Identification of PblB mediating galactose-specific adhesion in a successful Streptococcus pneumoniae clone

Abstract

The pneumococcal genome is variable and there are minimal data on the influence of the accessory genome on phenotype. Pneumococcal serotype 14 sequence type (ST) 46 had been the most prevalent clone causing pneumonia in children in Taiwan. A microarray was constructed using the genomic DNA of a clinical strain (NTUH-P15) of serotype 14 ST46. Using DNA hybridization, genomic variations in NTUH-P15 were compared to those of 3 control strains. Microarray analysis identified 7 genomic regions that had significant increases in hybridization signals in the NTUH-P15 strain compared to control strains. One of these regions encoded PblB, a phage-encoded virulence factor implicated (in Streptococcus mitis) in infective endocarditis. The isogenic pblB mutant decreased adherence to A549 human lung epithelial cell compared to wild-type NTUH-P15 strain (P = 0.01). Complementation with pblB restored the adherence. PblB is predicted to contain a galactose-binding domain-like region. Preincubation of NTUH-P15 with D-galactose resulted in decreases of adherence to A549 cell in a dose-dependent manner. Challenge of mice with NTUH-P15, isogenic pblB mutant and pblB complementation strains determined that PblB was required for bacterial persistence in the nasopharynx and lung. PblB, as an adhesin mediating the galactose-specific adhesion activity of pneumococci, promote pneumococcal clonal success.

The Variable Region of Pneumococcal Pathogenicity Island 1 Is Responsible for Unusually High Virulence of a Serotype 1 Isolate

“…The reduced ability of the 4496⌬⌽ mutant to adhere to live A549 cells and its reduced capacity to form a biofilm on fixed A549 monolayers are consistent with the reduced capacity of the mutant to establish infection within the lungs which was observed following intranasal challenge in mice. The impact of the ⌬⌽ mutation on adherence to Detroit 562 nasopharyngeal cells was less pronounced, which is consistent with the lesser, but still statistically significant, effect on colonization of the murine nasopharynx at 24 h. These findings are also consistent with the recently published report that phageencoded PblB plays a role in adherence to the lung epithelium in serotype 14 pneumococci (14). The fact that a difference was observed in the present study only at early time points, whereas the mutant serotype 14 strain was reduced in numbers in the lung over longer time periods, may be a function of the distinct virulence profiles.…”

“…Interestingly, in our study significantly fewer platelets were found in the circulation of mice challenged with the wild type than in those challenged with the phage-deficient strain. While differences in platelet aggregation were not observed in blood smears, the PblB-encoding phage clearly has some impact on the number of circulating platelets, perhaps through its recently reported ability to mediate attachment to platelets (14). However, while the AR1 phage appears to have some impact on the early stages of lung infection by the serotype 1 strain, the mutant and the wild type progress to fulminant infection at similar rates.…”

“…Previous work has shown that the protein encoded by other pblB genes mediates attachment to platelets (14,26). Therefore, we investigated whether the ⌬⌽ mutation would lead to any change 2 CFU in all niches; at 24 h and 36 h, this equates to 10 2 CFU in nasopharynx and lung and to 2 ϫ 10 2 CFU in the pleural lavage fluid and blood.…”

“…The prophage includes a gene with sequence similarity to the plateletbinding protein gene (pblB) and a gene encoding an endolysin, both of which were shown to be required for the virulence of Streptococcus mitis in an animal model of infective endocarditis (13). In addition, the product of pblB has been shown to promote persistence within the murine nasopharynx and lungs of the serotype 14 ST46 clone as well as increased adherence to the lung and nasopharyngeal epithelium (14). However, the role that the phage plays in more highly virulent strains, such as serotype 1 clinical isolates, is not clear.…”

Phage-Derived Protein Induces Increased Platelet Activation and Is Associated with Mortality in Patients with Invasive Pneumococcal Disease

“…In this study, we performed a genome-wide association study (GWAS) on 349 pneumococcal draft genomes of blood isolates from patients who were admitted with IPD to two Dutch hospitals. We identified a significant association between 30-day mortality and the presence of pblB , encoding a platelet binding protein that was also reported to function in adhesion (8). In a subsequent functional study, we investigated the induction of phage-derived pblB expression by fluoroquinolones in S. pneumoniae .…”