Effects of irradiation and sodium hypochlorite on the micro-organisms attached to a commercial food container

Biofilm formation on various surfaces is a well-known phenomenon and it has caused pollution, health, and safety hazards, and a substantial economic loss. The present study was to evaluate the bactericidal effects of sodium hypochlorite and gamma irradiation on Psudomonas aeruginosa, Listeria innocua, and Escherichia coli biofilm formed on polypropylene (PP), polyethylene (PET), and polycarbonate (PC), which are widely used as food container materials. The bacterial counts of all the micro-organisms tested in the bacterial suspension were decreased linearly by a gamma irradiation and 3 kGy of irradiation decreased the bacterial counts to below the detection limit (<101 cfu/ml). In sodium hypochlorite treated bacterial suspension only a 1 decimal point reduction in bacterial counts was observed until 100 ppm, beyond 100–400 ppm all micro-organisms tested were undetected. The microbial biofilms attached to PP, PE, and PC were very resistant to sodium hypochlorite, showing only 1–3 decimal point reductions even at 400 ppm of the total available chlorine level. In contrast, 3 kGy of gamma irradiation eliminated the micro-organisms attached to PP, PET, and PC with minor exceptions (P. aeruginosa attached to PE and Escherichia coli attached to PC). In conclusion, gamma irradiation was effective for reducing both the bacterial counts in the suspension and biofilms on PP, PET, and PC, while sodium hypochlorite was unable to eliminate the bacterial cells attached to PP, PET, and PC.