Biomedical applications for bacteriocins in infection and oncology

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Ellis, Jenna-Claire
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University College Cork
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Lantibiotics are a subclass of a group of bacterially produced antimicrobial peptides called bacteriocins. They are characterized by post-translation modifications resulting in the presence of unusual amino acid residues such as dehydroalanine (Dha), dehydrobutyrine (Dhb) and lanthionine/ methyllanthionine. Interest in using bacteriocins as alternative therapeutics in multiple settings has grown in recent years. Nisin in particular has been the subject of many studies due to it being well characterised, approved by the FDA, widely used as a food preservative (EU number E234) and having GRAS (generally regarded as safe) status. Nisin has bioengineered to generate multiple variants with advantageous properties, including enhanced antimicrobial activity. Nisin is also capable of inducing its own production (auto-induction) through the LisRK sensor kinase system. In Chapter 2 we examine the self-induction properties of a previously created nisin variant “nisinAAA” by substituting positions K12 and H31 independently, revealing that ten variants retained the ability to induce the PnisA promotor (K12K/H31H, K12V, K12Q, K12W, K12T, K12A, K12C, H31N, H31K and H31R). Amino acid substitutions at positions K12 and H31 were also made simultaneously generating the variant K12V-AAA-H31V, a variant previously shown to be trypsin and chymotrypsin resistant, but which lost its capacity for self-induction. Our results confirm that amino acid substitutions R, N and K at H31 are the only substitutions capable of maintaining autoinduction. Given that all three are cut sites for trypsin or chymotrypsin we conclude that any substitution at position H31 of the nisin-AAA variant will lead to either loss of auto-induction or a peptide which is sensitive to digestion by chymotrypsin. The number of clinically significant bacteria becoming antibiotic resistant is increasing, along with concerns of pandrug-resistance (resistance to all current drugs), emphasizing the need to introduce new therapeutics into the clinic. In Chapter 3, following an initial screening involving nisin, lacticin 3147 and several other bacteriocins, it was observed that bacteriocins could enhance the antimicrobial activity of classical antibiotics against selected clinically significant bacteria. Levels of antibiotics often associated with adverse effects and antibiotic resistance could be reduced in the presence of either lacticin 317 of nisin Z. Enhanced antimicrobial activity was seen between lacticin 3147 and penicillin G as well as vancomycin. In addition, methicillin (which is no longer used very much in clinical settings) showed partial synergistic activity in combination with nisin Z, suggesting the possibility of reviving old therapeutics with the aid of new antimicrobials. Given that the anti-cancer effects of bacteriocins have been largely unexplored, in Chapter 4 we investigate the potential use of nisn Z as an alternative treatment for colorectal and oesophageal cancers, which have with high incidence and poor prognosis. It was observed by morphological examination that nisin Z elicited apoptotic cell death in 4 colorectal cancer cell lines and potentially autophagy mediated cell death in 2 oesophageal cancer cell lines. Confocal microscopy analysis along with flow cytometry profiles further supported autophagic cell death in oesophageal cell lines, whereas apoptotic cell death was supported in colorectal cell lines by flow cytometry. Upon further analysis it was observed that one colorectal cancer cell line, HCT116, initiated apoptotic cell death through the intrinsic pathway, as inferred by the upregulation of the protein caspase-9. As a consequence of the studies presented in this thesis, it is possible that strategies will emerge to facilitate the use of bacteriocins such as nisin Z and lacticin 3147 in clinical settings for the treatment of multiple conditions.
Oncology , Bacteriocins , Nisin , Biomedical applications of nisin , Bioengineering of nisin , Bacteriocins as anti-cancer agents , Bacteriocins and skin pathogens , Lacticin 3147 , Bacteriocins and antibiotics
Ellis, J-C. 2018. Biomedical applications for bacteriocins in infection and oncology. PhD Thesis, University College Cork.
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