; E. coli; pig

Sažetak
Background and purpose: In contrast to the development of vaccines against neonatal colibacillosis, comparatively little progress has been made in the development of vaccines against postweaning enterotoxigenic Escherichia coli (ETEC) infections in swine. The vaccine candidate attenuated E. coli strains lacking plasmid encoding the heat-labile (LT) and heat-stable(STa and STb) enterotoxins were used as a live whole cell bacterins. Differentiation between colonization patterns and histopathological appearance of the small intestine of pigs that have been immunized with F4ac^+ either ETEC strain M1823 or recombinant/authentic non-ETEC strains 2407/1466, respectively, was studied in order to determine whether (or not) the fimbrial/toxin antigens produce morphologic changes in the intestinal mucosa. We also monitored the adverse effect of the oral immunization with these strains on the pigs health in a model of postweaning colibacillosis. Materials and methods: Twenty-five 4-week-old pigs (from a herd that was previously found to be highly susceptible to the adhesion by F4^+ E. coli) were intragastrically inoculated (via orogastric tube) with either F4ac^+ (1466 or 2407) or F4^- (1467) nonenterotoxigenic E. coli (ETEC) strains, respectively. The pigs from fourth group were inoculated with F4ac^+ ETEC strain M1823 and the remaining 5 pigs that received broth containing 1.2% sodium bicarbonate were kept as noninoculated controls. The pigs were examined daily during the period of 12 days. In this model, three conditions were observed in F4-susceptible pigs: (1) acute fatal diarrheal disease ; (2) moderate diarrhea and weight loss, and (3) no diarrhea and weight loss. The incidence of diarrhea, weight gain/loss rates, fecal shedding of the inoculum strain, and ultrastructural alterations in the villous epithelium of the small intestine were recorded. Results and conclusions: Pigs inoculated with strain 2407 had much lower incidence of diarrhea and the highest weight gain rate. Only pigs inoculated with 2407 had > 10^5 viable E.coli/10-cm segment of small intestine. The highest numbers of bacteria (9.6 x 10^7 CFU/ml and 4.3 x 10^6 CFU/ml) for each segment were recorded on days 6 and 12 after inoculation, respectively, in pigs inoculated with strain M1823. Control and 2407-inoculated pigs (25% and 30%, respectively) gained weight substantially faster than did 1466- (7%) or M1823-inoculated pigs (10%). Ultrastructural examination of ileum from 1466- and M1823-inoculated pigs revealed moderate to severe lesions of microvilli of epithelial cells, respectively. There were no substantial differences in the brush border surface of ileal enterocytes between control pigs (with intact microvilli) and 1467- or 2407-inoculated pigs. However, the microvilli from 2407-inoculated pigs exhibited a minor structure irregularity caused by adhering E. coli cells. Conversely, the brush border membranes of M1823-inoculated pigs were heavily damaged and the epthelium layer of villi was extensively disrupted. The results of this study indicate that different protective antigens delivered orally to pigs through vaccine candidate non-ETEC strains 1466 and 2407 can induce distinct colonization and attaching-effacing patterns in the small intestine, and hence, may produce various grades of lesions on the microvillus membranes of epithelial cells. Non-ETEC strain 2407 expressing F4ac^+ antigen induced only a mild microvillous damage, compared to the findings in pigs that were infected with a virulent F4ac^+ ETEC strain M1823.

Izvorni jezik
Engleski

Znanstvena područja
Veterinarska medicina

POVEZANOST RADA