Abstract

Several lactic acid bacteria strains were screened for the production of antibacterial substances active against some pathogenic bacteria. The inhibitory mechanism was investigated and was shown to be dependant of bacteriocin production. The objective was to isolate LAB with antibacterial activity from raib and to select strains that could be used for the determination of probiotic properties. Results showed that 6 LAB cultures retained activity in the supernatants after neutralization and catalase treatment. Streptococcus thermophilus T2 strain showed the wide inhibitory spectrum against the Gram positive bacteria. Growth and bacteriocin production profiles showed that the maximal bacteriocin production by S. thermophilus T2 cells was measured by the end of the late-log phase (90 AU ml⁻¹) with a bacteriocin production rate of 9.3 (AU ml^-1 h^-1). In addition, our findings showed that the bacteriocin, produced by S. thermophilus T2, was stable over a wide pH range (4 - 8), indicating that such bacteriocin may be useful in acidic as well as non acidic food. This preliminarily work shows the potential application of autochthonous lactic acid bacteria to improve safety of traditional fermented food. Around 40% of these strains, mainly isolated from Algerian fermented milks in MRS agar, were pre-selected for testing as potential probiotics by their ability to grow adequately at low pH values. In vivo study indicates that number of Sc T2 and Lb. B2 remains important as long as rabbits consume some fermented products. Antibacterial activity of Lactobacillus and Streptococcus against indicator bacteria is a good probiotic property. Transfer of these antimicrobial activities to in vivo conditions is beneficial for the maintenance of the intestinal microflora.

Key words: Bacteriocin, lactic acid bacteria, Streptococcus thermophilus.Lactobacillus bulgaricu, probiotic.

Abbreviation

 LAB, Lactic acid bacteria; CFU, colony forming HPLC, high performance liquid chromatography