Combination of natural antimicrobials and sodium dodecyl sulfate for disruption of biofilms formed by contaminant bacteria isolated from sugarcane mills

•Nisin and carvacrol work synergistically with SDS against some LAB.•Carvacrol at 500 mg/L plus SDS at 75 mg/L can remove up to 82.35% of preformed bacterial biomass.•Metabolic activity of biofilms was inhibited by > 80% with the combination of 500 mg/L carvacrol and 75 mg/L SDS.•This combination could be used as a formulation for cleaning tanks, pipes, and heat exchangers.

Bacterial contamination is found during ethanol production in the form of biofilms, which can decrease ethanol yield by 30%. Carvacrol, nisin, and hops extract, alone and in combination with SDS, were tested against planktonic and preformed biofilms of Lactobacillus fermentum, Lactobacillus plantarum, and/or Leuconostoc mesenteroides. MICs of carvacrol, nisin, hops extract and SDS were 250, 30, 5 and 37.5 mg/L, respectively, against all bacteria. Synergism between SDS and carvacrol (FICindex = 0.125), and SDS and nisin (FICindex = 0.25) was also found against all bacteria. Bacterial viability within biofilms and removal of biomass were indirectly measured using MTT and crystal violet methods, respectively. Metabolic activity of biofilms was inhibited up to 92% with nisin + SDS, while carvacrol + SDS could remove 82% of the biomass. Thus, combined use of these antimicrobials and SDS may provide an effective method for cleaning equipment of ethanol plants and prevent formation of biofilms.