The main topic of this paper was to study the effect of ultrasound-attenuation (US) on the surface properties of propionibacteria (Acidipropionibacterium jensenii DSM 20535 and Propionibacterium freudenreichii DSM 20271). A preliminary screening was done by using different power levels (40 and 60%) and treatment times (4, 6, and 8 min); immediately after sonication, acidification and viable count were tested. The best combinations to avoid post-acidification after 6 h were the following: A. jensenii DSM 20535: power, 40%; time, 8 min; P. freudenreichii subsp. freudenreichii DSM 20271: power, 60%; time, 4 min. Moreover, the effect of US on the growth patterns, surface properties (biofilm formation and hydrophobicity), resistance to some selected antibiotics, and release of intracellular components was evaluated; the experiments were done immediately after the treatment. US-treatment improved the stability of biofilm after 5-7 days, caused an increase of hydrophobicity (from 15 to 27%) immediately after sonication, and determined an increase of cell permeability, as suggested by the release of intracellular components within 24 h and by the increased sensitivity to some antibiotics. This paper is the first report on US-attenuation on propionibacteria and could the background for future researches to modulate the surface properties of these microorganisms.
Keywords: Attenuation; Permeability; Propionibacteria; Surface properties; Ultrasound.
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