FIG 1.

In a modified time-kill assay done in LB aerobic culture, the addition of 1.5 mM to 15 mM nitrite blocked the bactericidal activity of the aminoglycosides tobramycin (A) and gentamicin (B). Brackets indicate differences with P values of <0.05 by one-way ANOVA followed by Tukey testing (n = 4 for panel A and 3 for panel B). (C) Nitrite increases the MBC-biofilm for gentamicin. At 48 h, there was robust biofilm growth as seen by crystal violet staining (inset). Biofilms were treated for 2 h with gentamicin ± 75 mM nitrite. For control biofilms, the MBC-biofilm was 256 μg/ml, while for nitrite-treated biofilms, the MBC-biofilm was >1,024 μg/ml (n = 4; data from a representative assay are shown).