FIG 2.

Biofilm growth and antibiotic resistance of different GAS serotypes on prefixed H292 epithelial cells or SCC13 keratinocytes. (A and B) Biofilms were formed over 48 h (black) and 72 h (red) at 34°C for the isolates M1T1 (941079), M5 (Manfredo), and M18 (87-282) on prefixed respiratory H292 cells or SCC13 keratinocytes, and biomass (A) and gentamicin killing (B) were measured by determining log₁₀ CFU per milliliter and log₁₀ death (i.e., the total biomass [CFU/ml] − biofilm biomass [CFU/ml] after treatment with 500 μg/ml gentamicin for 3 h), respectively. (C and D) Biofilms of the erythromycin-resistant clinical isolates M11 (GAS-53), M12 (GAS-6), M22 (GAS-8), M73 (GAS-138), M77 (GAS-125), and M89 (GAS-128) were formed over 48 h (black) and 72 h (red) at 34°C on prefixed epithelial H292 cells and evaluated for biomass (C) and gentamicin killing (D). Data are from three separate experiments with three individual biofilms each. Biomass (A and C) is plotted as individual data points (with SD; n = 9), and groups were compared using the Mann-Whitney U test. Gentamicin killing data are means (with SD; n = 3), and groups were compared using Student's t test. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001; ns, nonsignificant difference.