ABSTRACT
Escherichia coli isolates from avian colibacillosis were examined for adherence-associated characteristics and post-colonisation pathogenicity. The adherence-associated characteristics studied included expression of pili, ability to partition with a hydrophobic phase, and ability to bind to Biosilon plastic polar-surfaced microcarriers. None of the adherence-associated characteristics correlated absolutely with post-colonisation pathogenicity, and thus in vitro tests for these adherence-associated characteristics cannot be used to predict whether any given E. coli avian colibacillosis isolate will exhibit post-colonisation pathogenicity. The isolation of strain BT7 from avian colibacillosis, a piliated E. coli strain which binds to Biosilon polar-surfaced plastic microcarriers, but is not pathogenic, is reported.
ABSTRACT
At hatching, the level of maternal antibody to E. coli in chicks, measured by ELISA was found to be 55 to 62% of that of the hen. It declined to an undetected level at 21 days of age. A sonicated experimental vaccine when given with a Freund's complete adjuvant to breeder hens produced the highest antibody titres and which were maintained for at least 160 days (end of the experiment) as well as providing the progeny protection. Progeny of hens with high antibody titre challenged with the homologous bacteria at 7 and 14 days of age exhibited total resistance, while those challenged at 21, 34 and 45 days of age, when antibody titres were undetectable, still showed 30 to 40% higher resistance than the control group. The results indicated a correlation between the hen's antibody titre and percentage of survival of her progeny. Challenged progeny with a heterologous strain exhibited no protection. Hens which were vaccinated with a bivalent vaccine gave rise to chicks which were protected against both serotypes.
ABSTRACT
An enzyme-linked immunosorbent assay (ELISA) was modified for detection of antibodies against the two main pathogenic serotypes of Escherichia coli: serotypes O78:K80 and O2:K1. The ELISA was a more sensitive and repeatable test than the indirect hemagglutination test (IHT), which is a common method for detecting antibodies against E. coli. Cross-reactivity between the two strains was measured by reacting antisera of each serotype against homologous and heterologous antigens. The results suggest that aside from similar determinants expressed by the two serotypes, serotype O2:K1 expresses more strain-specific determinants than does O78:K80. Comparison of mean antibody titers of immunized chicks by IHT and ELISA along the primary response revealed that during the first 15 days after immunization with inactivated E. coli, the titers in both tests were parallel. After 15 days post-immunization, antibody titers measured by IHT decreased rapidly, whereas titers measured by ELISA decreased only slightly. In addition, a higher correlation was found between titers detected by ELISA and survival through challenge with E. coli than between titers detected with IHT and survival through challenge. The results suggest that the ELISA is a better test for detection of antibody in flocks suspected of being infected with E. coli.
