Bacteriological and immunological studies on escherichia Coli Isolates recovered from diarrhoeic and contact apparently healthy sheep with histopathological changes encountered

ABSTRACT

Bacteriolological examination of organ .specimens collected from 18 necropsied local breed sheep, that had history of diarrhoea revealed the isolation of Escherichia coli in 13/18 [72.2%] of the animals, whereas in the faecal samples from diarrhoeic and contact apparently healthy sheep the incidence of E. coli was 42/59 [71.2%] and 17/35 [48.6%] respectively. The identified 72 E. coli isolates were affiliated to 9 .serogroups, O76 [13], O16 [10], O5 [10], O28 [8], O117 [7]. O145 [5], O91 [3], O6 [3], O157 [3] and untypable [10]. All serogroups adhered better on enterocytes cell-model than oil HEp-2 cells, as 53/72 [73.6%] of the isolates adhered with an average of 63.5 +/- 6.2 E. coli enterocyte, whereas on HEp-2 cells the adhesion was .significantly lower [P < 0.05] as 45/72 [62.5%] of the isolates were adherent with an average of 53.9 +/- 6.7 E, coli/ cell. In verotoxin-production assay, 41/72 [56%] of the isolates were verotoxin producer. The OMPs extract of O76, O16 and O5 [which were the most dominant serogroups] were similar and had dense peptide bands between the range of 35k Da to 42 kDa. Lighter peptide bands were also demonstrated in the higher and lower gel ends. Immunoblotting analysis, also showed strong immunogenic protein bands at 35-37kDa and 40 - 42k Da against sera from infected sheep as well us against sera from rabbits immunized with a pool from the extracted OMPs. Using sera from immunized rabbits as adhesion inhibitors in the previously mentioned cell models revealed significant inhibition [P < 0.01] of the adhesion pattern on both previously mentioned cell models. The inhibition averaged 63.7% reduction in the adhesion capacity of enterocyte cell model [23.0 +/- 5.7 E coli/cell], whereas the inhibition of adhesion averaged 52.3% in HEp-2 cell-model [20.2 +/- 3.4 E. coli/cell]. Histopathological findings of necropsied sheep revealed intestine mucosa had coagulative necrosis associated with inflammatory cells infiltrations. Diffuse desquamations and erosions in the mucosa of the villi. Aggrigation of epithelioid and lymphoid cells was also demonstrated in the lamina propria. Lung, interstitial stroma was thickened; bronchioles and alveoli had focal epithelioid stratification, desquamations and ulcerations. Liver was infiltrated by neutrophils, macrophages, lymphocytes and Kupffer cell proliferation. Kidney showed coagulative necrosis of renal tubules. Heart and spleen sections showed also pathological changes which also confirmed the systemic infection with attaching and toxigenic E. coli. It was concluded that OMPs can be used as an effective, highly immunogenic vaccine for controlling infection with E. coli in sheep as well as other animals