Inhibitory effects of lactic and malic organic acids on autoinducer type 2 (AI-2) quorum sensing of Escherichia coli O157:H7 and Salmonella Typhimurium

- Pathogens produce auto inducers (AI) for virulence gene expression and survival.
- Escherichia coli and Salmonella strains are tested for AI activity.
- Malic and lactic acids found to inhibit AI activity in pathogen strains.
- Inhibition of auto inducers by organic acids indicates reduction of quorum sensing.

Several organic acid based antimicrobials are reported to reduce bacterial populations but studies showing inhibition of autoinducer-2 (AI-2) activity or quorum sensing are limited. The effect of lactic and malic acids on autoinducer activity of selected strains of Escherichia coli O157:H7 and Salmonella Typhimurium is tested in this study. The strains were screened for AI-2 like activity on spinach and cantaloupe homogenates using autoinducer sensing Vibrio harveyi biosensor strains. The ED 14 strain of E. coli O157:H7 and the SD 10 strain of Salmonella showed highest AI-2 like activity of 55 and 53 Relative Light Units respectively. These two strains were used to evaluate the AI-2 inhibitory activities of lactic and malic acids at 1-4% concentrations (alone or in combinations). Lactic acid at 4.0% had the highest inhibition of 80% on ED 14 E. coli strain while the combination treatment of lactic acid + malic acid at 4.0% each had the highest inhibition of 80% on SD 10 Salmonella strain. Results from the study indicate that the quorum sensing ability of the E. coli O157:H7 and Salmonella Typhimurium strains can be effectively inhibited by antimicrobial organic acids.