It's a trap! The development of a versatile drain biofilm model and its susceptibility to disinfection

Pathogens in drain biofilms pose a significant risk for hospital-acquired infection. However, the evidence of product effectiveness in controlling drain biofilm and pathogen dissemination are scarce. A novel in-vitro biofilm model was developed to address the need for a robust, reproduceable and simple testing methodology for disinfection efficacy against a complex drain biofilm.

Identical complex drain biofilms were established simultaneously over 8 days, mimicking a sink trap. Reproducibility of their composition was confirmed by next-generation sequencing. The efficacy of sodium hypochlorite 1000 ppm (NaOCl), sodium dichloroisocyanurate 1000 ppm (NaDCC), non-ionic surfactant (NIS) and peracetic acid 4000 ppm (PAA) was explored, simulating normal sink usage conditions. Bacterial viability and recovery following a series of 15-min treatments were measured in three distinct parts of the drain.

The drain biofilm consisted of 119 mixed species of Gram-positive and -negative bacteria. NaOCl produced a >4 log₁₀ reduction in viability in the drain front section alone, while PAA achieved a >4 log₁₀ reduction in viability in all of the drain sections following three 15-min doses and prevented biofilm regrowth for >4 days. NIS and NaDCC failed to control the biofilm in any drain sections.

Drains are one source of microbial pathogens in healthcare settings. Microbial biofilms are notoriously difficult to eradicate with conventional chemical biocidal products. The development of this reproducible in-vitro drain biofilm model enabled understanding of the impact of biocidal products on biofilm spatial composition and viability in different parts of the drain.