ABSTRACT
In order to identify lactic acid bacteria [LAB] associated with traditional goat cheeses and to assess their probiotic effect, chemical and microbiological analysis were carried out on seven products collected from different Lebanese regions: Laban [L], Labneh Ambarise[LA], Labneh Serdalli [LS], Jebneh Darfieh [JD], Keshek [K], Shanklish [Sh] and Labneh Darfiyeh [LD]. These samples were analysed for their pH and acidity. The isolation of lactic acid bacteria was achieved using two selective media, namely MRS and M17 agar. Isolated strains were identified according to morphology, Gram staining, catalase and oxydase, ammonia production from arginine, carbon dioxide production from glucose, growth in MRS broth at 10degree C and 45degree C, salt tolerance [2, 4 and 6.5% of NaCl], sugar fermentation with API [Analytical Profile Index] system methods [50CHL and 20Strep]. The probiotic potential of isolates to inhibit pathogenic bacteria [Salmonella, Staphylococcus aureus and E. coli], their survival at different pH [1, 2, 3 and 7.2], the time needed to reach acidification end point in full and skimmed milk were assessed. Labneh Ambarise and Labneh Darfiyeh had an average pH of 4+/-0.5 and a titratable acidity of 2%+/-0.1 [w/w], while the average pH and titrable acidity of Darfiyeh cheese were 5.22 and 0.62 respectively. The presence of LAB in one year old samples preserved in olive oil could not be detected. Twenty five strains were isolated and identified from different samples, where nine of them belong to Lactobacillus plantarum [L2, Sh2, K2, K3, K4, K5, LS1, LS3 and LS4], three are Lactobacillus paracasei spp. paracasei [Sh3, LS2 and LS5] and five are Leuconostoc mesenteroides spp. dextranicum 2 [JD1, JD2, JD3, JD4 and JD5]; four colonies are suspected to be Lactobacillus casei [L1, Sh4, K1 and K6] and four others are probably yeasts [L3, L4, L5 and L6]. Identified strains showed a capacity to produce antimicrobial substances with maximum inhibition diameters of 20 mm against Salmonella [K1, Sh4, LS1 and JD1], 21 mm and 19 mm for L2 against Escherichia coli and Staphylococcus aureus, respectively. The microorganisms survival rate in simulated gastric juice [SGJ] varied between 50% and 93% at pH 3 [Sh3, K2, LS2, LS5, JD1 and JD3]. Their growth was inhibited at pH 1 [0.05% to 0.08%]; only JD1 and JD3 showed more then 50% of viability at pH 2. The time needed for milk acidification had an average of more than 10 h exceeding the time required by yogurt starter cultures [5 h]. The Jebneh Darfieh sample, rich in Leuconostoc mesenteroides, showed the most interesting characteristics of cell viability at pH 2 [50% for JD1 and JD2] and a maximum of 20 mm of inhibition against Salmonella. It could be used as a natural source of probiotic. The isolates of the samples Laban, Shanklish, Keshek and Labneh Serdalli [L. plantarum and L. paracasei mainly] were more sensitive to high acidity [pH=2], but showed good antimicrobial activity against pathogens. Microencapsulation is probably required to protect them from harsh conditions. Further tests are needed to determine the exact identity of some strains and the nature of secreted substances responsible of the probiotic effects
ABSTRACT
penicillin tolerance was elicited in 12 of 30 stratns of vitidans streptococci isolated from the mouths of 32 healthy subject Streptococcus sanguis were the organisms most frequently tolerant but the property was also common among isolates of S. mutans, and S. mitior, S. Salivarius was rarely tolerant. When incubated with penicillin at 5 chi MIC, both tolerant and sensitive strains of oral streptococci declined in number less rapidly than S. pyogenes