Pneumococcus vs Viridans streptococci- 12 Major Differences
Streptococcus pneumoniae and Viridans streptococci are two groups of gram-positive bacteria that belong to the genus Streptococcus. They are both spherical or ovoid in shape and form chains or pairs when they grow. They are also both facultative anaerobes, meaning they can grow with or without oxygen. However, they have different characteristics and roles in human health and disease.
Streptococcus pneumoniae, also known as pneumococcus, is a major cause of pneumonia, meningitis, otitis media, sinusitis, and septicemia. It is one of the most common bacterial pathogens in humans and can affect people of all ages. It has a polysaccharide capsule that protects it from phagocytosis and helps it adhere to host cells. It also produces several virulence factors, such as pneumolysin, autolysin, and hydrogen peroxide, that damage host tissues and immune cells. It is classified into more than 90 serotypes based on the antigenic variation of its capsule.
Viridans streptococci are a heterogeneous group of streptococci that are normally found in the oral cavity, gastrointestinal tract, genitourinary tract, and skin of humans. They are usually harmless commensals that do not cause disease in healthy individuals. However, they can become opportunistic pathogens when they enter the bloodstream or other sterile sites, especially in immunocompromised or debilitated patients. They can cause endocarditis, bacteremia, abscesses, and dental caries. They are classified into six groups based on their biochemical and phenotypic properties: anginosus group, mitis group, mutants group, salivarius group, bovis group, and sanguinis group.
In this article, we will compare and contrast the properties of Streptococcus pneumoniae and Viridans streptococci and highlight the 12 major differences between them.
Streptococcus pneumoniae and Viridans streptococci are both gram-positive cocci that belong to the genus Streptococcus. They share some common features, such as being catalase-negative, alpha-hemolytic, and facultative anaerobes. However, they also have distinct characteristics that can help to differentiate them from each other.
One of the most reliable methods to distinguish Streptococcus pneumoniae from Viridans streptococci is the optochin susceptibility test. Optochin is a chemical agent that inhibits the growth of Streptococcus pneumoniae but not Viridans streptococci. Therefore, if a bacterial culture is exposed to optochin on a blood agar plate, Streptococcus pneumoniae will show a zone of inhibition around the optochin disk, while Viridans streptococci will grow normally.
Another method to differentiate Streptococcus pneumoniae from Viridans streptococci is the bile solubility test. Bile is a digestive fluid that contains bile salts, which can lyse the cell wall of Streptococcus pneumoniae but not Viridans streptococci. Therefore, if a bacterial culture is treated with bile or sodium deoxycholate, Streptococcus pneumoniae will be dissolved, and the culture will become clear, while Viridans streptococci will remain intact and the culture will remain turbid.
A third method to differentiate Streptococcus pneumoniae from Viridans streptococci is the capsule detection test. Streptococcus pneumoniae has a polysaccharide capsule that protects it from phagocytosis and enhances its virulence. Viridans streptococci do not have a capsule or have a very weak one. Therefore, if a bacterial culture is stained with a capsule-specific dye such as India ink or Quellung reagent, Streptococcus pneumoniae will show a halo around the cells, while Viridans streptococci will not.
A fourth method to differentiate Streptococcus pneumoniae from Viridans streptococci is the molecular identification test. Streptococcus pneumoniae and Viridans streptococci have different genetic profiles that can be detected by techniques such as PCR, DNA hybridization, or sequencing. For example, Streptococcus pneumoniae has a unique gene called ply that encodes for pneumolysin, a toxin that damages host cells and tissues. Viridans streptococci do not have this gene or have a different version of it. Therefore, if a bacterial DNA sample is amplified with ply-specific primers or probed with ply-specific probes, Streptococcus pneumoniae will produce a positive signal, while Viridans streptococci will not.
These are some of the main methods to differentiate Streptococcus pneumoniae from Viridans streptococci based on their phenotypic and genotypic features. However, it is important to note that these methods are not always conclusive or applicable in every situation. Therefore, it is advisable to use a combination of methods and consult with an expert microbiologist for accurate identification and diagnosis.
Pneumococcus and Viridans streptococci are both gram-positive cocci that belong to the genus Streptococcus. However, they have many differences in their morphology, physiology, pathogenicity, and clinical significance. Here are 12 major differences between Pneumococcus and Viridans streptococci:
- Shape and arrangement: Pneumococcus is usually lancet-shaped and occurs in pairs or short chains. Viridans streptococci are round or oval and occur in long chains or clusters.
- Capsule: Pneumococcus has a polysaccharide capsule that is essential for its virulence and protects it from phagocytosis. Viridans streptococci are either non-capsulated or have a thin capsule that is not involved in virulence.
- Hemolysis: Pneumococcus produces alpha-hemolysis on blood agar, which means it partially lyses the red blood cells and produces a greenish discoloration around the colonies. Viridans streptococci also produce alpha-hemolysis, but some strains can produce beta-hemolysis (complete lysis of red blood cells) or gamma-hemolysis (no lysis of red blood cells).
- Optochin sensitivity: Pneumococcus is sensitive to optochin, which is an antibiotic that inhibits its growth. Viridans streptococci are resistant to optochin and grow normally in its presence.
- Bile solubility: Pneumococcus is soluble in bile, which means it can be lysed by bile salts, and its colonies disappear when exposed to bile. Viridans streptococci are insoluble in bile and remain intact when exposed to bile.
- Quellung reaction: Pneumococcus shows a positive quellung reaction, which means its capsule swells and becomes visible when treated with specific antisera. Viridans streptococci do not show a quellung reaction because they either lack a capsule or have a thin one that does not react with antisera.
- Lancefield grouping: Pneumococcus does not belong to any Lancefield group, which is a classification system based on the antigenic properties of the cell wall carbohydrates of streptococci. Viridans streptococci belong to various Lancefield groups, such as A, B, C, D, F, G, H, K, L, M, N, O, S, V, and X.
- Biochemical reactions: Pneumococcus can ferment glucose and maltose but not lactose or sucrose. It also produces hydrogen peroxide and is catalase-negative. Viridans streptococci can ferment various sugars depending on the species and strain. They also produce hydrogen peroxide but are catalase-negative.
- Pathogenicity: Pneumococcus is a major human pathogen that causes pneumonia, meningitis, otitis media, sinusitis, septicemia, and other infections. It has several virulence factors, such as capsule, pneumolysin, autolysin, teichoic acid, peptidoglycan, IgA protease, and adherence factors. Viridans streptococci are normal commensals of the oral cavity and upper respiratory tract but can cause opportunistic infections such as dental caries, endocarditis, abscesses, bacteremia, and meningitis. They have fewer virulence factors than pneumococcus and mainly rely on their ability to adhere to host tissues and form biofilms.
- Antibiotic resistance: Pneumococcus has developed resistance to many antibiotics such as penicillin, erythromycin, tetracycline, chloramphenicol, and fluoroquinolones due to mutations in its genes or acquisition of plasmids or transposons. Viridans streptococci have also developed resistance to some antibiotics, such as penicillin and erythromycin but are generally more susceptible than pneumococcus.
- Vaccination: Pneumococcus can be prevented by vaccination with pneumococcal conjugate vaccine (PCV) or pneumococcal polysaccharide vaccine (PPV), which contain purified capsular antigens of the most common serotypes of pneumococcus. Viridans streptococci do not have a specific vaccine but can be prevented by maintaining good oral hygiene and avoiding invasive procedures that can introduce them into the bloodstream.
- Clinical diagnosis: Pneumococcus can be diagnosed by culture of sputum or other specimens on blood agar or chocolate agar followed by an optochin sensitivity test or quellung reaction test. It can also be detected by polymerase chain reaction (PCR) or antigen detection tests in urine or cerebrospinal fluid (CSF). Viridans streptococci can be diagnosed by culture of blood or other specimens on blood agar followed by biochemical tests or Lancefield grouping tests. They can also be detected by PCR or DNA hybridization tests.
These are some of the major differences between Pneumococcus and Viridans streptococci that can help in their identification and treatment.
In this article, we have compared and contrasted two groups of streptococci: Streptococcus pneumoniae (pneumococcus) and viridans streptococci. These are both gram-positive, alpha-hemolytic, and catalase-negative cocci that can cause various infections in humans. However, they have some important differences that can help us to identify and treat them appropriately. Here is a summary of the 12 major differences between pneumococcus and viridans streptococci:
| Pneumococcus | Viridans streptococci |
| ------------ | -------------------- |
| Encapsulated | Non-encapsulated |
| Lancefield group not expressed | Lancefield groups C, F, G, S or not expressed |
| Optochin sensitive | Optochin resistant |
| Bile soluble | Bile insoluble |
| Quellung reaction positive | Quellung reaction negative |
| Autolysin present | Autolysin absent |
| Mitis group | Mitis, salivarius, anginosus, mutants, and Bovis groups |
| Common cause of pneumonia, otitis media, meningitis, and sepsis | Common cause of endocarditis, dental caries, and bacteremia |
| Found in the nasopharynx of 5-10% of healthy adults | Found in the oral cavity of 80-90% of healthy adults |
| Vaccine available | No vaccine available |
| Penicillin susceptible (some strains resistant) | Penicillin resistant (some strains susceptible) |
| Beta-lactamase production rare | Beta-lactamase production common |
We hope this article has helped you to understand the similarities and differences between pneumococcus and viridans streptococci. If you have any questions or comments, please feel free to leave them below. Thank you for reading!
- Comparison of properties between Pneumococcus and Viridans streptococci
Pneumococcus and Viridans streptococci are both gram-positive cocci that belong to the genus Streptococcus, but they have many differences in their properties and clinical significance. Here are 12 major differences between them:
| Property | Pneumococcus | Viridans streptococci |
| --- | --- | --- |
| Capsule | Present and essential for virulence | Absent or poorly developed |
| Optochin sensitivity | Sensitive (except some resistant strains) | Resistant |
| Bile solubility | Soluble (lysed by bile salts) | Insoluble |
| Quellung reaction | Positive (capsule swells when exposed to specific antisera) | Negative |
| Hemolysis on blood agar | Alpha-hemolytic (partial hemolysis) | Alpha-hemolytic or non-hemolytic |
| Lancefield group antigen | None | Various (A, C, D, F, G, etc.) |
| Biochemical reactions | Ferment inulin and produce acid from mannitol | Do not ferment inulin and do not produce acid from mannitol |
| Genomic features | Has a unique gene cluster (psrP-secY2A2) that is absent in Viridans streptococci | Lacks the psrP-secY2A2 gene cluster |
| Pathogenicity | Highly pathogenic and causes pneumonia, meningitis, otitis media, sinusitis, septicemia, etc. | Low virulence and mainly causes dental caries, endocarditis, abscesses, etc. |
| Colonization site | Nasopharynx | Oral cavity and upper respiratory tract |
| Transmission mode | Respiratory droplets or direct contact with carriers | Saliva or dental procedures |
| Prevention and treatment | Vaccination (pneumococcal conjugate vaccine or pneumococcal polysaccharide vaccine) and antibiotics (penicillin, cephalosporins, macrolides, etc.) | Good oral hygiene and antibiotics (penicillin, vancomycin, etc.) |
These are some of the main differences between Pneumococcus and Viridans streptococci that can help in their identification and management. However, there may be some variations and exceptions among different strains and species of these bacteria. Therefore, it is important to perform laboratory tests and consult a physician for accurate diagnosis and treatment.
- Capsule: The capsule is a polysaccharide layer that surrounds the cell wall of some bacteria and protects them from phagocytosis and complement-mediated lysis. Pneumococcus has a thick capsule that is composed of 90 different serotypes and is the main virulence factor of this organism. Viridans streptococci are generally non-encapsulated or have a thin capsule that is not antigenically diverse. The presence or absence of a capsule can be detected by staining the bacteria with India ink or methylene blue and observing them under a microscope. Pneumococcus will appear as round or oval cells surrounded by a clear halo, while viridans streptococci will appear as chains of cells without a halo.
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