Effect of nosiheptide as a feed additive in chicks on the quantity, duration, prevalence of excretion, and resistance to antibacterial agents of Salmonella typhimurium; on the proportion of Escherichia coli and other coliforms resistant to antibacterial agents; and on their degree and spectrum of resistance.

In the first experiment two groups (B and D) each of ten, 15-day-old chicks were fed for 33 days a diet supplemented with nosiheptide (20 g/t) and 2 groups (A and C) of 10 each a diet without medication. Groups A and B were inoculated with Salmonella typhimurium, var. copenhagen (variant resistant to nalidixic acid of the strain DVR 101) 5 days after treatment was started. At intervals of 2, 4, 6, 8, 10, 12, 14, 21, and 28 days postinoculation the following data were collected: the number of salmonella excreted per gram of feces, their duration and prevalence of excretion, and the proportion of salmonella resistant to 9 antibacterial agents commonly used in human and veterinary medicine, as well as their degree and spectrum of resistance. In the second experiment two groups of 10 chicks each were fed either a basal diet (control group) or a diet supplemented with nosiheptide at 20 g/t (treated group). Immediately before and at the end of treatment, the proportions of fecal coliforms, particularly E. coli, which were resistant to 11 commonly used antibacterial agents, and their degree and spectrum of resistance were determined in the 2 groups of chicks. All the strains isolated before treatment started were E. coli sensitive to the 11 antibacterial agents. The strains isolated at the end of treatment were coliforms otherthan E. coli (40% in the control group, 32% in the treated group) and E. coli (60 and 68%, respectively). Coliforms other than E. coli were, as is usual, resistant to ampicillin and sensitive to the other antibacterial agents. The E. coli strains were either sensitive to all the antibacterial agents or resistant to tetracycline and furazolidone (51.8% in the control group, 34.1% in the treated group), or resistant to furazolidone alone (3.7% in the control group, 5.8% in the treated group). In both experiments these determinations showed no appreciable differences between treated and untreated chicks.