Comparison of gamma irradiation and sodium hypochlorite treatments to inactivate Staphylococcus aureus and Pseudomonas aeruginosa biofilms on stainless steel surfaces

Abstract

Biofilm formation on various surfaces is a well-known phenomenon and it has caused pollution problems, health and safety hazards, and substantial economic loss in many areas including the food industry. In the present study, Gamma irradiation at a dose of 2.0 kGy reduced the bacterial counts of Staphylococcus aureus and Pseudomonas aeruginosa suspensions by 6.7 and >6.5 log CFU/mL, respectively, and 30 ppm of sodium hypochlorite effectively reduced the counts of both bacterial suspensions to below the limit of detection (<2 log CFU/cm(2)). However, in bacterial biofilms attached to stainless steel, gamma irradiation at a dose of 2.0 kGy reduced the counts of S. aureus attached for 1 hr and overnight by >= 5.1 and 5.0 log CFU/cm(2), respectively. Gamma irradiation at a dose of 1.0 kGy reduced the counts of P. aeruginosa counts to below the limit of detection (<2 log CFU/cm(2)). On the contrary, S. aureus and P. aeruginosa cells attached to stainless steel chips were difficult to eliminate using sodium hypochlorite. Four hundred ppm of sodium hypochlorite reduced the counts of S. aureus and P. aeruginosa attached for 1 hr by 2.5 and 3.3 log CFU/cm(2), respectively.