Figure 3.

The effect of black carbon (BC) on biofilm tolerance to antibiotics. Biofilms of S. aureus SH1000 (a–c), Newman (d–f), and USA300 (g–i), and S. pneumoniae PR201 (j) were cultured in the presence or absence of 100 μg/ml BC for 24 h. Planktonic and loosely‐adhered bacteria were then removed and biofilms were either incubated with 3 ml of an antibiotic‐containing medium or control medium for 3 h at 37°C in 5% (v/v) CO₂. For S. aureus, oxacillin (50 mg/ml in BHI + 2% (w/v) NaCl), daptomycin (256 µg/ml in BHI + 50 µg/ml CaCl₂) and tetracycline (512 µg/ml in BHI) were used. For S. pneumoniae PR201, penicillin G (1 µg/ml) was used in BHI. Planktonic and loosely‐adhered cells were then removed and biofilm bacteria quantified. n ≥ 3. Error bars represent ± 1 SEM. Significance was determined by unpaired t‐tests.