Streptococcus salivarius

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A Microbial Biorealm page on the genus Streptococcus salivarius

Contents

Classification

Higher order taxa

Bacteria; Firmicutes; Bacilli; Lactobacillales; Streptococcaceae; Streptococcus; Streptococcus salivarius

Species

NCBI: Taxonomy

Streptococcus salivarius

Description and significance

Streptococcus salivarius is the principal commensal bacterium of the oral cavity in humans. S. salivarius is a normal inhabitant of the upper respiratory tract. It may enter the blood stream by accident during dental work or when brushing the teeth. It is the first bacterium which colonizes the dental plaque, before being joined by numerous other species of various genera [6]. It therefore seems to be the pioneer in colonizing dental plaque, it creates favorable conditions so other species can begin to colonize. It is also a bacterium which plays the role of moderator, permitting the implantation of bacteria which are harmful to the health of the oral cavity.

Better knowledge of the molecular and physiologic factors which allow it to colonize dental plaque and to interact with other species will help in designing strategies for the prevention of cavities, especially in children [6]. Also, greater knowledge of this organism can help with research on mouth odor.

Moreover, when this bacterium enters the bloodstream it is found that it may cause septicemia in neutropenic patients, a condition that shows a abnormal low level amounts of neutrophils in the blood. Neutrophils are also known as white blood cells and are involved in the body’s immune response to infections [5]. Also, Streptococcus salivarius is used to treat patients with atypical pneumonia, which is an illness of the lungs where they become flooded with fluid.

Genome structure

Not much is known about the genome of Streptococcus salivarius other than its genome size is estimated to be 1800kb long. Its genome is yet to be sequenced [7], but it is in progress. A closely related species of S. salivarius, S. thermophilus has been sequenced. Its genome size has been determined to be 1796kb on a single circular chromosome [8]. S. thermophilus is a lactic acid bacterium used for making milk and yogurt in the dairy industry. It was important to sequence S. thermopilus because it is phylogenetically close to pathogenic streptococci. The genome was sequenced using random shotgun sequencing and followed up by multiplex PCR [8].

S. thermophilus has a 39% G-C content, 6 Ribosomal RNA's, and 67 tRNA's [8]. It is also known that 10% of the genes are not functional due to frameshifts, nonsense mutations, deletions, or pseudogenes. Frameshifts can occur in a genome when one or two nucleotides are deleted or inserted next to each other. This would cause a shift in the reading frame, the frame in which DNA gets transcribed into RNA. A pseudogene is a gene where it becomes transcribed and translated but it has no functional capabilities. Moreover, 30% of their genome is dedicated to energy metabolism and 60% to atypical, phages, and transposons [8]. Transposons are given the name "jumping genes" or mobile genetic elements because of their ability to move around in the genome. They may cause mutation and they may increase the amount of DNA in the genome.

Cell structure and metabolism

S. salivarius is a Gram-positive cocci, which means in a gram stain test it would stain purple. Gram-positive bacteria have a single plasma membrane followed by periplasmic space and a thick peptidoglycan layer called murein. Other than protection the murein layer also helps in the shape and rigidity of the bacteria. Murein is a polymer which is unique to bacteria, this is the reason why it is a good target for antibiotics. Moreover, the murein layer allows the bacteria to survive in media with osmotic pressure less than that of their cytoplasm [10]. S. salivarius is approximately 2 µm in length. The cocci usually occur in pairs and short chains. They are facultative anaerobes and either non- or alpha hemolytic on blood agar [5]. Blood agar is used in labs to detect hemolytic activity.

S. salivarius contains fimbriae on their cell surface. Fimbriae are hair-like appendages that are composed of protein subunits with diameters ranging from 2-8 nm. Fimbriae are involved in co-aggregation of S. salivarius with the periodontopathogen Prevotella intermeida [2].

Ecology

The hydrolysis of urea by urease enzymes of oral bacteria like Streptococcus salivarius has a major impact on oral microbial ecology and is involved in oral health and diseases. The ability to genetically engineer plaque bacteria that can modulate environmental pH through ureolysis will open the way to using S. salivarius to test hypotheses regarding the role of oral ureolysis in dental caries, calculus formation, and periodontal diseases. This organism may eventually prove useful for controlling dental caries by replacement therapy [1].

Pathology

Diseases may be caused if S. salivarius enters the blood stream. This may occur during dental work or brushing of the teeth. S. salivarius may cause septicemia in neutropenic patients. Septicemia is a systemic disease caused by pathogenic organisms or their toxins in the blood stream, it is also known simply as blood poisoning.

Streptococcuss salivarius is infrequently pathogenic. Viridans streptococci species cause most dental caries and are the most frequent cause of subacute native valve bacterial endocarditis, typically associated with dental procedures [9]. Endocaritis is an inflammation of the inner layer of the heart, the endocardium. The severity of the disease is typically based on the microorgansim involved. In the case of Streptococci the disease is labeled as subacute bacterial endocarditis, which is due to the bacterias low virulence, but in the case of the acute bacterial endocarditis it is caused by Staphylococcus aureus which has a much greater virulence [9].

Application to Biotechnology

Streptococcus salivarius secretes a glucosltransferase (Gtf) which forms a glucan from sucrose. S. salivarius is one of the main sources of Gtf in saliva and in the acquired pellicle is believed to be from S. salivarius resident on the dorsum of the tongue. Gtfs incorporated in the pellicle are known to be active and to form glucans to which other oral streptococci, such as the mutans streptococci, are able to adhere. Thus, Gtfs produced by S. salivarius at sites distant from the tooth surface may aid in the initial attachment or entrapment of other oral species on newly erupted tooth surfaces or on tooth surfaces following prophylaxis. [4]

S. salivarius is also known to secrete an enzyme called urease. Urease can catalyze the hydrolysis of urea to ammonia and carbon dioxide [1].

Current Research

A new research found results that suggest Gram-positive micro-organisms such as S. salivarius contribute to oral malodor production by deglycosylating salivary glycoproteins, thus exposing their protein core to further degradation by Gram-negative micro-organisms. Studies show a direct link between levels of Streptococcus salivarius in the mouth, throat and tonsils and the development of halitosis [3]. Current research is being done to better understand mouth odor in relation to S. salivarius.

Also as mentioned previously in the Ecology section, further studies are being performed to be able to prevent dental caries.

References

[1] Chen, YY. "Streptococcus salivarius urease: genetic and biochemical characterization and expression in a dental plaque streptococcus." Infection and Immunity.1996.Volume 64 No.2. p. 585-592.

[2] Lévesque, Céline, ChristianVadeboncoeur, and MichelFrenette. "The csp operon of Streptococcus salivarius encodes two predicted cell-surface proteins, one of which, CspB, is associated with the fimbriae". Microbiology 150.2004. (Pt 1). p. 189-98.

[3] N. Sterer1, and M. Rosenberg "Streptococcus salivarius Promotes Mucin Putrefaction and Malodor Production by Porphyromonas gingivalis".2006.Journal of Dental Reserach. p. 910-914.

[4] Simpson, CL. "Streptococcus salivarius ATCC 25975 Possesses at Least Two Genes Coding for Primer-Independent Glucosyltransferases".Infection and Immunity.1995.Volume 63 No.2. p. 609-621.

[5] "MATERIAL SAFETY DATA SHEET - INFECTIOUS SUBSTANCES". "Public Health Agency of Canada". 2001.

[6] Streptococcus salivarius JIM8777, JIM8780: The principal inhabitant of the human oral cavity. Genoscope - Centre National de Séquençage. http://www.cns.fr/externe/English/Projets/Projet_MB/organisme_MB.html.

[7] Chastanet, A. "clpP of Streptococcus salivarius Is a Novel Member of the Dually Regulated Class of Stress Response Genes in Gram-Positive Bacteria." Journal of bacteriology.2003.Volume 185 No.2. p.683-687.

[8] Bolotin, A "Complete sequence and comparative genome analysis of the dairy bacterium Streptococcus thermophilus". Nature biotechnology.2004.Volume 22 No. 12. p. 1554-1558.

[9] White, J C, and C FNiven. "Streptococcus s.b.e.: A Streptococcus Associated with Subacute Bacterial Endocarditis." Journal of bacteriology.1946. Volume 51 No. 6. p. 717-22.

[10] Schaechter, M, Ingraham, L. J, Neidhardt,C. F."Microbe". Washington: ASM Press, 2006. p.23-25

Edited by Artin Meserkhani, a student of Rachel Larsen and Kit Pogliano

KMG

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