Biofilms in Flexible Hoses

General Audience Summary:

Many kitchen sinks (and shower heads), have an extendable (pull out) faucet that requires a flexible hose of some length. These hoses are made from different materials and many of the materials leach organic carbon that may facilitate bacterial growth on the surface, referred to as a biofilm, in the hose. The study evaluated different materials commonly used for these flexible hoses and the resultant biofilm growth while simulating realistic use of a kitchen sink or shower. The flexible materials evaluated included polyethylene (PEX) tubing, a silicone based pipe, a pipe with an antibacterial coating containing silver, and two types of polyvinyl chloride (PVC) pipes, one much more expensive than the other. In addition, a non-flexible PEX pipe was evaluated. It’s important to note that the water used in the testing was not chlorinated, which is common for systems that have use groundwater wells for a water source (many public water systems maintain a residual chlorine level in the distribution system).

The results indicated that the PEX tubing (both flexible and non-flexible) as well as the silicone-based pipe leached the lowest amounts of organic carbon (a food source for bacteria) and had the least amount of bacteria growth. However, the community of bacteria that did develop had overall higher numbers of pathogens such as Legionella, a type of bacteria that may cause pneumonia- or flu-like illnesses. The piping with the antibacterial coating initially had lower growth but over-time the coating was lower effective and, after 8 months, it had a similar biofilm to the other flexible pipes tested with the exception of the “cheap’ PVC pipe that had the highest overall number of bacteria present.  Based on their results, the authors suggest that pipe materials should be engineered to leach organic carbon that encourages benign bacterial growth in order to better protect the consumer from harmful pathogen development.

Technical Audience Summary:

Flexible hoses are commonly used in the last one meter (two to three feet) before a fixture at a kitchen sink or shower. Different materials leach more organic carbon which leads to greater biofilm growth in these hoses. The study evaluated different material types commonly used in household plumbing including polyethylene (PEX) (both a non-flexible and flexible pipe), silicone based piping, one with an inorganic silver-ion coating, and two types of polyvinyl chloride (PVC) pipes, one that was much more expensive and included an ash addition in the pipe material. The study examined total organic carbon leaching and biomass growth in the short term and over a longer term (8 months). A BioMig test package was used to quantify the organic carbon migration potential and biomass formation potential. Fluorescence staining was used to calculated total cell concentration (TCC). Total ATP and organic carbon (TOC) in the biofilm was also determined. DNA extraction, qPCR targeting 16S rRNA genes, and 16S rRNA amplicon sequencing was used with statistical analysis to determine the community structure of the biofilm.

The study showed that the PEX non-flexible pipe overall had the least biomass growth while the “cheap’ PVC pipe had the most. After about 8-months, the other four pipe materials (flexible PEX, silicone, silver-ion coated, and ash-PVC had similar biofilm concentrations. Overall, biofilm concentrations increased over time. The community structure varied by both material and time. The authors also found that even though the same source of water was used in all pipes, the community structures did vary between pipe types. They attributed this to the different types and amounts of organic carbon that are leached from the pipes. The pipe materials with the lowest biofilm concentration also tended to have higher amounts of opportunistic pathogens; the four genera found were Legionella, Pseudomonas, Nocardia, and Mycobacterium with Legionella being common to all samples. Six other genera were also found to be common to all samples and included Caulobacter, Bradyhizobium, Sphigomonas, Methyloversatilis, Phenylobacterium and an unclassified genera within Comamonadaceae. Based on their results, the authors suggest that pipe materials should be engineered to leach organic carbon that encourages benign bacterial growth in order to better protect the consumer from opportunistic pathogen development.

Link to Article:

Citation: Proctor, Caitlin R., Marja Gachter, Stefan Kotzsch, Franziska Rolli, Romina Sigrist, Jean-Claude Walser, Frederik Hammes (2016). Biofilms in shower hoses — choice of pipe material influences bacterial growth and communities. Environmental Science: Water Research & Technology, 2016, 2, 670-682.

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