Peracetic acid disinfectant efficacy against Pseudomonas aeruginosa biofilms on polystyrene surfaces and comparison between methods to measure it

• Peracetic acid is effective against Pseudomonas aeruginosa biofilms on polystyrene surfaces.
• CFUs/absorbance provide good correlation to assess the effectiveness of peracetic acid.
• McFarland test cannot replace to CFU to assess the peracetic acid effect on these biofilms.

In food industry, biofilms are a source of recalcitrant contaminations, being possible sources of public health problems. The aims of this study were evaluate the disinfectant efficacy of peracetic acid against Pseudomonas aeruginosa biofilms grown on polystyrene surfaces, determining the best method to measuring its disinfecting efficacy. PERAsafe® has been used as peracetic acid donor into medium. Direct colony-forming units (CFUs) counts together with two assays based in optical density measurement have been tested. Starting from bacterial suspensions (∼105), the log10 values obtained were 4.34 ± 0.20, 2.60 ± 0.77 and 0.00 for 0.4%, 0.8% and 1.61%, PERAsafe® concentrations, respectively, showing that this compound achieved the 100% killing efficacy against P. aeruginosa biofilms. Comparative study among the selected tests shows similar results between CFUs counts and spectrophotometry, but there are significant differences between direct counting and McFarland test. At concentration of 1.61%, the correlation factors were 0.8998 and 0.7338 when comparing CFU direct counting with microplate absorbance measurements and McFarland turbidity tests, respectively. These results show that measurement on microplates is an effective tool to evaluate the effectiveness of PERAsafe® against P. aeruginosa biofilms, being able to effectively replace the CFUs count in routine tests to determine the sterilization levels on surfaces.