Purpose: To evaluate the potential application of Lactococcus spp and Lactobacillus spp strains to inhibit formation of biofilms by pathogenic bacteria.
Methods: Two Lactococcus (Lc. lactis 69 and 94) and three Lactobacillus (Lb. helveticus 352, Lb. spp 13 and Lb. spp 40), isolated from Brazilian foods, were tested for their ability to produce biofilms capable to inhibit formation of biofilms by Listeria monocytogenes ATTC 7644, Salmonella Typhimurium ATTC 14028 and Escherichia coli O157: H7 ATCC 35150. Tests were carried out with each LAB strain individually or in combinations of one Lactococcus and one Lactobacillus strain. Cultures of LAB (7 log CFU/ml) were transferred to 24-well polystyrene microtiter plates containing MRS broth and incubated at 30ºC. After 48 h, the liquid was removed and each pathogen, grown in TSB (7 log CFU/ml), was added to the wells. After 24, 48 and 72h at 30ºC, the liquids were removed and the cells attached to the wells (biofilms) were suspended by vigorous shaking and enumerated. The statistical significance of results was determined using a t-test (95% confidence interval).
Results: Both Lactococcus strains inhibited the formation of biofilms by all tested pathogens in 24 h, when tested alone or combined with Lactobacillus. Afterwards, the inhibition was time-dependent and varied according to the Lactococcus strain, target pathogen and combination of LAB. After 24 h, the most effective control was against L. monocytogenes, caused by the combination of Lb. helveticus 352 with both Lc. lactis strains.
Significance: Protective biofilms based on these bacteria may be an interesting alternative to control formation of biofilms by bacterial pathogens in the food industry environment.