Effect of ultrasonication on biofilm forming ability of food pathogens in milk model system

Abstract

Biofilm formation in the dairy industry threatens product safety and can lead to food-borne illness. The study investigated the effect of ultrasonication as a nonthermal technique on biofilm formation, hydrophobicity, and injured-cell recovery of common dairy pathogens. Five reference strains (Escherichia coli ATCC 10536, Staphylococcus aureus ATCC 700698, Bacillus cereus ATCC 10876, Bacillus subtilis NCDC 71, Bacillus megaterium NCDC 67) were screened by Congo red plate assay and microtiter plate assay. Specific Biofilm Formation (SBF) values identified B. megaterium (SBF 2.51) and S. aureus (SBF 1.22) as the strongest biofilm-forming strains and selected for further studies. Sterilized skim milk spiked with selected strains was used as sample matrix for ultrasonication experiments. Ultrasonication parameters were standardized at 20 KHz frequency, 750W power 80% amplitude for 20 min. Biofilm formation on stainless steel chips was evaluated using ultrasonicated milk, showing adhered-cell reductions of 2.94 log in S. aureus and 3.47 log in B. megaterium. Cell surface hydrophobicity declined markedly after treatment, indicating reduced adhesion potential. Post-treatment recovery at 37 °C showed an increase in CFU/mL count for both S. aureus and B. megaterium after 12 h, indicating potential recovery under favourable conditions. This study underscores that optimized ultrasonication reduces both planktonic and surface-attached populations, providing a product-friendly, non-thermal approach to enhance quality assurance in dairy processing.