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Validation of UDPG:PP as an anti‐virulence drug target against Streptococcus pneumoniae infections using Galleria mellonella as an alternative in vivo model

Book - Dissertation

The pneumococcus Streptococcus pneumoniae is considered one of the most important human pathogens. Infection can lead to diseases such as meningitis, pneumonia and otitis media. Especially children, the elderly and immunocompromised patients are at risk for developing severe infections. While several vaccines exist, they do not cover the entire pneumococcal spectrum. Moreover, a switch towards non-vaccine serotypes has been observed. Also, pneumococci are developing resistance towards commonly used antibiotics. With both prophylactic and therapeutic treatments failing, there is a dire need for novel antimicrobials to combat these infections. Apart from the development of novel antimicrobials, improving the reaction of the host’s immune system by lowering bacterial virulence has been proposed. This dissertation focusses on the validation of a novel anti-virulence drug target against pneumococci. In order to adequately evaluate such a novel target, animal models are indispensable. However, in early research stages the costs of optimizing and implementing a novel model do not always outweigh the benefits. Therefore, a novel alternative in vivo model using Galleria mellonella larvae was chosen. These larvae were infected with several pneumococcal strains, after which parameters such as larval survival, bacterial burden, effect of antibiotic treatment and others were assessed. Also, the model’s use in studying the pneumococcal polysaccharide capsule was demonstrated. The polysaccharide capsule is considered the most important pneumococcal virulence factor, as it is involved in adherence to epithelial cells and biofilm formation in the nasopharynx and in evasion of the innate immune system. However, due to its high heterogeneity, using this capsule or its associated enzymes as drug target has been challenging. Prior to this dissertation, an enzyme present in all pneumococci regardless of capsular serotype, uridine diphosphate glucose pyrophosphorylase (UDPG:PP), was discovered to be involved in capsule production. First, the effect of a mutation in the corresponding UDPG:PP gene was assessed. The abolishment of a thick polysaccharide capsule in mutants was confirmed microscopically and mutants were more prone to phagocytosis by macrophages in vitro. Moreover, their virulence in the alternative G. mellonella infection model was significantly lowered compared to non-mutated pneumococci. Next, in silico predicted UDPG:PP inhibitors were assessed. In vivo virulence was significantly lowered and a decrease of capsule was observed. While the molecules were probably not capable of fully inhibiting the UDPG:PP enzyme, they did alter pneumococcal virulence using UDPG:PP as a target. With this knowledge, UDPG:PP inhibitors should be further studied as potential novel anti-virulence therapy.
Number of pages: 200
Publication year:2021
Keywords:Doctoral thesis
Accessibility:Closed