Abstract:

In this study, Oxford cup method was used to screen Lactobacillus plantarum strains with antibacterial effect.
The fermentation supernatants from these strains were either treated with protease or adjusted for pH using NaOH before
being tested for their ability to inhibit the foodborne pathogenic bacteria Escherichia coli O157:H7 and Staphylococcus
aureu. Results showed that organic acid was the major antibacterial compound, yet when adjusted to pH 6.5 the fermentation
supernatants had better inhibition ability against E. coli O157:H7. L. plantarum strain QB3-3 showed antibacterial effect for
up to 96 h. In addition, the antagonistic mechanism of L. plantarum against foodborne pathogens was due to destruction of
the cell structure resulting in morphological changes, leakage of cell contents and finally apoptosis as observed via electron
microscopy.

Key words: Lactobacillus plantarum, organic acid, antibacterial activity