Role of Shiga Toxin-Producing Escherichia coli in Abomasal Lesions of Ruminants: A Pathological and Molecular Study

Abstract

The present study was conducted to investigate the role of Escherichia coli in abomasal lesions of ruminants, with emphasis on pathological, bacteriological, and molecular characterization. A total of 30 ruminant carcasses (cattle, buffalo, sheep, and goats) showing abomasal lesions were examined. Detailed necropsy, histopathology, bacteriological isolation, and polymerase chain reaction (PCR) were performed to identify and characterize E. coli and its virulence genes. Bacteriological examination revealed the presence of Escherichia coli in 20% (6/30) of cases. Identification was confirmed through cultural characteristics, Gram staining, and biochemical tests. Molecular analysis showed that all isolates were positive for the uidA gene, confirming their identity. Further characterization revealed that all isolates harboured the stx1 gene, while 66.67% possessed the hlyA gene, indicating the presence of Shiga toxin-producing E. coli (STEC). However, stx2 and stII genes were not detected in any isolate. Gross and histopathological examination revealed that E. coli-associated lesions were predominantly inflammatory in nature, characterized by abomasitis, congestion, haemorrhage, and infiltration of mononuclear cells. Ulceration was observed in only a few cases, while intestinal lesions such as haemorrhagic enteritis were frequently associated. Liver changes were mild and inconsistent. The findings suggest that E. coli, particularly STEC strains, is associated mainly with inflammatory lesions of the abomasum and intestine. However, its role appears to be opportunistic, acting in conjunction with other predisposing factors rather than as a primary cause of severe ulcerative disease.