Streptococcus pneumoniae: virulence factors, pathogenesis, and vaccines.

SummaryProteic toxin-antitoxin (TA) loci were first identified in bacterial plasmids, and they were regarded as involved in stable plasmid maintenance by a socalled 'addiction' mechanism. Later, chromosomally encoded TA loci were identified and their function ascribed to survival mechanisms when bacteria were subjected to stress. In the search for chromosomally encoded TA loci in Gram-positive bacteria, we identified various in the pathogen Streptococcus pneumoniae . Two of these cassettes, sharing homology with the Escherichia coli relBE locus were cloned and tested for their activity. The relBE 2 Spn locus resulted to be a bona fide TA locus. The toxin exhibited high toxicity towards E. coli and S. pneumoniae , although in the latter, the chromosomal copy of the antitoxin relB 2 Spn gene had to be inactivated to detect full toxicity. Cell growth arrest caused by expression of the relE 2 Spn toxin gene could be reverted by expression of the cognate antitoxin, relB 2 Spn , although prolonged exposition to the toxin led to cell death. The pneumococcal relBE 2 Spn locus is the first instance of a chromosomally encoded TA system from Grampositive bacteria characterized in its own host. We have developed a bioluminescence resonance energy transfer (BRET) assay to detect the interactions between the RelB2 Spn antitoxin and the RelE2 Spn toxin in vivo . This technique has shown to be amenable to a high-throughput screening (HTS), opening new avenues in the search of molecules with potential antibacterial activity able to inhibit TA interactions.

Section: Introductionmentioning

confidence: 99%

The chromosomal relBE2 toxin–antitoxin locus of Streptococcus pneumoniae: characterization and use of a bioluminescence resonance energy transfer assay to detect toxin–antitoxin interaction

Nieto

Pellicer²,

Balsa³

et al. 2006

“…The S. pneumoniae polysaccharide capsule, of which there are at least 90 serotypes, is antiphagocytic and a major virulence determinant (AlonsoDeVelasco et al, 1995). However, the current pneumococcal polysaccharide vaccine comprising 23 capsular serotypes is of limited clinical efficacy because of poor immunogenicity in the high-risk groups, especially infants (Paton, 1998).…”

Section: Introductionmentioning

confidence: 99%

The pavA gene of Streptococcus pneumoniae encodes a fibronectin‐binding protein that is essential for virulence

Holmes

McNab

Millsap

et al. 2001

203

223

Streptococcus pneumoniae colonizes the nasopharynx in up to 40% of healthy subjects, and is a leading cause of middle ear infections (otitis media), meningitis and pneumonia. Pneumococci adhere to glycosidic receptors on epithelial cells and to immobilized fibronectin, but the bacterial adhesins mediating these reactions are largely uncharacterized. In this report we describe a novel pneumococcal protein PavA, which binds fibronectin and is associated with pneumococcal adhesion and virulence. The pavA gene, present in 64 independent isolates of S. pneumoniae tested, encodes a 551 amino acid residue polypeptide with 67% identical amino acid sequence to Fbp54 protein in Streptococcus pyogenes. PavA localized to the pneumococcal cell outer surface, as demonstrated by immunoelectron microscopy, despite lack of conventional secretory or cell‐surface anchorage signals within the primary sequence. Full‐length recombinant PavA polypeptide bound to immobilized human fibronectin in preference to fluid‐phase fibronectin, in a heparin‐sensitive interaction, and blocked binding of wild‐type pneumococcal cells to fibronectin. However, a C‐terminally truncated PavA′ polypeptide (362 aa residues) failed to bind fibronectin or block pneumococcal cell adhesion. Expression of pavA in Enterococcus faecalis JH2–2 conferred > sixfold increased cell adhesion levels to fibronectin over control JH2–2 cells. Isogenic mutants of S. pneumoniae, either abrogated in PavA expression or producing a 42 kDa C‐terminally truncated protein, showed up to 50% reduced binding to immobilized fibronectin. Inactivation of pavA had no effects on growth rate, cell morphology, cell‐surface physico‐chemical properties, production of pneumolysin, autolysin, or surface proteins PspA and PsaA. Isogenic pavA mutants of encapsulated S. pneumoniae D39 were approximately 104‐fold attenuated in virulence in the mouse sepsis model. These results provide evidence that PavA fibronectin‐binding protein plays a direct role in the pathogenesis of pneumococcal infections.

“…Streptococcus pneumoniae is an important human pathogen causing community-acquired pneumonia and other diseases, yet its virulence mechanisms are not fully understood (AlonsoDeVelasco et al, 1995). A better understanding of which bacterial gene products are involved in infection would be valuable for the development of new anti-infective drugs.…”

Section: Introductionmentioning

confidence: 99%

Differential fluorescence induction reveals Streptococcus pneumoniae loci regulated by competence stimulatory peptide

Bartilson

Marra

Christine

et al. 2001

SummaryDifferential fluorescence induction (DFI) in Streptococcus pneumoniae was used as a method for the discovery of genes activated in specific growth environments. Competence stimulatory peptide (CSP) was used as the model inducing system to identify differentially expressed genes. To identify CSP-induced promoters, a plasmid library was constructed by inserting random pieces of S. pneumoniae chromosomal DNA upstream of the promoterless gfpmut2 gene in an Escherichia coli/S. pneumoniae shuttle vector. S. pneumoniae carrying the library were induced with CSP and enriched for green fluorescent protein (GFP)-expressing bacteria using fluorescenceactivated cell sorting. A total of 886 fluorescent clones was screened, and 12 differentially activated promoter elements were identified. Sequence analysis of these clones revealed that three were associated with novel competence loci, one of which we show is essential for DNA uptake, and six are known CSP-inducible promoters. We also explored whether competence proteins have a role in virulence and found that mutations in three CSP-inducible genes resulted in attenuated virulence phenotypes in either of two murine infection models. These results demonstrate the utility of DFI as a method for identifying differentially expressed genes in S. pneumoniae and the potential utility of applying DFI to other Gram-positive bacteria.