Document Type

Theses, Masters


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Publication Details

A Thesis Presented for the Award of Masters by Research, Technological University Dublin, 2021.


Bifidobacteria are a species of GRAS organism present in the human gut flora which are claimed to confer various health benefits on the host. The antimicrobial activity of Bifidobacterium longum ITT 13, isolated from the neonatal gut, was evaluated in relation to both the contribution of organic acids produced by the strain and potential bacteriocin production. Bacteriocins are antimicrobial peptides produced by bacteria. This study focuses on the characterisation of the antimicrobial activity produced by B. longum ITT 13.

Heat-inactivated fermentate produced by ITT 13 has shown antimicrobial activity against a variety of pathogenic and food spoilage associated bacterial and fungal strains. Physiochemical characterization of the antimicrobial activity has shown that pH stability testing has indicated activity at pH 5 and below, with activity not detectable above pH 6. Temperature stability testing has indicated stability of the antimicrobial activity at a temperature range of -20oC to 100oC, with maximum activity (133-213 Activity Units/ml) retained for 48 hours at 4oC and room temperature (20oC to 24oC). Antimicrobial activity was found to be partially caused by organic acid production, as the heterofermentative Bifidobacteria produce several acids during growth. HPLC analysis determined between 6 mg/ml and 10 mg/ml lactic, acetic and succinic acid produced by B. longum ITT 13 when grown in De Man, Rogosa and Sharpe broth with and without pH control. Protease digestion by Actinase E resulted in a reduced minimum inhibitory concentration of antimicrobial activity and 80% ammonium sulphate precipitation of the fermentate resulted in the detection of antimicrobial activity in the resuspended precipitate, indicating the presence of antimicrobial activity associated with a low molecular weight proteinaceous molecule. Concentration studies on the antimicrobial activity of the fermentate involved membrane filtration via tangential flow filtration. Use of a 10KDa and 3 kDa filter showed similar antimicrobial activity present in both the retentate and permeate, together with probable adsorption of the proteinaceous molecule to the membrane, as it is present in low concentrations.

Experimental results indicate that the antimicrobial activity associate with B. longum ITT 13 is due to a combination of the production of acids together with a proteinaceous component. Further studies, using higher starting concentrations of fermentate, could be used to concentrate and isolate the bacteriocin component of the detected antimicrobial activity.


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