FIG 4.

Efficacy of two sequential treatments of Ce6-aPDT was evaluated on biofilms of M. catarrhalis 7169 (A) and S. pneumoniae EF3030 (B). NTHi 86-026NP biofilms were omitted from this analysis because the single aPDT treatment was sterilizing. Biofilms were subjected to one round of Ce6-aPDT (1× aPDT at a total light dosage of 90 J/cm² using 10 μM Ce6; solid bars) or immediately retreated with a second round (2× aPDT) using the exact same treatment parameters (hatched bars). Dual treatment completely eradicated all viable biofilm-associated bacteria (≤10 CFU) compared to untreated controls (≥10⁵ CFU) in both organisms. The dashed lines indicate the limit of detection. The data are presented as the means ± SDs, with independent replicates shown. ns, not significant; *, P = 0.0281; ****, P < 0.0001.