Biocidal quaternary ammonium compounds (QACs) are extensively used as disinfectants and in cleaning products, and their active components may enter wastewater, or soil after use. In these environments, these biocides can persist either as intact compounds or as degradation products formed through exposure to UV light, temperature shifts, pH changes, or microbial metabolism. Therefore, it is important to understand whether degradation products retain antibacterial activity or can select for bacteria with reduced biocide susceptibility.
This project focused on degradation products of quaternary ammonium compounds (QACs), specifically benzalkonium chloride with a 12 carbon alkyl chain (BAC 12), the major constituent of ADBAC/BKC (C12 16). Two related QACs, ADBAC/BKC (C12 16) and DDAC, are registered under the EU Biocidal Products Regulation. The study examined how BAC 12 degrades under environmental conditions and whether its transformation products affect two bacterial pathogens, Staphylococcus aureus and Staphylococcus epidermidis, carrying qacA genes associated with QAC tolerance.
In the project four major BAC 12 transformation products were isolated while several other ones were available commercial. The project demonstrated that while BAC 12 and DDAC strongly selected for qacA positive bacteria, none of the tested degradation products produced similar selection pressure. Additionally, Staphylococci were able to metabolize BAC 12 regardless of the qacA status of the cells. Study limitations include testing only one concentration of each transformation product and variability in competition assays. Future work should develop improved, high throughput methods to assess how QAC transformation products influence selection of qacA containing bacteria under environmentally relevant conditions and explore the role of bacterial metabolism in QAC turnover and tolerance development.