Bactericidal efficacy of some commercial disinfectants on biofilm on stainless steel surfaces of food equipment

Abstract

This study aimed to determine the most effective concentration of the most effective disinfectant for use in the disinfection of food processing equipment to remove Gram positive and/or Gram negative bacterial biofilms. Eight disinfectants [10% NaOH (sodium hydroxide), 70% C2H5OH (ethanol), 30% H2O2 (hydrogen peroxide), 4–6% NaOCl (sodium hypochlorite), C3H7OH (isopropyl alcohol), mixtures of H2O2 and NaOCl, H2O2 and C2H5OH, H2O2 and C3H7OH] were used against bacteria that commonly contaminate food-processing equipment and cause food poisoning, namely: Bacillus subtilis and Staphylococcus aureus (Gram positive bacteria), and Escherichia coli, Pseudomonas aeruginosa and Salmonella typhi (Gram negative bacteria). The bacteria were grown on stainless steel slides to allow biofilm formation. The most effective disinfectant on all tested bacteria was found to be H2O2. Spread plate enumeration (CFU/ml) showed that the difference in the number of cells between untreated and treated samples decreased from 7 log units to 3, and from 7 log units to 0 at minimal inhibitory concentration (MIC) for P. aeruginosa and S. aureus, respectively. The results were confirmed by scanning electron microscopy (SEM) of untreated and treated biofilms of the two organisms at MIC and minimal bactericidal concentration (MBC) of H2O2. The MICs were equal to MBCs for all tested bacteria (Gram positive and negative) except for Pseudomonas (Gram negative), with values of 0.23 and 0.47% for MIC and MBC, respectively—the lowest concentration value of all tested bacteria. This study revealed that the MBC of H2O2 was completely effective and could remove all viable bacterial cells in the bacterial biofilm.