Microbiological requirements for lubricants in contact with drinking water

Experimental set-up for Pseudomonas aeruginosa propagation

Microbiological problems in water supply systems could sometimes be attributed to the installed fittings and to the lubricants they contain. A practically relevant test specification for these lubricants should be developed in this project.

It has been established multiple times that the root cause of some microbiological problems, particularly the detection of coliform bacteria and elevated colony counts found on fittings in water supply systems, lies in the lubricants used within these fittings. Water supply fittings that contain lubricants, for example, are shut-off valves. The lubricants in the fitting are a required design element and so it is impossible to entirely dispense with lubricants.

The German Environment Agency defines requirements on lubricants are defined in its lubricant guideline, although this does not include any quantitative microbiological requirements. The aim of the TZW project was to develop a test specification that is practically relevant to this situation so as to estimate the potential of a lubricant to cause microbiological problems.

Pseudomonas aeruginosa was selected as a model organism to develop a microbiological lab test method because this organism can also multiply at very low substrate concentrations and it is easily to determine using lab equipment.

An investigation into the propagation of Pseudomonas aeruginosa in direct contact with the lubricants in batch trials over 14 days and subsequent quantification of the surface growth by rinsing three times, resulting in a feasible test method that also has practical relevance.

This procedure gave meaningful results that ranged from less than 1 to more than 4 log phases compared with the negative control. The method displayed good reproducibility. As possible requirements, a propagation boost of less than 1 log phase was required compared with the negative control and a concentration in the third reflushing step of less than 1000 CFU/ml.

There is still no regulatory implementation.


TZW Volume 65, 2014, p. 95-101