Determination of Lethal Effects of Escherichia coli and it’s Toxin Isolated from Chicken

Abstract

The study was conducted to isolate and identify E. coli from apparently healthy broilers and layers from Rana Poultry Farm (Uttar Gobindapur, Dinajpur), Panch Mile Poultry Farm (Mohabolipur, Dinajpur), Somai Poultry Farm (Uttar Sadipur, Dinajpur), Achia Poultry Farm (Barail, Dinajpur) and M. R. Poultry Farm (Uttar Sadipur, Dinajpur), during the period of January to May 2010 and characterize their ability to produce enterotoxin and to determine the pathogenicity of the isolates. A total of 50 fecal samples were collected from broiler (n=25) and layer (n=25) chickens and subjected to primary isolation by propagating in nutrient broth followed by culture on different agar media. Gram’s staining and hanging drop techniques were also performed. Biochemical properties of the isolates were studied and reaction in TSI agar slant was also observed. Pathogenicity of 12 representatives E. coli isolates, six from each source were determined by lethality assay in 12 day-old embryonated eggs and in day-old chick’s models. £. coli was isolated successfully from all the samples. All the E. coli isolates were found to produce bright pink colonies on MacConkey agar and characteristic metallic sheen colonies on the EMB agar. In Gram’s staining technique, all the isolates were pink coloured, small rod shaped Gram negative bacilli and in the hanging drop technique they were motile. Reactions in TSI agar slant revealed yellow slant and butt with gas but no hydrogen sulphide production. Almost all the E. coli isolates fermented dextrose, maltose, lactose, sucrose and mannitol with the production of both acid and gas. The results of MR and indole test of the E. coli isolates were positive but V-P test was negative. In the embryo lethality assay, E. coli isolates from broiler and layer were found to be more virulent which caused 100% death of the embryos. Most of the embryos died between day-1 and day-2 PI. Chick lethality assay indicated that all the EF. coli isolates were virulent as the mortality rate was 100%. The death of chicken occurred within 40 to 140 h following inoculation. Between these two lethality assay models, avian embryo lethality assay was found to be most suitable to discriminate between virulent and avirulent isolates compared to day-old chick lethality assay. In conclusion, these results showed that E. coli isolated from broiler and layer sources virulence and avian embryo lethality assay was assumed to be the best model! for discriminating virulent and avirulent E. coli.