TABLE 3.

Conjugal transfer of resistance genes erm(B) and tet(M) from S. pyogenes donors displaying different P/G combinations to the same susceptible S. pyogenes recipient

Donor strainaDrug selectionbTransfer frequencyTransconjugant results
ERY and TET resistance genotypesMIC (μg/ml) of:Size (kb) of new DNA insertionsc
ERYTET
A-3ERY1.7 × 10−5 erm(B) tet(M)>1280.25ca. 50
B-83ERY1.9 × 10−7 erm(B) tet(M)>1283221
B-83TETNDTd
C-105ERY5.8 × 10−9 erm(B) tet(M)>1283223
C-105TET2.1 × 10−10 erm(B) tet(M)>1283223
D-112ERY2.2 × 10−8 erm(B) tet(M)>1280.2523
E-115ERY1.8 × 10−5 erm(B) tet(M)>1280.25NDe
F-119ERYNDT
G-124ERYNDT
  • a The letter (A to G) of each strain label refers to the designation of individual P/G combinations described in Table 2.

  • b ERY, erythromycin; TET, tetracycline. For the selection of transconjugants, erythromycin and tetracycline were used at concentrations of 1 and 10 μg/ml, respectively.

  • c As determined by SmaI PFGE and hybridization analysis.

  • d NDT, no detectable transfer under conditions used.

  • e ND, not determined.