ABSTRACT
Probiotics have been consumed in fermented dairy products such as yoghurt. This study was carried out to assess the probiotic potential of Lactobacillus species isolated from yoghurt samples in Benin City. Seven (7) different yoghurt samples were purchased at Stop to Shop Mall in Ugbowo, Benin City, Edo State. Isolation and identification of bacteriawas carried out on DeMann Rogosa and Sharpe (MRS) medium by using the pour plate technique. Inoculated Petri dishes were then incubated for 48hr for the development of colonies. After incubation, Lactobacillus species were identified using cultural, morphological and biochemical tests. The identified Lactobacillus species from the yoghurt samples were then subjectedto acid tolerance (pH 3) and bile salt tolerance tests (0.3%) for a duration of 3 hr. The antagonistic activity of the isolates were determined against selected pathogenic bacteria namely; Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Pseudomonas aeruginosa using the agar well-diffusion technique. Four Lactobacillus species isolated (LB 1, LB 2, LB 3 and LB 4) from the yoghurt samples were selected for the acid and bile salt tolerance tests. Results revealed that after 3 hr of incubation in MRS agar at pH 3, Lactobacillus count ranged from 1.50×107 cfu/ml (LB4) - 8.00×107 cfu/ml (LB1) with a survival rate of 6.4% (LB4) - 30.8% (LB1) respectively. Similarly, in the MRS medium supplemented with 0.3% bile, Lactobacillus count ranged from 0.3×106 cfu/ml (LB4) - 1.6×106 cfu/ml with a survival rate of 1.2%(LB4) - 28.6% (LB2) respectively. The antagonistic results of the Lactobacillus isolates against pathogenic bacteria revealed the range of zone of inhibition, Staphylococcus aureus (11.50±1.50 - 16.50±3.50mm), Bacillus subtilis (11.00±0.00 -13.50±0.50mm), Pseudomonas aeruginosa (12.50±0.50 - 16.00±0.00), Escherichia coli (11.00±0.00 - 14.50±0.50mm). The highest antagonistic activity of the isolates against Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus subtilis, Escherichia coli were exhibited by LB1(16.50±3.50mm), LB1(16.00±0.00mm), LB1(13.50±0.50mm) and LB1(14.50±0.50mm). The results from this study generally revealed that the dairy products such as yoghurt contain probiotic microorganisms which could be of medical importance due to their observed antagonistic characteristics against potential pathogenic microorganisms in humans.
