Disinfection Treatment of Heated Scallop-Shell Powder on Biofilm of <i>Escherichia coli</i> ATCC 25922 Surrogated for <i>E. coli</i> O157:H7

Abstract

The ability of heated scallop-shell powder (HSSP) to disinfect Escherichia coli ATCC 25922 biofilm was investigated. On account of its cryotolerance and cell surface characteristics, the E. coli strain is reportedly a useful surrogate for E. coli O157: H7 in surface attachment studies. In this study, an E. coli ATCC 25922 biofilm was formed on a glass plate, and immersed in a slurry of HSSP. Following treatment, the disinfection ability of the HSSP toward the biofilm was non-destructively and quantitatively measured by conductimetric assay. The disinfection efficacy increased with HSSP concentration and treatment time. HSSP treatment (10 mg/mL, pH 12.5) for 20 min completely eliminated biofilm bio activity (approximately 10 8 CFU/cm 2 in non-treated biofilms). In contrast, treatment with NaOH solution at the same pH, and treatment with sodium hypochlorite (200 m g/mL) reduced the activity by approximately one to three log 10 . Fluorescence microscopy confirmed that no viable cells remained on the plate following HSSP treatment (10 mg/mL). Although alkaline and sodium hypochlorite treatments removed cells from the biofilm, under these treatments, many viable cells remained on the plate. To elucidate the mechanism of HSSP activity against E. coli ATCC 25922, the active oxygen generated from the HSSP slurry was examined by chemiluminescence analysis. The luminescence intensity increased with increasing concentration of HSSP slurry. The results suggested that, besides being alkaline, HSSP gen erates active oxygen species with sporicidal activity. Thus, HSSP treatment could also be effective for controlling biofilms of the toxic strain E. coli O157: H7, implicated in food poisoning.