The aim of this research is to establish in vivo and in vitro pathogenicity of 25 E.coli samples obtained from poultry bearing the Swollen Head Syndrome (SHS). In vivo pathogenicity was determined by inoculation in one-day old pathogens free, chicks using inoculation in 4 different ways: intracardiac, aerial sac, oral and tracheal. In vitro pathogenicity was determined by E.coli-sterile supernatant inoculation in a Vero cells culture and observed whether cellular death occurred or not in a period of 24, 48 and 72 hours. Regarding the influence of the cytotoxic effect in general death rate of one-day old chicks, it was concluded that due to the non-existence of statistical significance among the average values obtained with samples of E. coli, producers and non- producers of verotoxins, the cytotoxic effect did not affect the overall death rate, i.e. the cytotoxic in samples of E. coli cannot be related as pathogenic. On the basis of results obtained due to different inoculation way death rate was higher when used through intracardiac (73.6%) and aerial sac (68%) ways. The results of the pathogenicity test in vivo showed 64% of samples of E. coli isolated from birds with SHS. In this study, these were considered of high pathogenicity.
Escherichia coli; colibacillosis; chickens; SHS; verotoxins