Mechanism of Chloramphenicol Resistance in Group B Streptococci (Streptococcus agalactiae)

One hundred group B Streptococci (Streptococcus agalactiae) isolated from clinical specimens investiaged for serotyping and drug susceptibility. Of these, 3 donor strains designated BTO 21, BTO 22 and BTO 23, transferred chloramphenicol (CP) resistance marker and chloramphenicol acetyltransferase (CAT) producing activity by conjugation into group B Streptococci recipient strains. The CP resistance appeared to be due to the presence of CAT mediated by a plasmid. The molecular weight of a streptococcal conjugative R plasmaid, designanted pBTO 22, was investigated after transfer into recipient strains and was found to be similar to that the wild-type group B Streptococcus host (19-20×106). The products of chloramphenicol acetylation obtained by inactivation were identified as 1- acetoxy, 3-acetoxy and 1, 3-diacetoxy derivatives, respectively, by thin-layer chromatography.