Mdt(A), a New Efflux Protein Conferring Multiple Antibiotic Resistance in Lactococcus lactisandEscherichia coli

ABSTRACTThe mdt(A) gene, previously designatedmef214, from Lactococcus lactissubsp.lactisplasmid pK214 encodes a protein [Mdt(A) (multiple drug transporter)] with 12 putative transmembrane segments (TMS) that contain typical motifs conserved among the efflux proteins of the major facilitator superfamily. However, it also has two C-motifs (conserved in the fifth TMS of the antiporters) and a putative ATP-binding site. Expression of the cloned mdt(A) gene decreased susceptibility to macrolides, lincosamides, streptogramins, and tetracyclines in L. lactisand Escherichia coli, but not in Enterococcus faecalisor inStaphylococcus aureus. Glucose-dependent efflux of erythromycin and tetracycline was demonstrated in L. lactisand in E. coli.