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Characterisation of antimicrobial producing staphylococci from the human skin microbiota
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Date
2019-12
Authors
O'Sullivan, Julie N.
Journal Title
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Publisher
University College Cork
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Abstract
This thesis outlines a study of the identification and characterisation of novel antimicrobial peptides, primarily bacteriocins produced by the human skin microbiota. Bacteriocins are small ribosomally synthesised heat stable peptides produced by bacteria to aid their establishment in an environment and/or kill off competitors. This study successfully demonstrates the antimicrobial capability of human skin and shows how a variety of methods can be used for the identification and production of novel antimicrobials.
Chapter 1, a literature review, gives an overview of current and potential alternative biological tools that can be utilised in place of antibiotics in the treatment of skin infections. Such alternatives include antimicrobial peptides - bacteriocins, bacteriophage, probiotics and prebiotics which could be used to manipulate the skin microbiota. This review also examines the current evidence of the gut-skin axis.
The human skin microbiome naturally harbours hundreds of diverse bacterial species which represent part of the body’s first line of defence against the external world. This commensal microbiota contributes to host health and is thought to be involved in protection of the host against a range of infections. In this respect, the production of antimicrobial compounds is likely to be one of the defence mechanisms of the host microbiota. With drug resistance increasing, alternative antimicrobial therapies such as bacteriocins are being investigated. Chapter 2 outlines a screening study of the human skin microbiota to isolate and characterise bacteriocin-producing bacteria populating the human skin surface. Traditional colony isolation and screening procedures led to the identification of thirteen genetically distinct antimicrobial-producing staphylococci, highlighting the antimicrobial potential of the human skin microbiota.
Chapter 3 outlines the characterisation of a novel nisin variant, nisin J. Nisin J is produced by an antimicrobial producing Staphylococcus capitis strain, APC 2923, isolated from a human toe webspace area as part of our screening study in Chapter 2. As a nisin variant, nisin J is a member of class 1a lantibiotics, and displays a broad range inhibitory activity
Chapter 4 describes the discovery and characterisation of a novel bacteriocin called homicin produced by three Staphylococcus hominis strains APC 3675, APC 2924 and APC 2925. Homicin was identified in two separate studies conducted by our group; a vaginal screening study and the skin screening study reported in Chapter 2. Combining both mass spectrometry and genomic screening, homicin was found to be a three component lantibiotic, consisting of an alpha and two beta peptides and displays a narrow spectrum of antimicrobial activity inhibiting Group B streptococci and Corynebacterium species.
Chapter 5 outlines a method for the heterologous expression of natural nisin variants- nisin J, H and P in Lactococcus lactis. Many nisin variants are produced by non-GRAS approved strains which are often referred to as opportunistic pathogens. With the looming antibiotic resistance crisis these broad-spectrum variants must be harnessed for future alternative antimicrobial therapies. This study involved successfully fusing the nisin A leader to each of the structural genes of nisin J, H and P and expressing these peptides in L. lactis NZ9800 under the control of the nisin A promoter, demonstrating the robustness of the nisin A biosynthetic machinery.
The aim of this thesis was to stimulate interest in skin microbiota research, which is currently about 10 years behind gut research, and demonstrate its antimicrobial potential particularly with reference to bacteriocin discovery, characterisation and application. This work presents the discovery two novel bacteriocins isolated from the skin, which have either a broad or narrow spectrum of inhibitory activity.
This study also outlines a method to express nisin variants utilising the nisin A machinery, providing a plausible direction for future developments in bacteriocin expression in non-pathogenic hosts. Overall, this thesis highlights the antimicrobial potential that can be harnessed from the skin microbiota which could be applied to both academia and industry.
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Controlled Access
Keywords
Bacteriocins , Lantibiotics , Human skin microbiota , Novel antimicrobial therapies , Antimicrobial resistance , Skin microbiome
Citation
O'Sullivan, J. N. 2019. Characterisation of antimicrobial producing staphylococci from the human skin microbiota. PhD Thesis, University College Cork.