Microbial warfare: identification of microbial weapons in Streptococcus spp. colonizing the nasopharynx

• Autor(a) principal: Martinho, Mariana Agostinho Marques
• Data de Publicação: 2018
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/37049
• topic: Streptococcus; commensals; inhibition; bacteriocins; probiotics; Domínio/Área Científica::Engenharia e Tecnologia::Outras Engenharias e Tecnologias

The microbiota of the nasopharynx is a niche inhabited by several microorganisms including bacteria that are strict commensals and others that are pathobionts. Streptococcus pneumoniae is one of the latter. It is a major cause of morbidity and mortality worldwide being responsible for about 0.7 million deaths per year among children with less than 5 years of age. With the rising numbers of antibiotic-resistant bacteria, infections are increasingly difficult to treat and there is a need for new antimicrobial therapies. Currently 20-30% of pneumococcal disease worldwide are caused by multidrug resistant strains. Commensal streptococci of the respiratory tract could be used as a promising alternative to antibiotics as some produce antimicrobial molecules, called bacteriocins with narrow-spectrum activity against other bacteria. The aim of this thesis was to identify commensal streptococci strains that would be able to inhibit S. pneumoniae strains, and to identify the bacteriocin loci in their genome potentially responsible for the observed phenotype. Inhibitory assays to assess inhibitory profiles of streptococcal strains against a collection of pneumococci were done. Whole-genome sequencing (WGS) was done in selected streptococci strains and the data was analyzed for the presence of putative bacteriocin loci. Three Streptococcus mitis strains had high inhibitory activity against S. pneumoniae strains while being immune to them. These strains had low inhibitory activity against other commensal streptococci strains. WGS analysis identified putative bacteriocin loci in these strains. Two blp and three lantibiotic putative loci were found in S. mitis strains. The results obtained in this thesis show that there are commensal streptococci strains capable of inhibiting S. pneumoniae which could be of interest for further studies aiming to develop alternatives to antibiotics.