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International Journal of Dairy Science
Year: 2007  |  Volume: 2  |  Issue: 2  |  Page No.: 116 - 125

Study of the Inhibition Effects of Bifidobacterium Supernatants Towards Growth of Bacillus cereus and Escherichia coli

A. Cheikhyoussef, N. Pogori and H. Zhang    

Abstract: The antimicrobial effects of the supernatants obtained from four strains of bifidobacteria were tested against two types of indicator strains, Bacillus cereus and three strains of Escherichia coli. E. coli AS 1.543 was the most sensitive strain among the E. coli strains whereby B. bifidum showed the highest antimicrobial activity against indicator strains followed by B. infantis then B. longum and finally B. adolescentis. There was a significant reduction in the growth of the indicator strains, whereby all E. coli strains were inhibited more than 75% of their log CFU in monoculture, of which B. infantis reduced 95% of E. coli AS 1.543. On the other hand only more than 60% of the log CFU of B. cereus was reduced by all bifidobacterial supernatants in particular B. longum (75%). It was observed that substances or factors other than organic acids may contribute to the antimicrobial activity of the supernatants (CFS) from the bifidobacteria studied. Neutralization of the CFS from B. adolescentis and B. bifidum significantly reduced the antimicrobial activity while that from B. infantis and B. longum continued to inhibit growth of the indicator strain as observed by a clear defined zone uncharacteristic of acid production by the agar diffusion method. The inactivation of the antimicrobial activity of CFS from B. infantis and B. longum by proteolytic enzymes confirms the proteinaceous nature of the antimicrobial compound present. In addition their heat and pH stability further proves the presence of a proteinaceous antimicrobial compound which could be designated as bacteriocins or bacteriocin-like compounds.

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