Antibacterial Activity of Lactic Acid Bacteria Isolated from Salad Vegetables
To determine the inhibitory capacity of lactic acid bacteria (LAB) due to the action of antagonistic substances, 8 members of the LAB group namely, Lactobacillus brevis, Lactobacillus casei, Lactobacillus cellebiosuis, Lactobacillus delbruesckii, Lactobacillus fermentum, Lactobacillus plantarum, Leuconostoc mesenteroides and Pediococci sp were isolated from the surfaces of five salad vegetables. The cell free supernatants of the selected LAB were able to inhibit the growth of the indicator pathogens used in this study. The largest zone of inhibition (18 mm) was produced by L. delbruesckii, L. fermentum and Pediococci sp. All isolates demonstrated activity and produced diacetyl, hydrogen peroxide and lactic acid to varying degrees and their peak production was found to be during the 48th h. L. cellebiosuis produced the highest amount of diacetyl (2.096 g/l). L. plantarum produced the highest amount of lactic acid (1.801 g/l), while Pediococci sp produced the highest amount of hydrogen peroxide (0.0029 g/l). The sensitivity of the indicator pathogens to these isolates was also investigated by the agar well diffusion method. Resistance was shown to at least two different classes of antibiotics by all the pathogens used.
Keywords: salad vegetables, diacetyl, hydrogen peroxide, lactic acid, agar well diffusion