Project description:Streptococcus mitis is the closest relative of the major human pathogen S. pneumoniae. The 2,15 Mb sequence of the Streptococcus mitis B6 chromosome, an unusually high-level beta-lactam resistant and multiple antibiotic resistant strain, has now been determined to encode 2100 genes. The accessory genome is estimated to represent over 40%, including 75 mostly novel transposases and IS, the prophage phiB6 and another seven phage related regions. Tetracycline resistance mediated by Tn5801, and an unusual and large gene cluster containing three aminoglycoside resistance determinants have not been described in other Streptococcus spp. Comparative genomic analyses including hybridization experiments on a S. mitis B6 specific microarray reveal that individual S. mitis strains are almost as distantly related to the B6 strain as S. pneumoniae. Both species share a core of over 900 genes. Most proteins described as pneumococcal virulence factors are present in S. mitis B6, but the three choline binding proteins PcpA, PspA and PspC, and three gene clusters containing the hyaluronidase gene, ply and lytA, and the capsular genes are absent in S. mitis B6 and other S. mitis as well and confirm their importance for the pathogenetic potential of S. pneumoniae. Despite the close relatedness between the two species, the S. mitis B6 genome reveals a striking X-alignment when compared with S. pneumoniae.
Project description:Streptococcus mitis has emerged as one of the leading causes of bacterial endocarditis and is related to Streptococcus pneumoniae. Antibiotic resistance has also increased among strains of S. mitis and S. pneumoniae. Phages are being reinvestigated as alternatives to antibiotics for managing infections. In this study, the two virulent phages Cp-1 (Podoviridae) and Dp-1 (Siphoviridae), previously isolated from S. pneumoniae, were found to also infect S. mitis. Microbiological assays showed that both pneumophages could not only replicate in S. mitis but also produced more visible plaques on this host. However, the burst size and phage adsorption data were lower in S. mitis as compared to S. pneumoniae. A comparison of the genomes of each phage grown on both hosts produced identical nucleotide sequences, confirming that the same phages infect both bacterial species. We also discovered that the genomic sequence of podophage Cp-1 of the Félix d'Hérelle collection is different than the previously reported sequence and thus renamed SOCP.
Project description:Streptococcus mitis Nm-65 is a human commensal streptococcal strain of the mitis group that was isolated from the tooth surface of a patient with Kawasaki disease. The complete genome sequence of Nm-65 was obtained by means of hybrid assembly, using two next-generation sequencing data sets. The final assembly size was 2,085,837 bp, with 2,039 coding sequences.
Project description:Streptococcus pneumoniae's polysaccharide capsule is an important virulence factor; vaccine-induced immunity to specific capsular polysaccharide effectively prevents disease. Serotype 1 S. pneumoniae is rarely found in healthy persons, but is highly invasive and a common cause of meningitis outbreaks and invasive disease outside of the United States. Here we show that genes for polysaccharide capsule similar to those expressed by pneumococci were commonly detected by polymerase chain reaction among upper respiratory tract samples from older US adults not carrying pneumococci. Serotype 1-specific genes were predominantly detected. In five oropharyngeal samples tested, serotype 1 gene belonging to S. mitis expressed capsules immunologically indistinct from pneumococcal capsules. Whole genome sequencing revealed three distinct S. mitis clones, each representing a cps1 operon highly similar to the pneumococcal cps1 reference operon. These findings raise important questions about the contribution of commensal streptococci to natural immunity against pneumococci, a leading cause of mortality worldwide.
Project description:BACKGROUND:In streptococci of the mitis group, competence for natural transformation is a transient physiological state triggered by competence stimulating peptides (CSPs). Although low transformation yields and the absence of a widespread functional competence system have been reported for Streptococcus mitis, recent studies revealed that, at least for some strains, high efficiencies can be achieved following optimization protocols. To gain a deeper insight into competence in this species, we used RNA-seq, to map the global CSP response of two transformable strains: the type strain NCTC12261T and SK321. RESULTS:All known genes induced by ComE in Streptococcus pneumoniae, including sigX, were upregulated in the two strains. Likewise, all sets of streptococcal SigX core genes involved in extracellular DNA uptake, recombination, and fratricide were upregulated. No significant differences in the set of induced genes were observed when the type strain was grown in rich or semi-defined media. Five upregulated operons unique to S. mitis with a SigX-box in the promoter region were identified, including two specific to SK321, and one specific to NCTC12261T. Two of the strain-specific operons coded for different bacteriocins. Deletion of the unique S. mitis sigX regulated genes had no effect on transformation. CONCLUSIONS:Overall, comparison of the global transcriptome in response to CSP shows the conservation of the ComE and SigX-core regulons in competent S. mitis isolates, as well as species and strain-specific genes. Although some S. mitis exhibit truncations in key competence genes, this study shows that in transformable strains, competence seems to depend on the same core genes previously identified in S. pneumoniae.
Project description:Our group recently transcriptomically characterized coculture growth between Streptococcus mutans and several species of commensal streptococci (Rose et al, 2023; Choi et al 2024). One interaction that stood out was with Streptococcus mitis ATCC 49456, which completely inhibited the growth of S. mutans during biofilm formation. This is due to abudant hydrogen peroxide production by S. mitis ATCC 49456, 3-5x higher than other oral commensal streptococci we have worked with. To understand how the transcriptome of S. mutans is modified in coculture with a high hydrogen peroxide producer, we evaluated the transcriptome during monoculture or coculture growth between the two strains. Our results show differential gene expression (DEGs) in S. mutans that follows other trends we have documented previously with other commensal Streptococcus species, as well as DEGs specific to the interaction with S. mitis.
Project description:Antimicrobial resistance was characterized for 14 strains of Streptococcus mitis. HinfI restriction fragment length mapping of gyrA PCR amplicons from three ciprofloxacin-resistant isolates correlated with mutations associated with such resistance in other organisms. By using PCR, seven erythromycin-resistant strains were found to possess either the mef or ermB gene. Hybridization revealed tet(M) in seven tetracycline-resistant isolates.