Isolation and Characterization of a Plasmid fromLactobacillus fermentumConferring Erythromycin Resistance

Lactobacillus fermentumis a lactic acid bacterial species commonly found in the digestive tracts of pigs and rodents and also present in man. We characterized a 5.7-kb plasmid, pLEM3, conferring erythromycin resistance, which was isolated from a porcine strain ofL. fermentum.Plasmid pLEM3 established efficiently inL. fermentum,conferred high-level erythromycin resistance (MIC > 1 mg/ml), and was segregationally stable. A deletion derivative of pLEM3, called pLEM5, was constructed and found to be as genetically stable as the parent. A multiple cloning site was inserted into pLEM5, generating plasmid pLEM7. Nucleotide sequence determination of pLEM5 revealed similarities with known genes. The replicon itself is a member of the pC194 family of rolling circle plasmids. The region responsible for erythromycin resistance was 98.2% identical to theermgene of conjugative transposon Tn1545.