Analysis of Streptococcus pneumoniae sequenced genomes revealed a region present only in selected strains consisting of two ORFs: a putative cell wall anchored protein and a putative transcriptional regulator. The cell wall anchored protein contains large regions of collagen-like repeats, the number of which varies between strains. We have therefore named this protein PclA for pneumococcal collagen-like protein A. The second gene, spr1404, encodes a putative transcriptional regulator. We examined the strain distribution of these two genes among a collection of clinical isolates from invasive pneumococcal disease and found them to be present in 39% of the strains examined. Strains were either positive for both genes or lacked both, with the two genes always present together in the same location of the genome. RT-PCR analysis revealed that pclA is transcribed in vitro, even in the absence of spr1404. Single deletion mutants lacking either gene were not attenuated in a mouse model of invasive pneumonia. However, the pclA mutant was defective in adherence and invasion of host cells in vitro.

We have detected a cholesterol-dependent cytolysin, which we have named mitilysin, in a small number of Streptococcus mitis isolates. We have sequenced the mitilysin gene from seven isolates of S. mitis. Comparisons with the pneumococcal pneumolysin gene show 15 amino acid substitutions. S. mitis appear to release mitilysin extracellularly. Certain alleles of mitilysin are not recognized by a monoclonal antibody raised to the related toxin pneumolysin. Based on enzyme-linked immunosorbent assay and neutralization assay results, one isolate of S. mitis may produce a further hemolytic toxin in addition to mitilysin. As genetic exchange is known to occur between S. mitis and Streptococcus pneumoniae, this finding may have implications for the development of vaccines or therapies for pneumococcal disease that are based on pneumolysin.Viridans group streptococci (VGS) are a group of closely related streptococci which includes the pneumococcus. The VGS belong to the normal upper respiratory tract and oral flora of humans (10). Oral streptococci contain a number of species of naturally transformable streptococci able to take up naked DNA from the extracellular environment (19). On the basis of 16S rRNA gene sequencing, the species most closely related to Streptococcus pneumoniae are Streptococcus mitis and Streptococcus oralis, which have over 99% sequence identity with S. pneumoniae (15). Pneumolysin (Ply) is a protein toxin produced by S. pneumoniae that belongs to a large protein family of cholesterol-dependent cytolysins (14). The family consists of 50-to 60-kDa single-chain proteins produced by at least seven gram-positive bacteria from the genera Streptococcus, Bacillus, Clostridium, Listeria, and Arcanobacterium (1). S. pneumoniae causes diseases such as pneumonia, bacteremia, meningitis, and otitis media (21), and pneumolysin is an important virulence factor of this human pathogen. Mutations in the ply gene can lead to reduced virulence of S. pneumoniae, and an isogenic mutant pneumococcus deficient in pneumolysin has been shown to be cleared from the blood following infection (5, 6). There is evidence of horizontal gene transfer between other VGS and S. pneumoniae, penicillin resistance has been transferred from the VGS to pneumococci by the transfer of penicillin binding proteins (9), and Ferrandiz et al. have suggested that VGS are donors in the horizontal transfer of fluoroquinolone resistance genes to S. pneumoniae (3, 11).Whatmore et al. studied the distribution of the ply and ply-related genes in S. pneumoniae, S. mitis, and S. oralis (27). None of the S. oralis strains tested contained plyrelated sequences, whereas some of the S. mitis strains were found to posses a pneumolysin homologue. The aim of the work reported here was to investigate the presence, nature, and activity of the cholesterol-dependent cytolysin in a collection of VGS. (CD 1,3,4,5,6, and 7), and 191 clinical isolates. The clinical strains were isolated from blood cultures (n ϭ 129 [from medical, surgical, hematology, and oncology ward...

Branching networks are ubiquitous in nature and their growth often responds to environmental cues dynamically. Using the antibiotic-producing soil bacterium Streptomyces as a model we have developed a flexible mathematical model platform for the study of branched biological networks. Streptomyces form large aggregates in liquid culture that can impair industrial antibiotic fermentations. Understanding the features of these could aid improvement of such processes. The model requires relatively few experimental values for parameterisation, yet delivers realistic simulations of Streptomyces pellet and is able to predict features, such as the density of hyphae, the number of growing tips and the location of antibiotic production within a pellet in response to pellet size and external nutrient supply. The model is scalable and will find utility in a range of branched biological networks such as angiogenesis, plant root growth and fungal hyphal networks.

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