Conjugative transfer of multiple antibiotic resistance markers in Streptococcus pneumoniae

Abstract

Twenty antibiotic-resistant isolates of S. pneumoniae were investigated for conjugative transfer of their drug resistance markers into streptococcal (groups B and D) and pneumococcal (encapsulated and non-encapsulated) recipients. Of these, 7 wild-type donor pneumococci transferred all their resistance markers (except Pc [penicillin], Su [sulfonamide], and Tp [trimethoprim]) into group D Streptococcus and non-encapsulated S. pneumoniae recipients at a low frequency (10-5 to 10-6). The resistance markers transferred were Tc (tetracycline); Tc and Cm (chloramphenicol); Tc and MLS (macrolides, lincosamides, and streptogramin B); Tc, MLS, Km (kanamycin), and Cm. The transconjugants obtained retransferred their resistance markers into appropriate streptococcal or pneumococcal, recipients or both. The resistance markers of streptococcal transconjugants could not be cured by chemical agents. All attempts to detect extrachromosomal deoxyribonucleic acid from pneumococcal or streptococcal transconjugants were unsuccessful. The molecular weight of a streptococcal conjugative R plasmid (pIP501) was investigated after transfer into the non-encapsulated S. pneumoniae recipient and was found to be similar to that of the wild-type group B Streptococcus host (20 x 106).