Antagonisme de Bifidobacterium sp et Lactobacillus rhamnosus vis-à-vis de quelques souches pathogènes.

Abstract

Five strains of bifidobacteria (422, 431, 434, X2 and Bb12) and one lactic acid bacterium strain (Lactobacillus rhamnosus Bbv2), were examined for their antagonistic activities against five pathogenic strains Staphylococcus aureus ATCC 49444, Shigella sonnei CECT 457, Shigella dysenteria CECT 457, Listeria innocua CECT 910 et Micrococcus luteus CECT 457). At the same time, we have tested the antagonistic activity of the bifidobacteria strains and L. rhamnosus strains, towards lactic acid bacteria indicator strains: Carnobacterium maltoaromaticum CECT 5805, Lactobacillus plantarum CECT 748, Pediococcus pentosaceus CECT 4695, Lactobacillus acidophilus CECT 4529, Lactobacillus sake 673. Two methods were used to study the antagonistic activity of these strains. The first one consist to associate the tested strains with the pathogenic ones, the lecture are made with interval times: T0, T2, T4, T6, T8, T10 and T24. The second one is based on the measure of diameter inhibition zone by three different methods: SOAT (Stab On Agar Test), ADT (Agar well Diffusion Test), SPAT (Spot On Agar Test). Micrococcus luteus, the viability decrease of about: 5.46, 0.83, 1.18, 6.57, 1.41 and 6.57 log respectively for the strains 422, 431, 434, X2 and Bb12 after 24h of associated culture. After 24h of associated culture with Shigella sonnei, we have noted a loss of viability of: 5.37, 1.53, 0.88, 6.55, 2.01 and 5.99 log respectively for the strains 422, 431, 434, X2 and Bb12.The biomass loss observed with Shigella dysenteria were de about of : 2.13, 0.83, 0.84, 5.99, 3.82 et 5.40 log respectively for the strains 422, 431, 434, X2 and Bb12 after 24h of associated culture. Concerning Listeria innocua, the viability loss recorded after 24 h of associated culture: 0.013, 0.06, 0.008, 0.073, 0.05 et 0.083 log respectively for the strains 422, 431, 434, X2 and Bb12 after 24h of associated culture. Carnobacterium maltoaromaticum note a viability loss about of: 6.55, 0.90, 0.94, 6.55, 2.89 et 7.13 log respectively for the strains 422, 431, 434, X2 and Bb12 after 24h of associated culture. The two strains Bb12 and Bbv2 were the most active with associated culture. We noted a maximal inhibition zone obtained in the case of the Bb12 strain with Shigella dysenteria using the SOAT technique witch was about of 2.86cm.The biggest inhibition zones diameter obtained for the rest of the indictor strains was observed with the Bb12 strain using the SPAT technique with the according results: 1.52 cm for Micrococcus luteus, 1.63 cm for Shigella sonnei, 1.67cm for Staphylococcus aureus and 1.75 cm for Carnobacterium maltoaromaticum. 1.75 cm for Lactobacillus sake, 1.61 cm for Lactobacillus plantarum, 1.55 cm for Pediococcus pentosaceus, 1.56 cm for Lactobacillus acidophilus. The antimicrobial peptides produced by Bbv2 and Bb12 strains, was adsorbed on the producer cells at pH 6.5, then desorbed at pH 2, witch permeate to us a partial purification. The antagonistic activities of the two partially purified solutions was examined by the ADT technique towards Carnobacterium maltoaromaticum, the measure of diameter inhibition zones gives 0.96 and 2.62cm respectively for the Bbv2 and Bb12 strains. Heat (20mn at 121°C) and pepsin (200µg/ml) treatments of the two partially purified solutions have shown that the likely antagonist substances are protein made and thermoresistant.