Fig 1.

In vitro antibacterial activities of R-thanatin. (A) Time-kill curves of R-thanatin. R-thanatin, ceftazidime, and ampicillin were added to cell cultures containing MRSE to a final concentration of 24 μg/ml, with addition of an equal volume of diluent as a control. Aliquots of each culture were collected at 0.5, 1, 2, 4, and 6 h and were then diluted and inoculated on solid agar. The number of CFU was calculated from the number of colonies growing on plates. The data are shown as mean ± SD values for 3 samples: ∗, P < 0.05; ∗∗, P < 0.01 (versus results for the control). (B) Effects of R-thanatin on growth of bacteria colonies. Compounds were added to cell cultures containing MRSE to a final concentration of 4, 12, or 24 μg/ml R-thanatin or 24 μg/ml ampicillin, with the addition of an equal volume of diluent as a control. Aliquots of each culture were collected at 1 h, diluted, and inoculated on solid agar. The number of CFU was calculated from the number of colonies growing on plates. The data are shown as mean ± SD values for 8 samples: ∗∗, P < 0.01 versus results for the control. (C) Crystal violet staining of biofilms from MRSE grown for 24 h in 96-well plates with 2 μg/ml R-thanatin. R-thanatin at a subinhibitory concentration was added after MRSE cells were cultured for 0, 8, 12, 16, or 20 h. The data are shown as mean ± SD values for 16 samples: ∗, P < 0.05; ∗∗, P < 0.01; ∗∗∗, P < 0.001 (versus results for the control).