title: Biofilm formation avoids complement immunity and phagocytosis of Streptococcus pneumoniae.
abstract: Streptococcus pneumoniae is a frequent member of the microbiota of the human nasopharynx. Colonization of the nasopharyngeal tract is a first and necessary step in the infectious process and often involves the formation of sessile microbial communities by this human pathogen. The ability to grow and persist as biofilms is an advantage for many microorganisms, because biofilm-grown bacteria show reduced susceptibility to antimicrobial agents and hinder recognition by the immune system. The extent of host protection against biofilm-related pneumococcal disease has not been determined yet. Using pneumococcal strains growing as planktonic cultures or as biofilms, we have investigated the recognition of S. pneumoniae by the complement system and its interactions with human neutrophils. Deposition of C3b, the key complement component, was impaired on S. pneumoniae biofilms. In addition, binding of C-reactive protein and the complement component C1q to the pneumococcal surface was reduced in biofilm bacteria, demonstrating that pneumococcal biofilms avoid the activation of the classical complement pathway. In addition, recruitment of factor H, the downregulator of the alternative pathway, was enhanced by S. pneumoniae growing as biofilms. Our results also show that biofilm formation diverts the alternative complement pathway activation by a PspC-mediated mechanism. Furthermore, phagocytosis of pneumococcal biofilms was also impaired. The present study confirms that biofilm formation in S. pneumoniae is an efficient means of evading both the classical and the PspC-dependent alternative complement pathways the host immune system.
authors: Department of Molecular Microbiology and Infection Biology, Centro de Investigaciones Biológicas, Madrid, Spain.
authors: Mirian
authors: M
authors: Domenech
authors: Elisa
authors: E
authors: Ramos-Sevillano
authors: Ernesto
authors: E
authors: García
authors: Miriam
authors: M
authors: Moscoso
authors: Jose
authors: J
authors: Yuste
mesh_terms: D000328:Adult; D001426:Bacterial Proteins / Q000276:immunology; D018441:Biofilms; D003179:Complement C3b / Q000276:immunology; D050716:Complement C4b-Binding Protein / Q000276:immunology; D003170:Complement Pathway, Alternative; D003171:Complement Pathway, Classical; D054884:Host-Pathogen Interactions; D006801:Humans; D057131:Immune Evasion; D008297:Male; D018613:Microscopy, Confocal; D009504:Neutrophils / Q000276:immunology / Q000382:microbiology; D010587:Phagocytosis; D011008:Pneumococcal Infections / Q000276:immunology* / Q000382:microbiology; D013296:Streptococcus pneumoniae / Q000276:immunology* / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; C055609:C4BPA protein, human; D050716:Complement C4b-Binding Protein; C110344:SpsA protein, Streptococcus pneumoniae; D003179:Complement C3b
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