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Characterization of commensal strains with bacteriocinmediated inhibition against Streptococcus pneumoniae
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Resumo(s)
The microbiota of the upper respiratory tract (URT) plays an important role in protecting the host
against respiratory pathogens. Most of the microbial communities in the URT are commensal bacteria.
However, some of the colonizers are opportunistic pathogens such as Streptococcus pneumoniae. S.
pneumoniae is a Gram-positive bacterium responsible for causing infections such as otitis media,
sinusitis, meningitis, bacteremia and pneumonia. Such infections remain common among children,
elders and immunocompromised patients despite the introduction of vaccines. Furthermore, the
emergence of antibiotic resistance has narrowed the treatment options. Previously at the Molecular
Microbiology of Human Pathogens Laboratory, seven strains were identified as commensal streptococci
- Streptococcus oralis and Streptococcus mitis - which inhibited most strains of a diverse pneumococcal
collection. The genomic analysis of these commensal strains identified multiple putative bacteriocin
loci. In this work, the inhibitory potential of three bacteriocin loci (B2 from a S. oralis strain and B6 and
C3 from a S. mitis strain) against the pneumococci was evaluated. Deletion mutants for each locus were
constructed and cell-free supernatants were obtained and tested for inhibitory potential. A partial loss of
inhibition was observed when the supernatants of the B2 and B6 loci deletion mutants were tested
against pneumococci in well-diffusion assays and during planktonic growth. Bacterial cytological
profiling was performed to obtain insights on the mechanism of action of the bacteriocins in the loci
under study. Fluorescence microscopy imaging suggested an increased permeability in cells treated with
the supernatant of the S. mitis wild-type strain which was not observed in cells treated with the
supernatant of the corresponding B6 deletion mutant. In conclusion, in the conditions tested the
bacteriocins from the B2 and B6 loci have a small effect on the inhibition of S. pneumoniae. The B6
locus possibly targets the pneumococcal cell membrane leading to its disruption.
Descrição
Tese de mestrado, Microbiologia Aplicada, 2022, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Streptococcus oralis Streptococcus mitis Streptococcus pneumoniae bacteriocinas bacterial cytological profiling Teses de mestrado - 2023