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Isolation, Identification, and Characterization of Enterotoxigenic Escherichia Coli Containing the K88, K99, and 987P Antigens Causing Neonatal Collbacillosis in Piglets in Some Selected Farms in South Vietnam
Thesis Abstract:
Neonatal colibacillosis in pigs is one of the most serious problems in swine production. This study was conducted to determine the occurrence of K88, K99, and 987P Escherichia coli causing neonatal colibacillosis in suckling pigs in some selected pig farms in Cantho and Ho Chi Minh cities in Vietnam.
Rectal swabs were collected from 30 normal and 30 diarrheic piglets. The piglets were divided into two age groups: one-week old and two- to three-weeks old. From each farm, 12 samples were collected, consisting of three samples each from the normal and diarrheic piglet group. E. coli was identified through colonial morphology and biochemical tests. Fimbria! antigens were determined by coagglutination test while the production of heat-labile (LY) and heat-stable (STa) enterotoxins were detected using the rabbit ligated intestinal loop test and suckling mouse assay, respectively.
The K88 antigen was associated with hemolytic E. coli colonies. Organisms which possessed K88 antigen were isolated from 14.3 percent of diarrheic piglets and from 24 percent of normal piglets. Those which possessed the K99 antigens were isolated from 42.9 percent of diarrheic piglets and from 43.2 percent of normal piglets. Those which possessed the 987P antigens were isolated from 2.4 percent of diarrheic piglets. Most cases of diarrhea among the five swine farms studied occurred in three-week-old piglets and were with K88, K99, and 987P E. coli (P<0.01).
Meanwhile, the pattern of occurrence and distribution of E. coli K88, K99, and 987P antigens from piglets, with or without diarrhea, among the five farms were not significantly different. Multiple infections (associated with K88) occurred in 5.9 percent of K99 positive cases. The prevalence of diarrhea associated with E. coli K88 and K99 organisms was highest in two-week-old piglets and lower in older piglets.
Heat labile enterotoxin (LT) was produced by six E. coli K88 isolates obtained from diarrheic piglets but was not produced by nine K88 isolates obtained from normal piglets. Frequencies of produced LT among piglets with and without diarrhea were highly significant (P<0.001).
Heat stable enterotoxin (STa) was strongly produced by 6.7 percent of K88 and 8.9 percent ofK99. It was weakly produced by 26.7 percent of K88, 82.3 percent of K99, and I 00 percent of 987P isolates. However, it was not produced in 8.8 percent of K99 and 2 percent of K88 isolates. The frequency of E. coli producing STa among piglets with and without diarrhea was not significantly different.
Biochemical and coaglutination tests for K88, K99, and 987P, combined with infant mice assay and rabbit ligated intestinal loop test for STa and LT detection, proved useful for the laboratory diagnosis of enterotoxigenic colibaciltosis of pigs.