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Bactericidal materials gained interest in the health care sector as they are capable of preventing material surfaces from microbial colonization and subsequent spread of infections. However, commercialization of antimicrobial materials requires proof of their efficacy, which is usually done using in vitro methods. The ISO 22196 standard (Japanese test method JIS Z 2801) is a method for measuring the antibacterial activity of daily goods. As it was found reliable for testing the biocidal activity of antimicrobially active materials and surface coatings most of the laboratories participating in this study used this protocol. Therefore, a round robin test for evaluating antimicrobially active biomaterials had to be established. To our knowledge, this is the first report on inaugurating a round robin test for the ISO 22196 / JIS Z 2801. The first round of testing showed that analyses in the different laboratories yielded different results, especially for materials with intermediate antibacterial effects distinctly different efficacies were noted. Scrutinizing the protocols used by the different participants and identifying the factors influencing the test outcomes the approach was unified. Four critical factors influencing the outcome of antibacterial testing were identified in a series of experiments: (1) incubation time, (2) bacteria starting concentration, (3) physiological state of bacteria (stationary or exponential phase of growth), and (4) nutrient concentration. To our knowledge, this is the first time these parameters have been analyzed for their effect on the outcome of testing according to ISO 22196 / JIS Z 2801. In conclusion, to enable assessment of the results obtained it is necessary to evaluate these single parameters in the test protocol carefully. Furthermore, uniform and robust definitions of the terms antibacterial efficacy / activity, bacteriostatic effects, and bactericidal action need to be agreed upon to simplify communication of results and also regulate expectations regarding antimicrobial tests, outcomes, and materials.

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Methane is an important greenhouse gas causing global warming. Compared to carbon dioxide, the effect on global warming is 34 times higher (probably even higher). Methane is released into the atmosphere by various sources. Landfills containing organic material are one important source. Today, the deposition of organic materials in landfills in Germany is forbidden. In other countries, it is still used. A major problem is that old landfills produce high amounts of methane by the decomposition of organic materials in anoxic zones over a long period of time after closure (more than 50 years). If the concentration of methane in the gas released from the landfill is between 40% and 60% (rich gas), the gas is withdrawn by suction and used for the production of electricity and heat by combustion. Below a level of 30% methane (poor gas), this technique is not efficient and methane is normally discharged into the atmosphere. We isolated methaneoxidizing bacteria from various habitats and used them for colonization on mixtures of autoclaved aerated concrete (AAC) and sand-lime brick rubble. Methane-oxidizing bacteria oxidize methane via methanol, formaldehyde, and formate to carbon dioxide and water. In laboratory experiments, methane-oxidizing bacteria were grown successfully on these artificial matrices. After adaption periods, they showed good microbial activity and high methane-oxidation rates. In further experiments, we used this setup for a larger scale field experiment on a landfill site in Bremen. We built up a test field for long-term measurements under realistic conditions. In this paper, we show the results obtained in our laboratory and field experiments and the problems that occurred. Nevertheless , this setup is an interesting option for the recycling of AAC and other building materials by using them as an active biofilter for the removal of methane emission from landfills. K E Y W O R D SAAC, methane oxidation, microorganisms