Résumé:
Natural inhibitory potential of lactic acid bacteria can be exploited in the bioconservation food and reducing the number of germ contamination and in improving the health of consumers. Therefore, the main objective of this study was to isolate lactic acid bacteria from milk of different animal species produced by traditional farming in mountainous areas in the western region of Algeria and to identify strains with antagonistic effect associated some probiotic properties.
233 Gram-positive isolates, negative catalase and non-spore forming were selected from 58 samples from 22 farms. The antagonistic activity was tested against six indicator strains: Salmonella Typhimurium ATCC 13311, Staphylococcus aureus ATCC 25923, Pseudomenas aeruginosa ATCC 27853, E. coli ATCC 25921, Bacillus subtilis ATCC 21332, Enterococcus faecalis ATCC 51299. Isolates showing an inhibitory power underwent biochemical identification using API 50 CH galleries and API 20 Strep. Characterization of the inhibitor agent was held to hold the bacteriocin producing strains. Isolates that have raised the filled conditions are tested for their in vitro behavior against gastrointestinal tract conditions.
A total of 68 isolates showed an antagonistic activity against at least one test strain. After removing acidity, hydrogen peroxide and phage, only 23 strains kept their inhibitory effect. Biochemical identification was used to identify our 23 isolates as of Lactococcus lactis subsp lactis (4 isolates), Lactococcus lactis subsp. Lactis. biovar .diacetylactis (4 isolates) , Lactococcus lactis subsp.Cremoris (3 isolates) , Streptococcus thermophilus (3 isolates) , Lactobacillus casei (2 isolates ) , Lactobacilllus planetarium (2 isolates) , Leuconostoc lactis ( two isolates ) , Leuconostoc mesenteroides (2 isolate) , Lactobacillus rhamnosus ( 1 isolates) . The molecular technique Rep- PCR confirmed the isolates belonging to different lactic groups.
The bacteriocins produced by these isolates were stable at a treatment of80 °C and 100 °C for 20 min. The study of the kinetics of production inhibiting agent revealed an early production during the exponential growth phase of bacteria (8h to 10h after incubation) with a maximum time between 14h and 16h.
All isolates selected for their effect bacteriocinogenes all, with the exception of Leuconostoc, showed a tolerance of pH 2 and bile salts with good behavior lactobacilli. Provide an important adhesive was also marked for 19 isolates with a smaller rate for 4 Leuconostoc. Resistance to antibiotics was most noticeable at the selected strains with a high rate of survival under anaerobic conditions.
Strains V26, B69, C117 and C177 identified as Lactobacillus can be goods candidate for probiotics applications.
The bacteriocins produced by V17 strain (Lactobacillus casei) and the strain V213 (Lactococcus lactis) showed good heat resistance at 120 ° C for 20 minutes. This property gives them the opportunity to be biopreservatives.
