TABLE 3.

Transfer frequencies of vancomycin resistance plasmids from donor strains to recipients carrying the pMG1 plasmid^a

Plasmid from donor cells of E. faecium BM4105SS	Transfer frequency in broth mating with recipient E. faecium BM4105RF carrying:		Transfer frequency in filter mating with recipient E. faecium BM4105RF carrying:
	pMG1	None	pMG1	None
pHTα	<1 × 10−7	1 × 10−4	2 × 10−3	>1 × 100
pHTβ	<1 × 10−7	3 × 10−4	5 × 10−3	>1 × 100
pHTγ	<1 × 10−7	2 × 10−4	3 × 10−3	>1 × 100

^aThe mating experiments were carried out as previously described (14, 20). The mating times of broth mating and filter mating were 3 and 18 h, respectively. The transconjugants were examined after 48 h of incubation of the selective agar plates at 37°C. Throughout the mating experiments, the antibiotic concentration used for the selection of gentamicin- or vancomycin-resistant transconjugants was 100 or 12.5 μ/ml, respectively. The selection of rifampin- and fuscidic acid-resistant recipient strains was carried out at a concentration of 25 μg/ml each, while selection of streptomycin- and spectinomycin-resistant recipient strains was carried out at concentrations of 500 and 250 μg/ml, respectively.