Environmental risks under individual and co-exposure to nisin and cetylpyridinium chloride: From denitrification system disturbance to resistance gene dissemination.

In short-term batch denitrification systems, CPC (0.5–8 mg/L) alone or with nisin (5–80 mg/L) drove total nitrogen removal efficiency down to below 5% at the highest tested concentrations.

• Why it matters: Nisin and cetylpyridinium chloride can co-occur in wastewater treatment, yet their combined effects on nitrogen-removing microbes and the spread of resistance genes remain unclear.
• What they did: Denitrification performance, cytotoxicity, resistance genes, and microbial community composition were measured under individual and co-exposure across multiple nisin and CPC concentrations.
• The result: Co-exposure to 80 mg/L nisin and 8 mg/L CPC increased free resistance genes in water to 9.90 times CK, alongside enrichment of Pseudomonas and positive correlations between mobile genetic elements (intI1, tnpA-04) and multiple resistance genes.

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