Ability of heated scallop-shell powder to disinfect Staphylococcus aureus biofilm

Abstract

The ability of heated scallop-shell powder (HSSP) to disinfect Staphylococcus aureus biofilm was investigated. A biofilm of S. aureus NBRC 13276 was produced on a glass plate. Scallop-shell powder was exposed to heat treatment at 1000°C in air for 1 h, followed by immersion of the biofilm plate into the HSSP slurry. After treatment, the disinfection ability of the HSSP toward the biofilm was measured nondestructively and quantitatively using a conductometric assay. Disinfection efficacy against S. aureus biofilm increased with HSSP concentration and treatment time. HSSP treatment (10 mg/mL, pH 12.5) of 60 min completely eliminated the biofilm bioactivity (which was approximately 107 CFU/cm2). In contrast, treatment with NaOH solution (pH 12.5)at a pH identical to the HSSP slurry and treatment with sodium hypochlorite (200 μg/mL) caused an approximately four- to five-order reduction in activity. Fluorescence microscopy confirmed that no viable cells remained on the plate after HSSP treatment. Although alkaline and sodium hypochlorite treatments had a stripping effect on the biofilm, many viable cells remained on the plate. HSSP exerted a disinfection effect against S. aureus biofilm that was greater than that provided by alkaline or sodium hypochloritetreatment. This disinfection effect can be effective for controlling bacteria responsiblefor food poisoning. The use of HSSP in food processing is expected to not only be a source of minerals but also prolong the shelf-life of foodstuffs and reduce the pollution resulting from discarded shells.