Robust detection in faeces and in vivo quantification of bacteriophages infecting enterotoxigenic Escherichia coli by quantitative PCR

Highlights • developed a quantitative PCR (qPCR) method specific for the previously isolated ETEC phage ETEP21B and validated in vitro and in vivo.• the qPCR assay exhibited excellent specificity even with non-target phages and in faecal matrices.• in the in vivo PWD model, ETEP21B was detected in faecal samples from all pigs receiving the phage-supplemented diet, confirming successful passage through the gastrointestinal tract.• phage administration did not significantly reduce diarrhoea or shedding compared with challenged controls, the qPCR assay highlighted delivery challenges that ensure further optimisation.