17-1

N. Zelver, Center for Biofilm Engineering, Montana State University, Bozeman, MT 59717-3980 and R. JORDAN.

Biofilms are highly resistant to antimicrobial agents or technologies that dislodge the polymeric organic matrix from the surface. Studies have shown that an equivalent disinfection of biofilm bacteria compared to suspended bacteria may require antimicrobial applications of 100 to 1,000 times the normal dose. Thus, biofilm related problems such as contamination of food or food processing equipment are extremely difficult to control. Even rigorous sterilization of food process equipment can leave behind biofilm organic residue that is prone to rapid recolonization by biofilm bacteria. Fundamental theories and supporting evidence will be presented describing three mechanisms of biofilm resistance to antimicrobials. These resistance mechanisms consist of: (1) transport limitations that limit the ability for antimicrobials to penetrate the biofilm (2) physiological heterogeneity within a biofilm resulting in areas of organisms with antimicrobial resistant phenotypes and (3) adaptive stress response. To develop biofilm antimicrobial strategies, these resistance mechanisms must be considered. Compounding the problem of biofilm resistance to antimicrobials is the lack of standard methods for evaluating the efficacy of antimicrobials in controlling biofilm. Biofilm resistance mechanisms must be addressed in developing standard antimicrobial screening tests for controlling biofilm. Development of a tier 1 biofilm antimicrobial screening test will be discussed as well as strategies for scaling up the tier 1 test to specific applications such as food processing. The strategy for tier 1 testing includes analyses of three parameters that are critical to controlling biofilm: (1) disinfection of the biofilm organisms (2) removal of the biofilm from the contaminated surface and (3) regrowth of biofilm organisms following application of the antimicrobial.