Antibacterial Activities of Lactic Acid Bacteria Isolated from Selected Vegetables Grown in Nigeria: A Preliminary Report

Members of lactic acid bacteria (LAB) are known probiotics and have been reported to have antimicrobial properties. Although various researchers have documented the isolation of these bacteria from fruits and vegetables, studies on LAB associated with lettuce, cucumber and cabbage are limited and non-existing in Nigeria. This study was designed to assess lettuce, cucumber and cabbage as potential sources of LAB and investigate the actions of their bacterial cell supernatants (BCS) on some pathogenic bacteria. Using standard microbiological methods, isolated LAB were identified to species level with API 50 CH kits (Biomerieux, France). Cell free supernatants (CFS) from de Man Rogosa Sharpe (MRS) broth cultures of the LAB strains were used to challenge Pseudomonas aeruginosa ATCC 27853, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 12900 and Proteus penneri ATCC 13315 by agar well diffusion method. The control consisted of the sterile MRS broth subjected to the same growth conditions as LAB broth cultures. A total of four lactic acid bacteria were isolated as follows: Pediococcus pentosaceus 2 from cucumber, Lactobacillus cellobiosus from cabbage, Lactobacillus salivarius and Lactobacillus plantarum 1 from lettuce. Pediococcus pentosaceus 2 and L. salivarius showed inhibitory effects on all the standard strains tested while L. plantarum 1 showed no inhibitory activity against E. faecalis and E. coli. Lactobacillus cellobiosus showed inhibition against all except P. penneri. Although, the molecular characterisation and probiotic potentials of these LAB strains are being investigated in an on-going study, we presumed these vegetables are prospective sources of the bacteria in Nigeria and therefore the need to extensively investigate the vegetables and other related vegetables becomes imperative.