Hyperencapsulated mucoid pneumococcal isolates from patients with cystic fibrosis have increased biofilm density and persistence in vivo

Abstract

Mucoid bacteria, predominately Pseudomonas aeruginosa, are commonly associated with decline in pulmonary function in children with cystic fibrosis (CF), and are thought to persist at least in part due to a greater propensity toward forming biofilms. We isolated a higher frequency of mucoid Streptococcus pneumoniae (Sp) expressing high levels of capsular polysaccharides from sputa from children with CF, compared to those without CF. We compared biofilm formation and maturation by mucoid and non-mucoid isolates of Sp collected from children with and without CF. Non-mucoid Sp serotype 19A and 19F isolates had significantly higher levels of biofilm initiation and adherence to CF epithelial cells than did serotype 3 isolates. However, strains expressing high levels of capsule had significantly greater biofilm maturation, as evidenced by increased density and thickness in static and continuous flow assays via confocal microscopy. Finally, using a serotype 3 Sp strain, we showed that highly encapsulated mucoid phase variants predominate during late adherence and better colonize CFTR–/– as compared to wild-type mice in respiratory infection studies. These findings indicate that overexpression of capsule can enhance the development of mature pneumococcal biofilms in vitro, and may contribute to pneumococcal colonization in CF lung disease.

The Yin and Yang of Streptococcus Lung Infections in Cystic Fibrosis: a Model for Studying Polymicrobial Interactions

“…Thus, the phenotypes of the mucoid and nonmucoid S. pneumoniae strains mirror those of mucoid and nonmucoid P. aeruginosa strains (34,35). The mucoid phenotype of the S. pneumoniae isolates was due to capsule production, and these strains switched to a nonmucoid phenotype, likely via phase variation, while growing in biofilms (32,36), which is likely their mode of growth in the context of a CF-related infection.…”

“…In another study, ϳ20% of the 212 children with CF studied were shown to have detectable Streptococcus pneumoniae when oropharyngeal swab specimens were analyzed by quantitative PCR (33). Interestingly, Dennis and colleagues showed that mucoid variants of S. pneumoniae could be isolated from the sputum of children with CF (32). Furthermore, while these mucoid strains showed reduced initial biofilm formation in vitro compared to nonmucoid strains, they eventually formed more robust biofilms and were more virulent in a mouse model of CF.…”

Clinical Relevance and Molecular Pathogenesis of the Emerging Serotypes 22F and 33F of Streptococcus pneumoniae in Spain

“…Biofilm formation is a critical aspect from the pathogenesis perspective because S. pneumoniae has been reported to form biofilms in the upper respiratory tract (Wu et al, 2017;Iverson et al, 2019;Silva and Sillankorva, 2019) and nasopharyngeal colonization is the initial step in this process and the prerequisite for developing IPD (Bogaert et al, 2004). Interestingly, active infection is also associated to pneumococcal biofilms in meningitis by binding to brain microvascular endothelial cells and in persistent respiratory infection affecting patients with cystic fibrosis or chronic obstructive pulmonary disease (COPD) (Orihuela et al, 2009;Vidal et al, 2013;Vandevelde et al, 2014;Dennis et al, 2018). In the biofilm state, pneumococcal cells express the PspC protein in a higher extent, and this protein is the bacterial ligand associated to the recruitment of factor H and therefore to the cleavage of the C3 complement system protein deposited on the bacterial surface (Domenech et al, 2013).…”

Phase variation of a signal transduction system controlsClostridioides difficilecolony morphology, motility, and virulence

“…In multiple species, the production of surface factors is subject to phase variation, leading to changes in gross colony morphology. In S. pneumoniae and Acinetobacter baumannii , phase variation of capsule polysaccharides leads to the formation of either opaque or translucent colonies that differ in a multitude of phenotypes including cell morphology, biofilm formation, antibiotic sensitivity, host colonization, and virulence (6, 9, 12, 24, 26, 27). Phase variation of colony morphology is therefore an important adaptive strategy during infection for multiple pathogens.…”