AbstractsBiology & Animal Science

The World Health Organization states that adults worldwide have a prevalence of almost 100% for dental caries and 15-20% for severe periodontal diseases. Astonishingly, the prevalence of oral candidiasis is high in HIV patients which stand at 40-50%. The main therapeutics targets for these diseases are pathogen inhibition, limiting oral inflammation and restoring lost oral tissue. Current treatments have limitations, as suggested by the high disease prevalence rates. More importantly, the chronicity of oral diseases requires a natural and safe long-term therapy. Probiotic bacteria, with recent works investigating the oral microbiome, have gained great interest for the development of biotherapeutics. The goals of this thesis includes screening Lactobacillus strains for the inhibition of Streptococcus mutans, and Candida albicans, dental caries and oral candidiasis causing microorganism, respectively. Following the selection of probiotic strains, probiotic characteristics such as probiotic bacteriocin activity, salivary pH modulation, probiotic nutrient (sucrose) competition, probiotic co-aggregation with S. mutans, bacterial attachment to oral epithelial keratinocytes, bacterial nitric oxide production and bacterial antioxidant activity were investigated. Lactobacillus reuteri and Lactobacillus fermentum strains demonstrated oral health promoting characteristics when compared to S. mutans. This was followed by investigations into probiotic hydrogen peroxide production, as hydrogen peroxide has important implications in oral health, including its antimicrobial and whitening properties. Indeed, it was demonstrated that the L. reuteri mechanism of S. mutans inhibition was directly correlated to peroxide production, as investigated using catalase inactivation of hydrogen peroxide. L. reuteri NCIMB 701359, the probiotic with the highest level of hydrogen peroxide production, demonstrated significant reduction in S. mutans biofilm formation, as investigated in a developed model of biofilm under simulated oral conditions. Chronic inflammation and loss of oral tissue are characteristics of periodontal diseases. L. fermentum NCIMB 5221 treatment demonstrated significant reductions in pro-inflammatory cytokines secreted by inflamed osteoblast-like cells. Of potentially even greater interest for periodontitis, the probiotic L. fermentum NCIMB 5221 was also shown to promote the growth of osteaoblast-like cells. In vivo studies shows that L. fermentum NCIMB 5221 modulated serum calcium levels demonstrating their potential role for bone remodeling. Also, a novel oral thin film (OTF) was developed using carboxymethyl cellulose (CMC), to improve the delivery and residence of probiotic bacterial cells into the oral cavity. Following film characterisation and optimization, L. fermentum NCIMB 5221 was incorporated in the films. The probiotic-CMC-OTFs when stored long-term at room temperature, did not change bacterial cell viability and anti-oxidant activity for 150 days. This novel work demonstrates the potential of probiotic bacterial…