CONJUGATIVE R-PLASMIDS IN STREPTOCOCCUS-AGALACTIAE (GROUP-B)

Twenty-one drug-resistant clinical isolates of group B streptococci were investigated for drug-resistance transfer by conjugation. Six strains were resistant to tetracycline, two to chloramphenicol, one to both drugs, and twelve to macrolide antibiotics (erythromycin, oleandomycin and spiramycin), lincomycin, pristinamycin I, and/or chloramphenicol and tetracycline. Ten strains carried R plasmids which were transferable to group B and/or group D recipients by a conjugation-like phenomenon. Six plasmids were transferred at a high frequency (9 × 10-2 to 4 × 10-4) and four, at low frequency (5 × 10-6 to 7 × 10-8). The molecular weight of one plasmid (pIP501) was investigated after transfer into the new hosts and was found to be similar to that carried by the wild strain (19.8 × 106). © 1979.