Practical test method for biofilms

Biofilms are widely spread and appear on natural materials as well as industrial surfaces, pipes (Figure 1), production facilities and medical equipment and products due to the fact that most bacteria prefer a surface-associated existence. Microbial biofilms (Figure 2) develop when the microorganisms have become irreversibly attached to the surface which takes place after the initial adhesion step when extra-cellular polymers which favor adhesion are produced (Figure 3). The biofilm itself has a structure which is perfused with liquid. In environments which are low on nutrients, substrates are concentrated by polymeric substances. The polymeric matrix also protects the microorganisms which are organized in the biofilm against inactivating environmental conditions. Therefore elimination of biofilms is extremely difficult and removing them is very expensive.

Various antimicrobial strategies have been used and investigated at Fraunhofer IGB to prevent biofilm formation. The interactions between bacteria and material surfaces are evaluated microbiologically according to standardized methods which, in many cases, are insufficient for showing application-specific aspects. At Fraunhofer IGB, in order to evaluate the antimicrobial surfaces, a method has therefore been developed which simulates pipes or devices carrying liquids, in this way showing conditions which are relevant to the practical situation.

With this test method (Figure 4), the test organisms are fed from bioreactors under continuous conditions into one or more measurement chambers (flow cells). Here, the samples are exposed to the incident flow in order to examine the formation of the biofilm under defined conditions.The method has been designed to answer various questions. Samples which have been developed for dental applications, different plastic surfaces with various modifications or even catheters for medical applications have already been investigated.

The method offers many advantages for product development since the growth of biofilms can be controlled by adjusting the flow rate, the composition of the test fluid (e.g. synthetic saliva or urine) and the substrate concentration according to the conditions in the real case. The products can also be tested in terms of preventing bacterial growth during a relatively early stage of development.

With this type of method, it is also conceivable that cleaning strategies for eliminating biofilms can be simulated, cleaning solutions tested and their effects examined.