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Harnessing antimicrobial bacteriocin production of probiotic bacteria

Joyce, Tamsin Susan Charley 2020. Harnessing antimicrobial bacteriocin production of probiotic bacteria. MPhil Thesis, Cardiff University.
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Bacteriocins are ribosomally-synthesised antimicrobial peptides, and their production by probiotic bacteria is extremely common, particularly in Lactobacillus species. This can be advantageous, giving them a competitive advantage over other microorganisms. However, in the production of probiotics,they can affect recovery of all the microorganisms present, thereby, causing an underestimation of the total viable bacterial numbers in commercial products. To ensure regulatory compliance, a significant additional microbial inoculum is added to these products to compensate for poor recovery. This is a huge commercial economic burden and prompted exploration into which strains were responsible for the observed antibacterial effects. In this study, neutralised cellfree supernatants (CFSs) of lactic acid bacteria (LAB), L. salivarius CUL61 and L. paracasei CUL08 were evaluated for potential antimicrobial inhibition against themselves, other probiotic bacteria (L. acidophilus CUL60 and CUL21, Bifidobacterium bifidum CUL20 and Bifidobacterium animalis subsp. Lactis CUL34) and against two commercial probiotic consortia (Lab4 and Lab4b). CFSs were obtained from bacterial cultures grown in MRS broth under planktonic or biofilm growth conditions and harvested at different time-points (5, 24, 48, and 72 h) to determine the optimum growth conditions for bacteriocin production. Harvested CFSs were neutralised, filter-sterilised and concentrated (lyophilised) prior to use. Antibacterial susceptibility testing of CFSs (singlestrength or 50% concentrated) was performed using growth curves, welldiffusion, microbroth dilution and biofilm formation assays. L. salivarius CUL61 and L. paracasei CUL08 showed antimicrobial activity against themselves, other probiotic bacteria, and commercial probiotic consortia. Antimicrobial activity was highest during late exponential/early stationary phase (24, 48, 72 h), and greater in liquid-medium (growth curve, microbroth dilution and biofilm formation assays) than in solid media (well-diffusion assays). Unsurprisingly, the genomes of both bacteria were found to harbour genes encoding bacteriocins. This study confirms long-observed findings during commercial production. A greater understanding of putative bacteriocin synthesised by LAB could help to improve and optimise production of mixed-population probiotics.

Item Type: Thesis (MPhil)
Date Type: Completion
Status: Unpublished
Schools: Dentistry
Subjects: Q Science > Q Science (General)
Uncontrolled Keywords: probiotics; lactic acid bacteria; Lactobaccillus; bacteriocins; antimicrobial
Date of First Compliant Deposit: 23 November 2020
Last Modified: 23 Nov 2020 09:33

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