Resistance types in Escherichia coli. II. Transfer of ampicillin resistance.

The ability to transfer resistance traits was investigated in 49 E. coli strains isolated from clinical specimens. The strains were divided into the three groups according to sensitivity to penicillin derivatives. Group 1 contained 8 ampicillin-carbenicillin sensitive (A-s/Ca-s) strains, group 2 contained 16 ampicillin resistent-carbenicillin sensitive (A-r/Ca-s) strains and group 3 contained 25 ampicillin-carbenicillin resistant strains. In group 3, 17 strains could transfer A-resistance (range of transfer frequency was 10(0.0) to 10(-7.5). The 16 strains in group 2 that did not transfer A-resistance more often than mutants arose from the recipient (10(-8.8). The mutants of the recipient selected on A-plates were A-r/Ca-s/cephalothin-resistant, exactly as the strains in group 2. The A-resistance in group 3 was probably based on plasmids, and that of group 2 was based on mobilizable plasmids and/or chromosomal resistance. The frequencies of transfer of sulphonamide-, tetracycline- and streptomycin resistance of the strains in groups 1 and 2 did transfer, were in the same range as the frequencies of transfer in group 3.