Abstract
Streptococcus pneumoniae is a human pathogen responsible for high morbidity and mortality worldwide. Disease is incidental and is preceded by asymptomatic nasopharyngeal colonization in the form of biofilms. Simultaneous colonization by multiple pneumococcal strains is frequent but remains poorly characterized. Previous studies, using mostly laboratory strains, showed that pneumococcal strains can reciprocally affect each other’s colonization ability. Here, we aimed at developing a strategy to investigate pneumococcal intra-species interactions occurring in biofilms. A 72h abiotic biofilm model mimicking long-term colonization was applied to study eight pneumococcal strains encompassing 6 capsular types and 7 multilocus sequence types. Strains were labeled with GFP or RFP, generating two fluorescent variants for each. Intra-species interactions were evaluated in dual-strain biofilms (1:1 ratio) using flow cytometry. Confocal microscopy was used to image representative biofilms. Twenty-eight dual-strain combinations were tested. Interactions of commensalism, competition, amensalism and neutralism were identified. The outcome of an interaction was independent of the capsular and sequence type of the strains involved. Confocal imaging of biofilms confirmed the positive, negative and neutral effects that pneumococci can exert on each other. In conclusion, we developed an experimental approach that successfully discriminates pneumococcal strains growing in mixed biofilms, which enables the identification of intra-species interactions. Several types of interactions occur among pneumococci. These observations are a starting point to study the mechanisms underlying those interactions.
Highlights
Streptococcus pneumoniae is an important bacterial pathogen associated with high morbidity and mortality worldwide (GBD, 2018)
Disease is a rare event compared with the frequency of asymptomatic nasopharyngeal colonization (Weiser et al, 2018)
Nasopharyngeal colonization is frequent in young children (Gray et al, 1980), where multiple pneumococcal strains can simultaneously colonize the same host, a phenomenon known as multiple serotype carriage or co-colonization (Turner et al, 2011; Valente et al, 2012; Wyllie et al, Pneumococcal Intra-Species Interactions In Biofilm 2014; Kamng’ona et al, 2015; Kandasamy et al, 2015; Valente et al, 2016b)
Summary
Streptococcus pneumoniae is an important bacterial pathogen associated with high morbidity and mortality worldwide (GBD, 2018). Nasopharyngeal colonization is frequent in young children (Gray et al, 1980), where multiple pneumococcal strains can simultaneously colonize the same host, a phenomenon known as multiple serotype carriage or co-colonization Several lines of evidence indicate that intra-species competition (i.e., competition between pneumococcal strains) occurs during cocolonization and has a determinant role in shaping its epidemiology and population structure. Introduction of pneumococcal conjugate vaccines worldwide indicates that, following serotype replacement, the population structure of pneumococci is reshaped due to expansion of a limited number of non-vaccine types in carriage and disease (Moore et al, 2015; Waight et al, 2015; Azarian et al, 2020). Using a mouse model of colonization, Lipsitch and co-workers showed that the presence of a resident pneumococcal strain could affect colonization by a second (challenger) strain (Lipsitch et al, 2000)
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