Content Writer-SME
Streptococcus are common pathogens belongs to the family Streptococcacea and is a genus of gram-positive bacteria. The shape and arrangement of streptococcus bacteria is very unique and resembles a bead or chain like structure. There are different species of S treptococcus some of which are beneficial to humans while others are infectious. For example, S. thermophilus is utilized as probiotics which is essential for the gut health of humans, whereas S.pyogenes causes infections such as impetigo, scarlet fever, tonsilitis, pneumonia, and strep throat.
Streptococcus Species
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Streptococcus are spherical-shaped bacteria that are found either in pairs or chains. These bacteria are non-motile and non-spore-forming. Almost every species of streptococci bacteria possesses different characteristic features. Some of them cause diseases to both humans and animals, while others are used in the manufacturing of fermented food products.
- The cell division in streptcoccus species results into chain formation.
- Species of streptococci bacteria for example S.agalactiae cause blood poisoning in newborn children.
- Other species like S.lactis and S.cremoris are used in the production of dairy products like cheese, curd, etc.
- Streptococcus species exists as three forms- Catalase negative, Oxidase negative, and facultative anaerobes.
Classification of Streptococcus Species
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Classification of Streptococcus bacteria is done on six important parameters:
- Requirement of oxygen
- Brown Classification
- Sherman’s Classification
- Lancifield Classification
- 16sRNA sequence.
Requirement of Oxygen
On the basis of oxygen requirement, streptococcus is classified as:
- Facultative anaerobes (able to survive with or without oxygen). For eg: Streptococcus spp.
- Obligate anaerobes (able to live without oxygen). For eg: Peptostreptococcus.
Brown Classification
Brown classification is done based on the hemolytic pattern on sheep blood agar.
- Alpha-hemolysis Group: An incomplete hemolysis takes place and shows a green discoloration around the colony. For example, Streptococcus pneumoniae.
- Beta-hemolysis Group: A complete lysis of red blood cells takes place and shows a clear zone around the colony. For example, Streptococcus pyogenes.
- Gamma-hemolysis Group: no lysis of red blood cells takes place. For example, streptococcus faecalis.
Sherman's Classification
This classification is based on the physiological features of streptococcus.
- Enterococci: They belong to the gamma hemolytic group or non-hemolytic group and are present in the human intestine.
- Lactococci: They belong to the gamma hemolytic group and are present in dairy products.
- Vridans Streptococci: They belong to the Alpha hemolytic group and are present in the upper respiratory tract of humans.
Lancified Classification
Lancified classification is also called serological classification and is divided into the following groups.
- Group A, B, and C: They belong to the Beta-hemolytic group. For example, Streptococcus pyogenes, Streptococcus agalactiae, and Streptococcus equisimitis respectively.
- Group D: They belong to the Alpha or gamma hemolytic group. For example, Enterococcus.
16sRNA Classification
The classification of streptococcus is based on the analysis of the 16sRNA sequence is as follows:
- Pyogenic group
- Salivarious group
- Anginosius group
- Bovis group
- Mutants group
- Mitis group
Classification of Streptococcus (Based on the 16sRNA sequence)
Characteristics of Streptococcus Species
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Every species of streptococcus bacteria possesses different characteristic features. They differ in shape, size, arrangement, motility, media type, colony formation, pH, etc. The table below shows the morphology characteristics of streptococcus:
| Characteristics | Description |
|---|---|
| Shape | Spherical in shape |
| Size | 0.5 - 1 µm |
| Gram Staining | Gram-positive bacterium |
| Cell Arrangement | Arranged in chains |
| Motility | Non-motile bacterium |
| Spores | Non-Spore forming |
| Types | Group A, Group B, Group C, Group D |
| Growth Medium | Blood Agar |
| Optimum pH | 7.4 to 7.6 |
Things to Remember
- Streptococcus species are an important member of gram-positive bacteria.
- Streptococcus pneumoniae is the pathogen responsible for causing pneumonia in humans.
- Strep disease and infections may sometimes become severe and can also cause death.
- Streptococcus thermphilus can also be utilized as probiotics.
- The disease caused by streptococcus species can be treated by antibiotics.
Sample Questions
Ques. Write any three characteristics of Streptococcus. (2 marks)
Ans. The two main characteristics of Streptococcus bacteria are:
- These bacteria can survive in low and high oxygen concentrations.
- Streptococci are halotolerant.
- It can grow at a temperature of 37℃.
Ques. What are the two Streptococcus species based on hemolytic properties? (2 marks)
Ans. The types of streptococcus species are based on their hemolytic properties:
- Alpha hemolytic streptococcus causes respiratory tract infections. Example: S.pneumoniae.
- Beta hemolytic streptococcus are further divided into two types: group A and group B.
Ques. What infections are caused by Group A and B streptococcus? (3 marks)
Ans. Group A and Group B are the types of streptococcus bacteria.
- Group A streptococcus causes strep throat and impetigo.
- Infections caused by this group can be invasive or sometimes fatal.
- This includes Streptococcus pyogenes.
- Group B streptococcus causes severe invasive infections in newborns like meningitis.
- An example of Group B streptococcus is, Streptococcus agalactiae.
Ques. What is your understanding of the process of hemolysis? (3 marks)
Ans. The process of destruction of old red blood cells is called hemolysis.
- In hemolysis, the damaged or old red blood cells are replaced with the new ones.
- Hemolysis can occur by Streptococcus species.
- The hemolytic reactions are observed on a blood agar plate.
Ques. What are the complications caused by streptococcus pyogenes? (2 marks)
Ans. The complications caused by streptococcus pyogenes are:
- Rheumatic fever
- Glomerulonephritis
- Pneumonia
- Scarlet fever
- Bacteremia
Ques. Based on gram staining the bacteria is classified into which two groups? (3 marks)
Ans. Bacteria are classified into gram-positive and gram-negative bacteria.
- Gram-positive bacteria possess a thick cell wall that retains the crystal violet stain.
- Gram-negative bacteria have a thin cell wall that does not retain the crystal violet stain.
Ques. What is the purpose of gram staining? Give some examples of gram-positive and gram-negative bacteria. (2 marks)
Ans. Gram staining was introduced by scientist Hans Christian Brown in the year 1884. This method is used to identify gram-positive and gram-negative bacteria based on their cell wall composition.
- Examples of gram-positive bacteria are Streptococcus, Staphylococcus, and Enterococcus.
- Examples of gram-negative bacteria are Escherichia coli, Enterobacter, Pseudomonas, and Shigella.
Ques. What is the sugar fermentation test? (2 marks)
Ans. A sugar fermentation test helps to identify the fermentation pattern of bacteria.
- This test is also used to determine the ability of bacteria to ferment different types of sugars.
- The sugar fermentation test determines the presence of acid or a gas produced from this test.
- The sugars or carbohydrates used as a medium are lactose, glucose, or sucrose.
Ques. What is strep throat? Write its symptoms. (2 marks)
Ans. Strep throat is a bacterial throat infection caused by group A streptococcus also called Streptococcus pyogenes. The symptoms of strep throat are:
- Difficulty in swallowing
- Swelling of tonsils
- High fever
- Body ache
- Vomiting
Ques. What medications are taken to treat streptococcal infections? How are these infections diagnosed? (2 marks)
Ans.Antibiotics like penicillin, amoxanswersn, and benzathine are taken to treat streptococcal infections.
- These infections are usually diagnosed by a blood test, or biopsy.
- Sometimes, a CT scan is used to look for any damage caused by such infections.
Ques. Answer the following questions: (2 marks)
- What are the arrangements of a cocci bacteria?
-
Who coined the term ‘Streptococcus”?
Ans. The answer of the questions are given below:
- Cocci means “spherical”. The cocci bacteria is present in pairs, groups, chains, or in a single form.
- The term ‘Streptococcus’ was introduced by physician Albert Theodore Billroth in the year 1877.
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