Does It Have To Be F4 Positive To Be Significant?

F4 positive isolates (such as O149:K91:F4) can certainly be the cause of scours in piglets and weaned pigs , however, F4 positive isolates are less commonly isolated in cases submitted to our laboratory for neonatal scours, likely because the F4 pilus is included as an antigen in commercial E. coli bacterins so prevalence is reduced through the use of a standar d pre - farrow vaccination regime. Non - hemolytic, F4 negative isolates may still be ETEC strains and have toxin genes. These strains may not be included in commercially available products and have been shown to cause neonatal scours.