Sequence and genetic organization of the 19.3-kb erythromycin- and dalfopristin-resistance plasmid pLME300 from Lactobacillus fermentum ROT1

Lactobacillus fermentum ROT1 was isolated from a raw milk dairy product. It is resistant to novobiocin, tetracycline, erythromycin and dalfopristin. A chromosomal tetracycline-resistance determinant was identified as tetM. A 19,398-bp plasmid (pLME300), present in several erythromycin-resistant strains of Lb. fermentum, was isolated from strain ROT1 and completely sequenced. Based on putative open reading frames, pLME300 contains at least four different functional regions. In region I, ORF1 shows high homologies to replication proteins of different theta-replicating plasmids. In addition, a tandem repeat of a 22-bp sequence appears 4.5 times. In region II, ORF3 may code for a methylase, and ORF4 has homologies to Mrr restriction system proteins of Deinococcus radiodurans and Escherichia coli suggesting a restriction-modification system. Region III harbours antibiotic-resistance genes, coding for a macrolide-lincosamide-streptogramin B (MLS) methylase Erm(LF) and the streptogramin A acetyltransferase Vat(E), which is identical to Vat(E) from Enterococcus faecium. Furthermore, region III shows a 91% nucleotide sequence identity to an erm-vat linkage of E. faecium. Region IV carries ORFs that appear to be involved in plasmid mobilization as characterized by a putative origin of transfer and a mobilization protein. pLME300 is the largest completely sequenced multi-resistance plasmid isolated from any Lactobacillus strain so far.