The testing of sanitizers efficacy to enterococci adhered on glass surfaces

Abstract

The aim of this work was to test the ability of 6 strains of enterococci to adhere on glass surfaces in environment with different content of milk residues and then to evaluate efficacy of 2 commercial sanitizers (alkaline and acidic) used in milk production. Tested enterococci were isolated from milk, dairy products and from rinse water after sanitation milking machine. Suspension of enterococci (8 log CFU.ml^-1) was prepared in phosphate buffered saline (PBS), PBS with content 0.1% and 1% of skimmed reconstituted milk. Glass plates were immersed into bacterial suspension for 1 h at 37 °C. The number of enterococci adhered on glass surface in PBS achieved an average value 3.47 log CFU.mm^-2, in PBS with 0.1% of milk 2.90 CFU.mm^-2, in PBS with 1% of milk 2.63 CFU.mm^-2. Differences between the tested files were not statistically significant (p >0.05). In the second part of work the glass plates with adhered enterococci were exposed to the effect of alkaline sanitizer (on basis of NaOH and NaClO), respectively acidic sanitizer (on basis of H₃PO₄). Sanitation solutions were prepared and tested according to manufacturer recommendations (concentration 0.25%, contact time 20 min, temperature   20 °C). Alkaline sanitation solution was 100% effective against all tested enterococci regardless to content of milk residues in environment. Acidic sanitation solution was 100% effective only against E. faecalis_D (isolated from rinse water after sanitation). Average value of reduction of enterococci with acidic sanitation solution, which were on glass plates in environment PBS was 2.84 CFU.mm^-2, in PBS with 0.1% of milk was 2.45 CFU.mm^-2 and in PBS with 1% of milk was
2.16 CFU.mm^-2. It can be concluded, that increase of milk residues in environment decrease the adhesion of enterococci on glass surface, but also effectiveness of acidic sanitation solution.