Impact of virulence genes and pathotypes of intestinal pathogenic Escherichia coli on gastrointestinal lesions in pre- and post-weaning piglets

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Background Pathogenic strains of Escherichia coli ( E. coli ) cause colibacillosis in pre- and post-weaning piglets. Fimbrial and non-fimbrial adhesins, as well as heat-labile and heat-stable enterotoxins, are main virulence factors in enterotoxigenic (ETEC), enteroaggregative (EAEC), enteropathogenic (EPEC) and shigatoxigenic (STEC) pathotypes which cause colidiarrhea or colitoxemia in piglets. Methods Fifty-five piglets submitted for necropsy were examined for gross and histological lesions. E. coli strains were isolated, biochemically confirmed, and tested by PCR for 15 virulence genes (VGs). Statistical analyses used appropriate parametric or non-parametric tests, depending on the distribution. The results with p values less than or equal to 0.05 (p ≤ 0.05) were considered statistically significant. Results Overall, 84.48% of strains carried at least one VG. The occurrence of six VGs - astA , estII , faeG , estI , elt , and paa - was high, with frequencies of 67.24%, 63.97%, 55.18%, 50.00%, 48.27%, and 44.82%, respectively. ETEC predominated (63.79%), while 5.17% of strains carried EPEC or STEC genes; 15.52% were non-specific virotypes, and 15.52% were apathogenic. Lesions were most prominent in the small intestine. The virotype LT:STa:STb:EAST1:PAA:F4 was most common, whereas STa:Stx2:Stx2e was linked to the most severe lesions. Lesions varied depending on the pathotype involved and the VGs expressed. Severity of lesions differed significantly between suckling and weaned piglets (p = 0.0091) and between piglets with and without diarrhea (p = 0.0223), with suckling and diarrheic piglets showing more pronounced pathological changes. More extensive lesions in ETEC were associated with the acquired astA and paa genes. Pathoscores were significantly associated with faeG /F4 (p = 0.0001), eltA /LT (p = 0.0001), estII /STb (p = 0.0001), paa /PAA (p = 0.0002), and astA /EAST1 (p = 0.0029). Discussion and conclusions Strong associations between specific VGs - particularly faeG , eltA , estII , paa , and astA - and higher lesion scores show that VG detection can help predict disease severity and guide interventions. Age-specific interpretation is crucial, as isolates from pre-weaned piglets often carried more VGs and were associated with more severe lesions. This study underscores the value of integrating bacteriological, molecular and histopathological data for accurate diagnosis, especially given the high prevalence of VG-positive and recombinant ETEC strains.

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