Incomplete cross resistance against ionophores in Enterococcus faecium andEnterococcus faecalis strains from pigs and poultry

Thirty-two Enterococcus faecium strains and 33 Enterococcus faecalis strain s were tested for their susceptibility to the ionophore antibiotics salinom ycin, narasin, monensin, and lasalocid, Enterococcal strains originated fro m poultry in which these products are in use as coccidiostats, and from pig s in which these products are allowed as growth promoters. Resistance again st salinomycin and narasin in enterococci was frequent among poultry strain s, whereas in pig strains, resistance was less common. No resistance was fo und against monensin and lasalocid, Full cross resistance between salinomyc in and narasin was evident. There was no cross resistance between these two ionophores and monensin and lasalocid.