FIG. 3.

Natural transformation-mediated transfer of antibiotic resistance determinants in Campylobacter cocultures. (A) Coculture of C. jejuni JB202 (Kan^r) and BQ304 (Tet^r) in MH broth with no antibiotics. The numbers of bacterial cells that were resistant to both kanamycin and tetracycline were determined on plates containing both antibiotics. (B) Effect of washing the inocula on the development of doubly resistant progenies. JB202 and BQ304 were washed with MH broth five times before being inoculated into the coculture. (C) Effect of DNase I treatment on the development of doubly resistant progenies. DNase I was added to the coculture (at a final concentration of 30 μg ml⁻¹) of JB202 and BQ304. (D) Coculture of C. jejuni JB203 (Kan^r) and JB204 (Tet^r) in the absence of DNase I treatment. The Cj1211 gene in both strains was inactivated by insertional mutagenesis. See Table 1 for detailed information on the strains used in this experiment. The results show the means ± standard deviations of data from triplicate samples in a single experiment. Similar patterns of differences were observed in three independent experiments.