Medical implications of macrolide resistance and its relationship to the use of tylosin in animal feeds.

Staphylococcus aureus strains isolated from human patients were tested for susceptibility to erythromycin and certain related antibiotics by the disc method. The incidence of resistance to erythromycin has remained relatively constant at less thatn 20 percent. Only four percent of erythromycin-resistant human clinical isolates were cross-resistant to tylosin. Oral administration to humans of tylosin or erythromycin did not cause an imbalance in the gram-negative Enterobacteriaceae nor did it cause the selection of resistance factors. It is concluded that, from the human medical standpoint, the use of tylosin in animal feeds does not present any threat to human health.