Evaluation of Organic Acids, Anti-Salmonella Activities of Lactic Acid Bacteria Isolated from Nigerian Grown Salad Vegetables

Aim: To quantitate lactic and acetic acids produced by lactic acid bacteria (LAB) isolated from Nigerian grown salad vegetables and investigate their in vitro activities against Salmonella enterica ser Typhi.

Study Design: Two group non randomized experimental design.

Place and Duration of Study: Nigerian Institute of Medical Research, Molecular Biology & Biotechnology Division between January 2014 and December 2014.

Methodology: LAB isolated from cabbage, carrot, cucumber and lettuce were identified phenotypically and by partial sequencing of their 16S rRNA genes. Twenty three were investigated for the abilities to produce lactic and acetic acids in growth medium by high performance liquid chromatography following standard protocols. The anti-salmonella activities were performed using acidic and neutralized cell free supernatants (CFS) in agar well diffusion assay according to Clinical Laboratory Standard Institute guidelines. The differences in concentrations between the organic acids were determined by pair t- test at 95% confidence interval.

Results: The isolated LAB were Lactobacillus spp, Weissella spp, Pediococcus spp, Uncultured solibacillus RBL-135 and Enterococcus durans RO2-22. They produced the organic acids at varying degrees with significant difference in concentrations (P< .05); E. durans RO2-22 from lettuce produced 52483 µg/ml and 30439 µg/ml followed by W. confusa FS027 from cabbage producing 20480 µg/ml and 17184µg/ml of lactic and acetic acids respectively. The lowest (134 µg/ml and 517 µg/ml), was produced by L. johnsonii MH8 from lettuce. Three, L. johnsonii MH8, W. confusa SJL 602 from lettuce and W. confusa FS027 from cabbage produced more acetic than lactic acid.

The acidic CFS of W. cibaria, W. confusa showed between 15-16 mm zones of inhibition while P. pentosaceus, P. acidilactici, L. plantarum and L. fermentum showed the least (12- 13 mm).

Conclusion: Most of the selected LAB were able to produce significantly more lactic than acetic acid and their inhibitory activities against the test pathogen was mainly due to low pH.