Streptococcus salivarius

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1. Classification

a. Higher order taxa

Domain: Bacteria
Phylum: Firmicutes
Class: Bacilli
Order: Lactobacillales
Family: Streptococcaceae
Genus: Streptococcus
Species: Streptococcus salivarius

2. Description and significance

S. salivarius is a spherical, Gram-positive, facultative anaerobic commensal bacterium that is both catalase and oxidase negative. As one of the first colonizers of the human oral cavity, upper respiratory tract, and gut after birth, S. salivarius is thought to contribute to immune homeostasis and regulate inflammatory response. Thus, the bacterium is most often harmless but considered an opportunistic pathogen (1).

Humans are introduced to S. salivarius within a few hours after birth, inhabiting the mouth and upper respiratory tract, making it one of the first commensal bacteria humans are exposed to (2). Early exposure allows humans to acquire immunity, so S. salivarius is usually considered harmless. However, while immunity is established during infancy, the bacteria are opportunistic pathogens, proving to be detrimental under certain circumstances, such as entrance to the bloodstream (3). Due to its opportunistic nature, S. salivarius has been linked to cases of sepsis in immunocompromised patients with neutropenia, a disease associated with a depleted level of white blood cells in the body (3).

3. Genome structure

The entire genome structure of a clinical strain CCHSS3 of S. salivarius was sequenced using the Sanger shotgun method to produce a draft of the genome, and Next Generation Sequencing was used to revise and correct any sequencing errors (4). The initial draft was assembled into 374 contigs, which were then ordered and gaps were closed. Finally, IS boundaries were sequenced, and mismatch and small corrections were carried out by SOLiD sequencing technology with 110-fold coverage to ensure correct assembly and sequence accuracy (4). The circular chromosome of S. salivarius CCHSS3 consists of 2.2 million base pairs with a GC-content of 40% (4). It comprises of 2032 genes, with 2027 that encode for proteins; there are also 68 tRNA genes that encompass all the amino acids, and 6 rRNA operons (4).
There is a complete genome sequence available for the S. salivarius strain JIM8777. The genome of the strain JIM8777 consists of genes that help regulate the oral community. These genes include those involved in lactose uptake, urea catabolism, and bacteriocin production. (5)
The sequencing of the S. salivarius genome revealed a gene similar to the stress resistance gene ClpP in Escherichia coli. Stress resistance genes encode for stress-induced proteins such as chaperones that help refold denatured proteins or proteases that degrade them; these proteins allow the bacteria to survive under stress. ClpP is also found in several other bacteria, including Yersinia enterocolitica and Pseudomonas fluorescens, and was shown to have slightly different functions, such as conferring virulence and participating in biofilm formation (1). ClpP is found to be under the regulation of two repressor proteins, CtsR and HrcA. A study led by Chastanet and Msadek showed that repression is lifted during growth in high temperatures, allowing the production of heat-shock proteins from the clpP gene (1). It is unknown whether the similar gene found in S. salivarius have the same heat-resistant properties. Therefore, additional research would be helpful in determining whether S. salivarius is able to thrive at relatively high temperatures, which makes the bacteria more difficult to exterminate with high heat alone.

4. Cell structure

S. salivarius is a Gram-positive cocci so Gram stain results would show a purple stain under the microscope due to crystal-violet dye’s affinity to the thick peptidoglycan layer. S. salivarius contains a peptidoglycan layer specifically called murein, which provides protection and rigidity, and helps shape the cell. Murein is a characteristic polymer of bacteria making it a good target for antibiotics.

5. Metabolic processes

S. salivarius is a facultative anaerobe (6). Facultative anaerobes perform respiration in the presence of oxygen. In situations where oxygen is not readily available, facultative anaerobes can switch to fermentation or anaerobic respiration to generate ATP. Since food from the host enters the oral cavity, the amount of nutrients that S. salivarius, as well as other bacteria residing in the oral cavity, are essentially non-limiting. S. salivarius strain JIM8777 was found to contain a gene conferring lactose catabolism (5), which allows the bacteria to thrive in areas such as the oral cavity where such sugars can be found.

6. Ecology

S. salivarius is found in the upper respiratory tract and oral cavity of the human body. While the bacterium is part of the normal flora in those environments, its entrance to the bloodstream causes it to become pathogenic (3).
Several strains of S. salivarius are able to interfere with respiratory pathogens and metabolites present in S. salivarius can trigger inhibition of NF-κB activation in human IECs (2). Specific strains of S. salivarius, such as S. salivarius TOVE-R and K12, have been reported to be successful antagonists of virulent streptococci, which has been attributed to its bacteriocin production (2). S. salivarius K12’s production of bacteriocins show inhibitory activity against halitosis-associated species (7). Different strains of S. salivarius are capable of producing bacteriocins called lantibiotics. Lantibiotics have the potential to treat infectious diseases and thus further research on how S. salivarius can act as a probiotic can lead to new discoveries of treatments in medicine. (8)

7. Pathology

How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

7. Key microorganisms

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8. Current Research

Include information about how this microbe (or related microbes) are currently being studied and for what purpose

9. References

It is required that you add at least five primary research articles (in same format as the sample reference below) that corresponds to the info that you added to this page. [Sample reference] Faller, A., and Schleifer, K. "Modified Oxidase and Benzidine Tests for Separation of Staphylococci from Micrococci". Journal of Clinical Microbiology. 1981. Volume 13. p. 1031-1035.