Antimicrobial activity of probiotic bacteria

Probiotic strains were isolated from different cheeses (turkey and domiatii and cottage and kariesh cheese) and fermented products (yoghurt, raib, zeer milk and kishk). The isolates  were screened for   rate of growth increase in MSR broth at pH 3, pH4, acid production after 48 hours and degree of bile salt (0.3%) tolerance, strength of adhesion and clotting time (3 to 48 hrs) of  skim milk. The good fourteen isolates identified as two  Lactobacillus spp (S4b1 and S2a3), eleven Bifidobacterium spp. (RC1 b8, RC2 b1, SC1a4, RC4b2, FC1b1, RC2b4, RC4a3, LZ1a3 and LZa7) and one Streptoococcus spp. (RC2b3), were used against several human (Staphyllococcus aureus. and Eschericia coli) and plant (Rhizoctonia solani and Fusarium oxysporum) pathogens by examining their in vitro antimicrobial properties.
Antibacterial activity of the good fourteen selected probiotic isolates in this test exhibited varying degrees of inhibitory activity against human pathogenic Staphyllococcus aureus. The isolates LZb8, S4b1 and RC2b3 exhibited the superior antibacterial activity with inhibition zones (I.Z.) ranged 8.3 - 8.4 mm followed by the isolates Kb2, LZa7 and Y2a5. The least activity was recorded for the isolates SCa4 and RC4b2 (I.Z.) ranged 2.3-2.5 mm. The antibacterial activity of the same probiotic isolates against human pathogenic Eschericia coli was almost similar to that obtained against S. aureus, and followed the same pattern. The isolates LZb8, S4b1 and RC2b3 possessed the highest activity, while the isolates SCa4 and RC4b2 were highly significantly the least active. It seems that the inhibitory activity of the isolates against E. coli was slightly less as compared to that obtained against S. aureus.
The antifungal activity of the same14 probiotic isolates was tested against the plant pathogenic Rhizoctonia solani and Fusarium oxysporum. All probiotic isolates were highly significantly active on both fungi as compared to the control, showing % growth inhibition (%GI) ranges of 26.7-52.3 %, and 17.1 -51.2 % against the first and the latter fungi, respectively . The most active isolates against R. solani were RC4b2 (52.3 % GI), followed by both RC4b3 and RC1b8 (47.6 % GI). Also, the most active isolate against F. oxysporum was Y2a5 (51.2 GI).