Bioengineering strategies to improve functional qualities of nisin

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dc.contributor.advisor Hill, Colin en
dc.contributor.advisor Ross, R. Paul en
dc.contributor.advisor Cotter, Paul D. en Campion, Alicia M. 2016-05-31T10:27:00Z 2016-05-31T10:27:00Z 2016 2016
dc.identifier.citation Campion, A. M. 2016. Bioengineering strategies to improve functional qualities of nisin. PhD Thesis, University College Cork. en
dc.description.abstract The abuse of antibiotics and the emergence of multi-drug resistant bacterial strains have created the need to explore alternative methods of controlling microbial pathogens. The bacteriocin family of antimicrobial peptides has been proposed as one such alternative to classic antibiotics. Nisin A belongs to the subgroup of bacteriocins called the lantibiotics, which contain several unusual amino acids as a consequence of enzyme-mediated post-translational modifications. As nisin is produced by generally regarded as safe (GRAS) microorganisms, it could potentially be applied in a clinical setting. However, as lantibiotics are naturally produced in such small quantities, this can hinder their industrial potential. In order to overcome this, several approaches can be utilised. For example, given the gene encoded nature of lantibiotics, genetic engineering approaches can be implemented in order to yield variants with enhanced properties. Here, the use of mutagenesis-based strategies was employed to obtain a derivative of nisin with enhanced bioactivity in vitro. Investigations with purified peptide highlighted the enhanced specific activity of this variant, nisin M21V, against food-borne Listeria monocytogenes strains. Furthermore, this specific enhanced bioactivity was evident in a mouse model of listeriosis. Reductions in bioluminescence and microbial counts in organs from infected mice were observed following treatment with nisin M21V compared to that of wild-type nisin A. Peptide bioengineering approaches were also implemented to obtain additional novel derivatives of nisin. The generation of “S5X” and “S33X” banks (representing a change of natural serines at positions 5 and 33 to all possible alternative residues) by a combination of site-saturation and site-directed mutagenesis led to the identification of several derivatives exhibiting improved stability. This allowed the rational design of variants with enhanced stability compared to that of wild type nisin. Another means of tackling issues associated with lantibiotic yield is to combine lantibiotics with other antimicrobials. This could circumvent the need for enhanced production while also reducing concentrations of the peptide antimicrobials. We observed that combinations of nisin variants and low levels of plant essential oils (thymol, carvacrol, trans-cinnamaldehyde) significantly controlled Gram negative foodborne pathogens in in vitro assays compared to nisin A-essential oil combinations. This enhanced control was also evident in model food systems. Nisin variants used in conjunction with carvacrol significantly reduced numbers of E. coli O157:H7 in apple juice while a commercial nisin preparation used in combination with citric acid significantly controlled C. sakazakii in infant milk formula. It is noteworthy that while nisin is generally associated with Gram positive targets, upon combination with plant essential oils the spectrum of inhibition was broadened to Gram negative targets. en
dc.description.sponsorship Higher Education Authority (Programme for Research in Third-Level Institutions (PRTLI) Cycle 5) en
dc.format.mimetype application/pdf en
dc.language.iso en en
dc.publisher University College Cork en
dc.rights © 2016, Alicia M. Campion. en
dc.rights.uri en
dc.subject Lantibiotic en
dc.subject Bioengineering en
dc.subject Nisin en
dc.title Bioengineering strategies to improve functional qualities of nisin en
dc.type Doctoral thesis en
dc.type.qualificationlevel Doctoral Degree (Structured) en
dc.type.qualificationname PhD (Science) en
dc.internal.availability Full text not available en The full text of this thesis is unavailable due to a restriction requested by the author. en 10000-01-01
dc.description.version Accepted Version
dc.contributor.funder Higher Education Authority en
dc.description.status Not peer reviewed en Microbiology en
dc.check.type No Embargo Required
dc.check.reason No embargo required en
dc.check.opt-out Yes en
dc.thesis.opt-out true
dc.check.embargoformat Not applicable en
dc.internal.conferring Summer 2016 en

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© 2016, Alicia M. Campion. Except where otherwise noted, this item's license is described as © 2016, Alicia M. Campion.
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