Conjugative acquisition and expression of antibiotic resistance determinants in Listeria spp.

Elements encoding various antibiotic resistances were transferred to Listeria species by conjugation with Streptococcus donor strains. Transfer of a conjugative resistance plasmid, pIP501, and of a conjugative transposon, Tn916, occurred at a frequency of about 10(-6). A previously described conjugative cryptic plasmid, pRYC16, could mobilize a non-conjugative resistance plasmid, pBD10, between Listeria strains. In all cases the resistance determinants were stably-inherited by Listeria and could be retransferred to other members of this genus and to Streptococcus or Erysipelothrix strains by conjugation. Listeria transconjugants expressed resistance to chloramphenicol, tetracycline, erythromycin, kanamycin, tobramycin and amikacin at similar levels to those observed in other plasmid containing Gram-positive organisms.