The present study was undertaken to establish the incidence of E. coli infection in broiler chickens reared in Gonda district of North Eastern Plain Zone of Uttar Pradesh. Two broiler farms from each Tehsil of the district were selected on the basis of stratified random sampling. A total number of 483 naturally dead broiler chickens from 8 private farms from Gonda district of North Eastern Plain Zone of Uttar Pradesh were collected within 6 hours of death throughout the year (June 2018 - May 2019). The birds were of different age group and of both sexes. After post mortem examination, all the gross lesions were recorded. For bacteriological study, materials from grossly suspected birds with E. coli infection were collected. The pieces of liver, lungs, heart, intestine, and spleen were aseptically collected from the dead birds showing gross pathological lesions of suspected E. coli infection i.e. yellow/white sero-fibrinous covering over liver, heart, and peritoneum, congestion of lung and heart, intestinal haemorrhages and necrotic foci on liver. They were kept in sterile vials separately and brought to the Veterinary Microbiology Laboratory under ice coverage for further study. The method described by Cruickshank et al. (1975) was used for the isolation of E. coli and the isolates were identified on the basis of morphology, motility, and colony characteristics and bio-chemicals properties as per the method of Edwards and Ewing (1972).

The samples (483 dead birds) were collected from Gonda district of North Eastern Plain Zone of Uttar Pradesh, suspected to be suffering from colibacillosis. The diagnosis was confirmed on the basis of pathognomic lesions, and isolation and identification of the causative organism. The overall incidence of colibacillosis was 38.09% (184 samples were positive out of 483 samples) which was similar to the reports of Phukan (1988) who reported 50.84% overall incidence of E. coli infection and Singh et al. (2018) who observed 53.37% positive cases of colibacillosis. The incidence in the present study was also similar with the findings of Chandra et al. (2008) and Ashraf et al. (2015) in the broiler chicken. The detail incidence of farms is shown in table 1.

The gross changes of liver were found as enlarged, congested and covered with thick yellow/white serofibrinous covering. The serofibrinous membrane covered the liver either partially or completely that differs with degree and severity of infection (Fig. 1 and 2).

In intestine hemorrhages, congestion and edematous swelling were noted. Heart was also covered with thick yellow/white serofibrinous covering (Fig. 1 and 2). In severe E. coli infection, the serofibrinous membrane covered all the visceral organs continuously (Fig. 1 and 2). The gross lesions observed in the present study corroborated with the findings of Tonu et al. (2011), Daud et al. (2014), Parwez et al. (2015) and Singh et al. (2018).

Among tested 483 samples from 8 private farms from Gonda district, 184 (38.09%) were found to be suggestive of E. coli giving typical large (2-3 mm) lactose fermenting pink coloured colonies on Mac Conkey’s agar plate (Fig. 3). They again produced characteristic ‘metallic sheen’ on EMB agar (Fig. 4). On Gram staining during morphological study, they produced pink coloured, rod shaped ones (that is gram negative) with characteristic arrangement (Fig. 5). These finding were in accordance with Edward and Ewing (1972).

The presumptive E. coli isolates had shown typical biochemical reactions. This confirmed these isolates. All these isolates (from district Gonda) showed typical biochemical reaction which were positive to Indole test, M.R. test, T.S.I. agar test, nitrate reduction test and negative to VP test and H₂S production test. Among 184 E. coli isolates 98.36% were negative to citrate utilization test and 97.82% to urease activity test. Out of 184 isolates of E. coli 179 were motile. They all fermented D-glucose, lactose, manitol. Among 184 isolates of E. coli, 154 (83.69%) isolates, 158(85.86%) isolates and 144 (78.26%) isolates had shown fermentation of sucrose, dulcitol and salicin respectively. Only two isolate fermented adonitol. The result of bio-chemical reaction of E. coli are presented in Table. 2.

The present investigation showed that colibacillosis is a major concern in Gonda district in North Eastern Plain Zone of Uttar Pradesh. To sustain the loss and achieve successful broiler production, it needs investigation about the incidence and pathology of the poultry (broiler) diseases. Such information is also required to take necessary actions for the prevention and control of diseases caused by bacterial pathogens. A thorough knowledge about the epidemiology, pathogenesis and pathology of a particular disease in a prerequisite for proper diagnosis of the malady, as well as for the prevention and control of the disease.