Common occurrence of plasmid DNA and vancomycin resistance in Leuconostoc spp.

Resistance to vancomycin permitted detection, in a culture of Streptococcus cremoris 290PC, of a contaminant gram-positive coccus. Morphological and physiological characteristics indicated that this bacterium was a strain of Leuconostoc sp., designated PO184. This strain contained four plasmid species, which were distinct from those harbored by S. cremoris 290PC. Antibiotic disk susceptibility tests indicated that Leuconostoc sp. strain PO184 was also resistant to sulfathiazole and trimethoprim and susceptible to 17 other antimicrobials. The MIC of vancomycin for this strain was greater than 2,000 micrograms/ml, and resistance did not depend on drug inactivation. Leuconostoc sp. strain PO184 produced a substance which was inhibitory to S. cremoris U134, but not to S. lactis ATCC 11454. Five other leuconostocs produced substances with antibacterial activity. Of 18 strains of Leuconostoc sp., 14 were resistant to at least 500 micrograms of vancomycin per ml, including four L. oenos strains which harbored no plasmid DNA in the 1- to 76-megadalton range. Twelve Leuconostoc sp. strains contained at least one plasmid species in this mass range. These findings are discussed from the physiological, taxonomical, and ecological standpoints and with regard to their potential applications.