Evaluation of the utility of probiotics for the prevention of infections in a model of the skin

  • Tessa Prince

    Student thesis: Phd


    Probiotics have been defined as "live microorganisms which when administered in adequate amounts confer a health benefit on the host". The beneficial effects of probiotics in the gut are well described and roles including immunomodulation and colonisation resistance have been documented. Recent reports suggest that topical use of probiotic bacteria may be an effective strategy to promote skin health or inhibit disease. Therefore, in this thesis the potential of probiotics to protect skin from pathogenic bacteria was assessed using primary keratinocytes as a model system, and the skin pathogen, Staphylococcus aureus. The ability of three probiotics, L. reuteri ATCC 55730, L. rhamnosus AC413 and L. salivarius UCC118 to inhibit the growth of S. aureus was tested using well-diffusion assays and spot on the lawn assays. All three probiotics inhibited the growth of S. aureus in well-diffusion assays, though this property was dependent on growth medium. Inhibition of S. aureus growth was principally via the production of organic acids rather than bacteriocin production. Next, to determine whether probiotics could protect keratinocytes, confluent normal human epidermal keratinocytes (NHEK) were infected with S. aureus (106 CFU/ml) in the presence or absence of the probiotic (108 CFU/ml). NHEK viability was measured using trypan blue exclusion assays. L. reuteri had a significant protective effect on NHEK when applied 1h prior to (P=0.0003), or simultaneously with S. aureus (P=0.002). L. reuteri did not however protect NHEK when applied 1h after S. aureus addition. There was no change in the number of viable S. aureus in cell culture assays. To determine whether the protective effect was due to the inhibition of adhesion, NHEK were either pre-exposed to the probiotic for 1h, simultaneously exposed to the probiotic and S. aureus for 1h, or exposed to the probiotic 30 minutes after S. aureus addition for 1h. Pre-exposure of NHEK to L. reuteri (exclusion) and simultaneous exposure to L. reuteri and S. aureus (competition) resulted in significantly less staphylococci adhering to NHEK (P=0.03 and P=0.008 respectively). However when L. reuteri was added after S. aureus (displacement), the number of adherent staphylococci was not reduced. The necessity of S. aureus adherence for the inactivation of NHEK was demonstrated using a alpha5β1 integrin blocking antibody. Finally, to compare the innate response of NHEK to probiotics with S. capitis and S. aureus, TLR-2, antimicrobial peptide (AMP) expression and IL-8 production were measured. TLR-2 protein (but not mRNA) expression was reduced in the presence of S. aureus (P=0.018). NHEK pre-exposed to S. capitis prior to S. aureus infection however, exhibited elevated TLR-2 protein and mRNA expression (P
    Date of Award1 Aug 2013
    Original languageEnglish
    Awarding Institution
    • The University of Manchester
    SupervisorCatherine O'Neill (Supervisor) & Andrew Mcbain (Supervisor)


    • antimicrobial peptides
    • toll like receptors
    • probiotics
    • skin
    • S. aureus
    • adhesion
    • L. reuteri
    • keratinocytes

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