Sensitivity of Escherichia coli after exposure to lincomycin in vitro and in vivo

Exposure of 10 Escherichia coli isolates in vitro to a concentration of lincomycin found in the intestine of swine fed the maximun concentration recommended in feed did not significantly affect sensitivity to 8 antibiotics, 1 nitrofuran, and 1 sulfonamide when compared with sensitivity of E coli isolates not exposed to lincomycin. Changes in sensitivity, on the basis of Kirby-Bauer interpretation, did occasionally occur; however, these alterations were in zonal sizes, which were marginal for designation as sensitive, intermediate, or resistant. These same fluctuations were observed in E coli not exposed to lincomycin. Exposure of E coli to lincomycin in the intestinal tract of swine for 34 days did not alter sensitivity of E coli to tetracycline, dihydrostreptomycin, spectinomycin, lincomycin, or triple sulfa. The results indicated that addition of lincomycin to the feed did not appear to promote resistance transfer in E coli.