title: Synergistic bactericidal action of phytic acid and sodium chloride against Escherichia coli O157:H7 cells protected by a biofilm.
abstract: The food industry must prevent the build-up of strong Escherichia coli O157:H7 biofilms in food processing environments. The present study examined the bactericidal action of phytic acid (PA), a natural extract from rice bran and the hulls/peels of legumes, against E. coli O157:H7 biofilms. The synergistic bactericidal effects of PA plus sodium chloride (NaCl) were also examined. E. coli O157:H7 biofilms were allowed for form on stainless steel coupons by culture in both rich (tryptic soy broth, TSB) and minimal (M9) medium at 22°C for 6days. Bacterial cells within biofilms grown in M9 medium were significantly more resistant to PA than those grown in TSB (p<0.05); thus M9 medium was selected for further experiments. The anti-biofilm effect of PA was significantly increased by addition of NaCl (2-4%) (p<0.05); indeed, the combination of 0.4% PA plus 3-4% NaCl completely inactivated E. coli O157:H7 biofilms without recovery (a>6.5logCFU/cm(2) reduction). Neither PA nor NaCl alone were this effective (PA, 1.6-2.7logCFU/cm(2) reduction; NaCl, <0.5logCFU/cm(2) reduction). Confocal laser scanning microscopy images of propidium iodide-treated cells showed that PA (0.4%) plus NaCl (2-4%) had marked membrane permeabilizing effects. These results suggest that a sanitizer that combines these two naturally occurring antimicrobial agents may be useful to food safety managers who encounter thick biofilm formation in food processing environments.
authors.affiliation: Department of Biotechnology, College of Life Sciences and Biotechnology, Korea University, Seoul 02841, Republic of Korea.
authors.forename: Nam Hee
authors.initials: NH
authors.lastname: Kim
authors.affiliation: Department of Biotechnology, College of Life Sciences and Biotechnology, Korea University, Seoul 02841, Republic of Korea. Electronic address: rheems@korea.ac.kr.
authors.forename: Min Suk
authors.initials: MS
authors.lastname: Rhee
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects; D015169:Colony Count, Microbial; D019453:Escherichia coli O157 / Q000187:drug effects*; D005511:Food Handling; D005516:Food Microbiology; D010833:Phytic Acid / Q000494:pharmacology*; D012965:Sodium Chloride / Q000494:pharmacology*; D013193:Stainless Steel / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D013193:Stainless Steel; D012965:Sodium Chloride; D010833:Phytic Acid
keywords: Biofilm; Control; Escherichia coli O157:H7; Phytic acid; Sodium chloride