Anoxybacillus and Geobacillus biofilms in the dairy industry: effects of surface material, incubation temperature and milk type

摘要

Anoxybacillus (A. flavithermus, A. kamchatkensis subsp. asachharedens, A. caldiproteolyticus and A. tepidamans) and Geobacillus (two strains of G. thermodenitrificans, G. thermoglucosidans and G. vulcanii) isolates and reference strains in whole milk were evaluated for their biofilm production on six different abiotic surfaces. G. thermodenitrificans DSM 465(T) had the highest cell counts (>4 log(10) CFU cm(-2)) on glass and stainless steel (SS) at 55 and 65 degrees C, respectively. G. thermodenitrificans D195 had the highest counts on SS at 55 degrees C (>5 log(10) CFU cm(-2)) and polyvinyl chloride (PVC) at 65 degrees C (>4 log(10) CFU cm(-2)), indicating the existence of strain variation. The ideal surfaces for all strains were SS and glass at 55 degrees C, but their preferences were polystyrene and SS at 65 degrees C. Moreover, Anoxybacillus members were more prone to form biofilms in skim milk than in semi-skim and whole milk, whereas the results were the opposite for Geobacillus. Both the attachment and sporulation of Geobacillus in whole milk was higher than in semi-skim or skim milk. This study proposes that the surface material, temperature and milk type had a cumulative effect on biofilm formation.