Reduction of Bacillus cereus Biofilms on Stainless Steel Surfaces by Pestalotiopsis sp. Culture Crude Extract

Abstract

Bacillus cereus is capable of forming biofilms on many types of substrata, including stainless steel surfaces. Thus, the presence of B. cereus biofilms in food production facilities is inevitable, and possible food contamination could occur, resulting in product spoilage and deterioration, which would eventually lead to product rejection and financial loss. Pestalotiopsis spp. have been shown to produce a wide range of novel secondary metabolites that have potential medicinal, industrial, and agricultural applications. In this study, B. cereus biofilms were grown on milk pre-soiled stainless steel coupons (20 x 5 mm) for 48 hr at 30{degrees}C in nutrient-depleted medium. After incubation, the biofilms on the coupons were immersed for 15 min in different concentrations (25, 50, or 100 mg/mL) of Pestalotiopsis sp. culture extract at 25{degrees}C or 50{degrees}C. The results showed that the 48-hr old B. cereus biofilms were significantly reduced (p < 0.05) following immersion in all concentrations of extract. Specifically, the 100-mg/mL concentration resulted in 0.18- to 2-log10 and 0.48- to 2.28-log10 reductions at 25{degrees}C and 50{degrees}C, respectively. Secondary metabolites were detected in Pestalotiopsis sp. culture crude extract using thin layer chromatography, indicating that these metabolites have antibiofilm activity. Additionally, fluorescence micrographs displayed decreasing light intensities emitted by the fluorescent dye ethidium bromide at 605 nm, as was also evident from the interactive 3-D surface plots generated using ImageJ 1.52a software, which indicated that the extracellular polymeric substances in the biofilms were disrupted. The current study concluded that secondary metabolites from the extract of Pestalotiopsis sp. have antibiofilm activity and contain possible bioactive agents with activity against many varieties of microbial biofilms.