To examine the molecular mechanisms of formaldehyde (FA) toxicity under different nutritional environments in urine. Urinary tract infections are most often caused by Escherichia coli strains, which are becoming increasingly antibiotic resistant, and new or adjunct therapies are urgently needed. In an acidic urinary environment, methenamine hippurate (MH) breaks down to FA, which impairs bacterial growth and can be used for urinary tract infections prophylaxis.

A B2 E coli strain (ECOR53) was grown in minimal or nutrient-rich media. Bacterial growth curves were monitored in varying concentrations of FA and the presence of different substrates commonly found in urine: urea, copper, vitamin C, glutathione, and cysteine. Biofilm formation was quantified across a range of FA concentrations in the presence and absence of urea.

Bacteria showed greater tolerance in nutrient-rich media compared to minimal media. Urea reduced FA toxicity, while copper and vitamin C potentiated growth inhibition, particularly in nutrient-limited conditions. The impact of glutathione and cysteine on FA toxicity was dependent on media type. Biofilm assays showed that FA reduced biofilm formation, with urea partially rescuing growth and attachment.

This study determined that FA toxicity was context-dependent, with nutrient-dependent efficacy and modulation by urinary metabolites. Higher concentrations of FA were inversely associated with urea-maintained biofilm formation, while lower concentrations of FA were sufficient to hinder biofilm formation in the absence of urea.