Lack of experimental evidence to support mcr-1-positive Escherichia coli strain selection during oral administration of colistin at recommended and higher dose given by gavage in weaned piglets.

In this study, we assessed the selective effect of colistin administered orally to healthy weaned piglets harbouring an intestinal mcr-1-positive Escherichia coli strain. Maximum recommended dose and a higher dose often used in European pig farms were given by gavage. No selection of the mcr-1-positive strain was observed in our controlled conditions, irrespective of the dose. Further investigations in real farming conditions seem necessary.