Genetic Loci of Streptococcus mitis That Mediate Binding to Human Platelets

Abstract

The direct binding of bacteria to platelets is a postulated major interaction in the pathogenesis of infective endocarditis. To identify bacterial components that mediate platelet binding by Streptococcus mitis, we screened a Tn916⌬E-derived mutant library of S. mitis strain SF100 for reduced binding to human platelets in vitro. Two distinct loci were found to affect platelet binding. The first contains a gene (pblT) encoding a highly hydrophobic, 43-kDa protein with 12 potential membrane-spanning segments. This protein resembles members of the major facilitator superfamily of small-molecule transporters. The second platelet binding locus consists of an apparent polycistronic operon. This region includes genes that are highly similar to those of Lactococcus lactis phage r1t and Streptococcus thermophilus phage 01205. Two genes (pblA and pblB) encoding large surface proteins are also present. The former encodes a 107-kDa protein containing tryptophan-rich repeats, which may serve to anchor the protein within the cell wall. The latter encodes a 121-kDa protein most similar to a tail fiber protein from phage 01205. Functional mapping by insertion-duplication mutagenesis and gene complementation indicates that PblB may be a platelet adhesin and that expression of PblB may be linked to that of PblA. The combined data indicate that at least two genomic regions contribute to platelet binding by S. mitis. One encodes a probable transmembrane transporter, while the second encodes two large surface proteins resembling structural components of lysogenic phages.

Metagenomic detection of phage-encoded platelet-binding factors in the human oral cavity

“…Phage SM1 is a temperate phage previously isolated from S. mitis SF100, an endocarditis strain (24). SM1 carries two genes, pblA and pblB, which contribute to S. mitis virulence in the endocardium (24)(25)(26)(27). Although S. mitis is a ubiquitous member of the normal oral flora, the presence of phage SM1 has never previously been reported in the mouth or oropharynx (1).…”

“…pblA and pblB are integral phage tail proteins, and phage with pblA and pblB gene deletions have intact capsids but no tails (24,25). pblA and pblB also mediate the attachment of S. mitis to platelets, which has been shown in a rabbit model to contribute significantly to the virulence of S. mitis in the endocardium (25)(26)(27)39). The interaction between S. mitis cells and platelets requires phage induction for maximal release of intracellular pblA and pblB, but the soluble proteins can bind to choline residues on the surface of host or nonhost cells (27,39).…”

Dental Caries: A Microbiological Approach

“…In addition, environmental conditions such as pH, temperature, oxygen availability, organic metabolites etc. may be involved in Streptococcus mitis colonization (Table 2) [107,108].…”

Molecular typing of colonizing Streptococcus agalactiae strains by enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) in a Chennai based hospital

“…In the present study, we applied ERIC-PCR to establish genetic relationships among unrelated strains of S. agalactiae (Indian isolates) and to validate its usefulness as a rapid and adequate genotyping tool. Extraction of genomic DNA: Total genomic DNA was extracted from bacterial cells, according to the procedure followed by Bensing BA et al [2]. In brief, cells from a single colony were inoculated in Todd-Hewitt broth and were grown overnight.…”