Testing the resistance of
automobile air conditioning systems to biofilm formation (microbial odor formation)
The microbiological contamination of air conditioning (AC) evaporators in vehicles can lead to considerable unpleasant odor pollution in the vehicle interior on account of microbial metabolites. Vehicle manufacturers tackle this problem by using coating systems with anti-adhesive or microbicidal properties and modifying the design of the evaporators, thus preventing and/or impeding the colonization and growth of microorganisms on the relevant heat exchange surfaces. To validate these measures, a real-life “Microbiological Contamination Test for Evaporators in Vehicle Air Conditioning Systems” was commissioned by the automobile manufacturers in VDA [German Automotive Industry Association] working group 2.4 (Air Conditioning), which culminated in a testing directive and allowed testing to take place with reproducible results. In addition to a yeast, the test organisms used consisted of two species of bacteria that had been identified during investigations of vehicle AC systems conducted worldwide as microorganisms that are typically predominant in evaporator flora.
Investigation of biofilm formation and removal in static and dynamic bioreactors
Whenever materials or coating systems used for technical purposes have to meet stringent hygiene criteria or demands relating to corrosion resistance, the first factor that must be investigated from a microbiological viewpoint is the susceptibility of the relevant surfaces to microbial growth (biofilm formation). When conducting microbiological contamination tests in bioreactors, the development of biofilm on exposed test samples is characterized and quantified using classic and modern analytical methods (determining living cell counts using MPN technology, microbial population analysis using protein fingerprinting and MALDI-TOF, atomic force and fluorescence microscopy, microcalorimetry). Suitable test organisms are kept in the company’s collection of cultures. Antimicrobial surfaces (functionalized for example using quorum quenching or anti-adhesive coatings) and microbicidal preventive measures (e.g. chlorination or doping with zinc or silver) can be tested and validated in the same way.
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