-Enterococci isolated from a total number of 68 dairy products and 28 human fecal samples were screened for bacteriocin production. The incidence of the bacteriocin-production trait was highest among the cream samples (33.51%), followed by dahi samples (15.55%), raw milk samples (9.51%), Cheddar cheese (9.2%) samples and human feces (4.72%). The isolates showed antilisterial effect besides activity against other lactic acid bacteria. Sixty potent bacteriocin-producing isolates of enterococci were evaluated for the incidence of virulence characters for their safe exploitation. None of the isolates was found to exhibit gelatinase, DNAse or β-hemolysis activity. Furthermore, only 4 bacteriocin-producing isolates among 60 were observed to be vancomycinresistant. It was concluded that bacteriocin-producing Enterococcus strains lacking hemolytic activity and not carrying vancomycin resistance genes may be safely exploited as starter cultures, co-cultures or probiotics. Résumé -Incidence de la virulence d'isolats d'entérocoques produisant une bactériocine.Des entérocoques isolés de 68 produits laitiers et 28 échantillons fécaux humains ont été criblés pour leur production de bactériocine. L'incidence de ce caractère était maximale dans les échantillons de crème (33,51 %), suivis des échantillons de dahi (15,55 %), de lait cru (9,51 %), fèces humains (4,72 %) et fromage Cheddar (9,2 %). Outre leur activité contre les autres bactéries lactiques, les isolats avaient un effet anti-listeria. Soixante isolats d'entérocoques ayant la capacité de production de bactériocine ont été évalués pour l'incidence de leurs caractères de virulence sur leur sécurité d'emploi. Aucun des isolats n'a montré d'activité gélatinase, DNAse et β-hémolyse.

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Adhesion ability of probiotics is the key factor that decides their colonization in the gastrointestinal tract and potential to inhibit pathogens. Therefore, adhesion ability can be considered as a key determinant for probiotic efficacy. Presents study documents the antagonistic activity of viable/untreated, Lithium chloride (LiCl) treated or heat-killed forms of eight probiotic Lactobacillus reuteri strains on the adhesion characteristics of selected pathogens. All strains investigated were able to adhere to Caco-2 cells. L. reuteri strains tested were able to inhibit and displace (P < 0.05) the adhesion of Escherichia coli ATCC25922, Salmonella typhi NCDC113, Listeria monocytogenes ATCC53135, and Enterococcus faecalis NCDC115. The probiotic strain L. reuteri LR6 showed the strongest adhesion and pathogen inhibition ability among the eight L. reuteri strains tested. In addition, the abilities to inhibit and to displace adhered pathogens depended on both the probiotic and the pathogen strains tested suggesting the involvement of various mechanisms. The adhesion and antagonistic potential of the probiotic strains were significantly decreased upon exposure to 5 M LiCl, showing that surface molecules, proteinaceous in nature, are involved. The heat-killed forms of the probiotic L. reuteri strains also inhibited the attachment of selected pathogens to Caco-2 cells. In conclusion, in vitro assays showed that L. reuteri strains, as viable or heat-killed forms, are adherent to Caco-2 cells and are highly antagonistic to pathogens tested in which surface associated proteins play an important role.

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This study was conducted to evaluate the probiotic properties of Lactobacillus reuteri isolated from human infant feces (less than 3 months). Out of thirty-two representative L. reuteri strains isolated from the infant human feces, nine isolates (i.e. LR5, LR6, LR9, LR11, LR19, LR20, LR25, LR26 and LR34) showed survival in acid, bile and simulated stomach-duodenum passage conditions, indicating their high tolerance to gastric juice, duodenal juice and bile environments. The nine isolates did not show strong hydrophobic properties because the percentages of adhesion to the apolar solvent, n-hexadecane, did not exceed 40%, showing that their surfaces were rather hydrophilic. Functionality of these nine probiotic isolates was supported by their antagonistic activity and their ability to deconjugate bile salts. The safety of the nine indigenous L. reuteri isolates was supported by the absence of transferable antibiotic resistance determinants, DNase activity, gelatinase activity and hemolysis. The results obtained so far suggest that the nine strains are resistant to low pH, bile salts and duodenum juice, so they could survive when passing through the upper part of the gastrointestinal tract and fulfill their potential probiotic action in the host organism. According to these results, the L. reuteri strains isolated from human infant feces possess interesting probiotic properties that make them potentially good candidates for probiotics.

Antilisterial efficiency of three bacteriocins, viz, Nisin, Pediocin 34 and Enterocin FH99 was tested individually and in combination against Listeria mononcytogenes ATCC 53135. A greater antibacterial effect was observed when the bacteriocins were combined in pairs, indicating that the use of more than one LAB bacteriocin in combination have a higher antibacterial action than when used individually. Variants of Listeria monocytogenes ATCC 53135 resistant to Nisin, Pediocin 34 and Enterocin FH99 were developed. Bacteriocin cross-resistance of wild type and their corresponding resistant variants were assessed and results showed that resistance to a bacteriocin may extend to other bacteriocins within the same class. Resistance to Pediocin 34 conferred cross resistance to Enterocin FH 99 but not to Nisin. Similarly resistance to Enterocin FH99 conferred cross resistance to Pediocin 34 but not to Nisin. Also, the sensitivity of Nisin, Pediocin 34 and Enterocin FH99 resistant variants of Listeria monocytogenes to low pH, salt, sodium nitrite, and potassium sorbate was assayed in broth and compared to the parental wild-type strain. The Nisin, Pediocin 34 and Enterocin FH99 resistant variants did not have intrinsic resistance to low pH, sodium chloride, potassium sorbate, or sodium nitrite. In no case were the bacteriocin resistant Listeria monocytogenes variants examined were more resistant to inhibitors than the parental strains.

ABSRACTIn this study, a-galactosidase activity and depletion of oligosaccharides by six standard probiotic lactobacillus cultures were evaluated under at incubation times (6, 12, 18, 24, 30 h) in soy milk medium fortified with whey protein concentrate (WPC70) at 1.5%. Reduction of stachyose was higher due to maximum production of a-galactosidase (a-gal) enzyme (133.65 U/mg) by Lactobacillus rhamnosus C6 as compared with the other Lactobacillus cultures and was highest at 30 h of incubation (3.03 mg/100 mL). The results of this study will allow selection of L. rhamnosus C6 culture in soy milk medium supplemented with whey protein concentrate (WPC70), which will enhance growth of Lactobacillus and also reduce whey separation during fermentation process. This culture also showed highest proteolytic activity (381.67 mg serine/mL) by hydrolyzing soy proteins and produce soy bioactive peptides, which have health beneficial activities. PRACTICAL APPLICATIONSL. rhamnosus C6 strain showed maximum a-galactosidase production as well as reduction of oligosaccharides viz. raffinose, stachyose and sucrose mostly present in soy milk. However, Lactobacilus casei NCDC17 also exhibited similar activity during soy milk fermentation. WPC70 fortification enhanced bacterial growth providing nutrition to the bacteria and also increased physiological activity during fermentation in soy milk medium. These two strains can be selected for the development of functional soy foods like soy yoghurt, soy cheese, soy beverages and soy dahi.