Effect of Thymus ciliatus oil-based disinfectant solutions against bio-films formed by Bacillus cereus strains isolated from pasteurized-milk processing lines in Algeria

Abstract

Bacillus cereus is a foodborne pathogen that often persists in dairy environments and is associated with food poisoning and spoilage. This spore-forming bacterium has a high propensity to develop biofilms onto dairy processing equipment and resists to chemical cleaning and disinfecting. This study deals with the in vitro application of thyme oil-based sanitizer solutions against biofilms formed by B. cereus genotypes which persist in pasteurized-milk processing lines. The effect of Thymus ciliatus essential oil on B. cereus planktonic cells and biofilms was assessed. The oil was tested alone and in combination with organic acids or industrial cleaning agents, in order to improve the removal of B. cereus recurrent genotypes. Minimal inhibitory concentrations of planktonic growth (MICs), biofilm formation (MBIC) and biofilm eradication (MBEC) of oil and organic acids were evaluated by microdilution assays. Thyme oil was more effective than organic acids against B. cereus planktonic growth, biofilm formation and established bio-films. High values of MICs were obtained for the three organic acids tested (3.5-4.5%) in comparison with those of essential oil (0.082-0.088%). The combination of oil with other antimicrobials as acetic acid, NaOH or HNO3 improves their effectiveness against B. cereus biofilms. These oil-based sanitizer solutions allow complete B. cereus biofilm eradication and should be an attractive candidate for the control and removal of biofilms in the dairy envi-ronment.