Genetic resistance confers protection against clinical severity, intestinal colonization, and mortality in weaned pigs experimentally challenged with pathogenic F18 and F4 InPEC Escherichia coli

Post-weaning colibacillosis (PWC) is a leading cause of morbidity and mortality in nursery pigs, affecting a large proportion of individuals on affected farms, caused by intestinal pathogenic Escherichia coli (E. coli) (InPEC). Its control requires comprehensive control strategies, including measures to address multidrug-resistant E. coli strains and reduced susceptibility to disinfectants. This study assessed the clinical outcome in two pig lines with distinct genetic susceptibility to enterotoxigenic E. coli: a resistant line (Genotype A) and a susceptible line (Genotype B), following experimental challenge with F18 and F4 (K88) pathogenic E. coli strains. At 7 days post-challenge, F18- and F4-challenged genotype B groups had lower body weight (-2.24 kg and -0.77 kg, respectively) and reduced average body temperature (-0.44 °C and -0.28 °C) compared with genotype A pigs. Genotype B pigs exhibited higher lethargy scores and greater loss of body condition compared with genotype A pigs. Following F18 and F4 challenge, genotype B pigs had 6.72-fold (95% CI 2.56—17.60) and 9.06-fold (95% CI 3.95—20.74) higher odds, respectively, of developing a diarrhea score 3 (liquid feces) compared to genotype A pigs. Genotypes A and B pigs shed the challenge strains after DPI 1; however, genotype B pigs challenged with F18 or F4 had increased odds of heavy shedding (score 4) compared with genotype A pigs, with odds ratios of 1.85 (95% CI 0.98—3.49) and 2.86 (95% CI 1.53—5.33), respectively. Marked distal jejunum and mild-to-moderate ileum colonization were observed in F18- and F4-challenged genotype B pigs, respectively, while no bacterial attachment was observed on genotype A pigs. Survival was significantly reduced (p ≤ 0.05) in F18-challenged genotype B pigs and showed a decreasing trend (p = 0.07) in F4-challenged genotype B pigs, while no mortality was observed in genotype A pigs. These findings support the potential use of genetically resistant pigs as a promising strategy to reduce the clinical impact of PWC and warrant further investigation under field conditions.