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Probiotic interaction with common skin pathogens: Understanding the impact of probiotics on pathogen function and metabolism within the host

Al-Dulaimy, Duaa 2021. Probiotic interaction with common skin pathogens: Understanding the impact of probiotics on pathogen function and metabolism within the host. PhD Thesis, Cardiff University.
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Introduction: Skin and soft tissue infections (SSTIs) are considered a major public health problem in many countries. Pathogenic bacteria have evolved complex mechanisms for infection and colonization of numerous host cells. Despite the presence of various antibiotics for the treatment of infectious diseases, their random, inappropriate and excessive use has resulted in increasing incidence of several side effects and the development of antimicrobial resistance. Consequently, there is an urgent need to develop new and safe treatments for infections, especially those of the skin. Different new therapeutic approaches are currently being increased such as bacteriotherapy using probiotics. Dairy and non-dairy fermented foods have been used in traditional diets worldwide and are still to be broadly consumed, since they are considered as rich sources of probiotics, especially lactic acid bacteria. From commencement to cure, the progress and severity of infectious diseases are continuously affected by the interaction between the pathogen and the host. Therefore, investigations performed both in vitro and in vivo are important when determining the health- enhancing properties of probiotics. The greater wax moth larvae Galleria mellonella is a well-accepted model of infection by scientists, as an in vivo model for host-pathogen interactions due to several advantages, such as its low cost and no required ethical rights to be used in the experiments in vivo. Aim: This project aimed to investigate the antagonistic activity of Lactobacillus type strains and food isolates against the major causative agents of skin infections in vitro. It also aimed to explore the therapeutic potency of food-derived Lactobacillus species against skin pathogens, using both the injection method inside the Galleria mellonella larvae model, and the topical application on the larvae as a novel technique for infections and treatment which can assist in decreasing the occurrence of skin infections. Results: A total of twenty Lactobacillus species, including ten type strains obtained from different culture collections and ten food isolates derived from fermented yogurt and olives, all revealed significant inhibitory activity against the three skin pathogens used in this study; Staphylococcus aureus, Streptococcus pyogenes and Streptococcus dysgalactiae subsp. equisimilis. Although the antagonistic effect was observed after the first day of incubation under both aerobic and anaerobic incubation conditions, the maximum antibacterial effect was detected following three days of anaerobic incubation. Furthermore, food-isolated Lactobacillus presented a higher inhibitory effectiveness than the type strains against the pathogens xx particularly under the anaerobic conditions. Characterisation of bacterial genomes by whole genome sequence (WGS) analysis showed that the sequenced genomes of food lactobacilli had a number of genes encoding for antimicrobial substances, in addition to other genes responsible for probiotic advantages. Multiple genes encoding for virulence factors were also detected in the pathogenic sequenced genomes. Diversity of the bacterial community of food samples by next generation sequencing (NGS) of 16S rRNA gene amplicons revealed that Lactobacillus delbrueckii isolated from yogurt by the culture-dependent procedure was found in low abundance as Lb. delbrueckii subsp. indicus using the culture-independent method. Despite the isolation of Lactobacillus plantarum from olives using culturing technique, no signal was observed for this species by NGS. Injection of Lb. delbrueckii and Lb. plantarum isolated from fermented foods in G. mellonella larvae presented a significant therapeutic activity of both species against pathogenic infections in a dose-dependent matter. Both the injected doses, 102 CFU/larva and 104 CFU/larva of Lb. delbrueckii washed cells, were effective in reducing S. aureus and S. pyogenes infections. Whereas the low injected dose of this species had more activity than the higher one to decrease the infection of S. dysgalactiae subsp. equisimilis in the larvae. Regarding Lb. plantarum, the doses of 103 CFU/larva and 104 CFU/larva injected in the larvae were both useful in reducing S. aureus infection, with more efficiency for the low dose. However, both doses had no therapeutic effect against S. pyogenes infection. The novel topical application technique of S. pyogenes cells on the dorsum of larvae followed by the application of Lb. plantarum washed cells and undiluted cell free supernatant (CFS) resulted in lower death rates of the treated larvae in comparison to the control group. Nevertheless, bacterial cells of Lb. plantarum revealed more activity than the CFS of the same species. Conclusions: The significant antagonistic effect in vitro and the significant therapeutic potency of food Lactobacillus species against skin pathogens, indicate that food-derived Lactobacillus isolates included in this study could act as potential candidates with promising probiotic advantages. This research delivers the basis for further investigation on the treatment of skin infections with food lactobacilli. Moreover, these food-based Lactobacillus species could be introduced as topical formulations to decrease the symptoms of skin infections or even in the context of skin infection treatments.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Biosciences
Subjects: Q Science > Q Science (General)
Date of First Compliant Deposit: 18 June 2021
Last Modified: 18 Jun 2022 01:30

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