Demonstration of R factors in Bordetella bronchiseptica isolated from pigs.

Transferability of drug resistance in strains of Bordetella bronchiseptica isolated from pigs was examined. These strains were resistant to sulfadimethoxine (SA, more than 1,600 mug/ml), streptomycin (SM, more than 800 mug/ml), and aminobenzyl penicillin (APC, 200 mug/ml). All of them could transfer their drug resistance as one unit to a sensitive strain of Escherichia coli as well as to B. bronchiseptica by mixed cultivation. The transferred SM-SA-APC resistance in the exconjugants of E. coli and B. bronchiseptica was also transmissible by mixed cultivation. But the transfer of triple resistance was not mediated by the cell-free filtrate of the drug-resistant strain of B. bronchiseptica which was used as donor. The triple resistance in the exconjugant E. coli ML1410 was found to be eliminated as a whole by treatment with acriflavin. According to these results, it could be safely concluded that R factors carrying SM-SA-APC resistance were demonstrated in strains of B. bronchiseptica isolated from pigs.