Fig. 4
Effect of P4–9 treatment on the permeability of Ps4 cells to N-Phenyl-1-naphthylamine (NPN). Identical suspensions approximately containing 107 fresh mid-log phase CFU/mL were exposed to P4–9 at twice the peptide MIC for 1 h at 37 °C. Peptide was removed by 3 consecutive washes and cells were allowed to grow in fresh MH medium. At the indicated time points, cells were harvested by centrifugation, suspended at an OD600 of 0.6 in PBS, pH 7.2, and added to the wells of a 96-well black polystyrene flat bottom microplate. Then, NPN was dispensed into each well at a final concentration of 100 μM and fluorescence was recorded in a fluorimeter. For each P4–9 treated suspension, an identical untreated suspension was grown in parallel and subjected to an identical procedure. Results shown are the means ± standard deviation of three independent experiments performed in quadruplicate. Data were analyzed using two-sample t-test and statistical differences were extremely significant (***p < 0.001) or very significant. (**p < 0.01). PBS: vehicle (i.e. cell-free) solution containing 100 μM of NPN