Phylogenetic group and serotype of E. coli isolates are important risk factors affecting intensity of colibacillosis in broilers

Abstract

The study was conducted on 106 E. coli isolates to determine the phylogenetic group, serotype and carriage of Class 1 integrons in isolates and ascertain their association along with other parameters with vital disease measures in broiler flocks affected with colibacillosis. Out of 32 isolates of which “O” antigen was characterized, serogroup O2 comprising of 12 (37.5%) isolates was most prevalent in the present study. Most of the isolates (85/106; 80.19%) belonged to phylogenetic group B2. Mean apparent morbidity, mortality and case fatality rate (CFR) were 3.77%, 2.32% and 61.49%, respectively. There was significant difference in number of outbreaks reported in different age groups (p less than 0.0001). Also, there was significant association between phylogenetic group and age of outbreak due to E. coli (p=0.024). Comparatively, no significant association was observed between age of outbreaks and serotypes (p=0.980). There was significant association between various disease measures and E. coli isolates affiliated to various phylogenetic groups and serotypes. All the measures (apparent morbidity, mortality and CFR) of disease were highest in outbreaks due to isolates of phylogenetic group B2 and serogroup O20. However, the measures were not significantly affected by the presence of integrons in the E. coli.