How Does Streptococcus Cause Diseases?
If you feel pain in your throat which leads to swallowing issues then you might think of it as a common cold and sore throat. Having a sore throat could be harmless or it could indicate a more severe throat infection called streptococcus.
In general, sore throats are caused by viruses whereas strep throat is due to the streptococcus bacteria. This bacterial streptococcus infection of the throat and tonsils is caused by group A streptococcus.
The diseases caused by streptococcus bacteria could range from minor illnesses to extremely serious and fatal consequences. In this article, we will find out more about what is streptococcus, the streptococcus classification, what implications streptococcal skin infections have, and learn streptococcus pathogenesis.
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Streptococci Definition
The other names for streptococcus bacteria are GAS (Group A streptococcus) or GABHS (Group A (beta-hemolytic) streptococcus). Streptococcus are gram-positive bacteria that have an ovoid or spherical shape. They are chiefly parasitic and nonmotile bacteria that divide only in one plane and occur in chains or pairs.
Streptococcus is an organism with no nuclear membrane and has no organelles in the cytoplasm (except for ribosomes) hence its pyogenes are prokaryotes.
The genetic material of streptococcus is in the form of a single continuous chain which forms loops or coils.
These cocci are anaerobic i.e. they can live without needing oxygen and they have complex nutritional requirements.
Many of the known species of group A streptococcus are parasitic in humans as well as animals. Some of them are important pathogens.
Strep throat is not very prevalent and accounts for only a small percentage of sore throats.
If strep throat is not treated, it can cause many complications for instance rheumatic fever, kidney inflammation, etc. Rheumatic fever can give painful and inflamed joints, damage to heart valves, and rashes.
Streptococcus infection mostly occurs in children but it can be seen in adults too.
Streptococci Has Two Key Groups
\[\alpha\] (alpha)-hemolytic Streptococci
This is the most common group and many strains live inside humans without causing any symptoms.
This group is further divided into Streptococcus pneumonia and Viridans Streptococci.
\[\beta\](beta)-haemolytic Streptococci
This is further divided into Group A Streptococci (Streptococcus pyogenes) and Group B Streptococci (Streptococcus agalactiae)
Group A Streptococci is transmitted through coughs, sneezes, or direct contact. It can be non-invasive (i.e. does not spread inside the bloodstream) or invasive (which means it spreads to the bloodstream and other body sites).
Group B Streptococci in general lives harmlessly inside female genitals and digestive system. It is transmitted either through sexual contact or from the mother to a baby during birth. That is why Group B Streptococci mostly affects newborns as the bacteria get passed from mother to infant through the amniotic fluid.
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Streptococcus Pyogenes Morphology
They are gram-positive bacteria.
They have a diameter of five to one μm.
They are non-motile (can not move) and non-sporing (do not form spores).
They contain a protein called Protein F.
Some of the streptococcus strains are capsulated and can be seen best in young cultures.
They are fimbriated. It means they have a border or fringe of fingerlike or hairlike projections.
The walls of its cell contain group-specific carbohydrates.
Streptococcus Habitats
They are found in the skin and throat of humans.
They obtain their nutrients from the upper respiratory tract.
They are opportunistic pathogens which means they do not infect healthy hosts but cause infections in hospitals to immunosuppressed people.
They can survive in dust for a little while.
The carrier rate of this pathogen in adults is very few and around 10% in kids going to kindergarten.
Streptococcus Classifications
There are many ways that streptococcus bacteria can be classified. They can be segregated into different categories based on:
Oxygen requirement.
The hemolytic pattern on sheep blood agar (Brown classification).
Physiological characteristics (Shermann’s classification).
Serological classification (Lancefield’s classification).
Biochemical classification.
16 rRNA sequence.
We will look into the details of some of the classifications mentioned above.
Streptococcus Classification based on oxygen requirement:
Aerobic anaerobes such as Streptococcus spp
Obligate anaerobes such as Peptostreptococcus
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Brown Classification
Αlpha-Haemolysis Group - These show greenish discoloration and form incomplete hemolysis on blood agar.
Beta-Haemolysis Group - These form complete hemolysis on blood agar.
Non-Haemolysis Group - These do not cause hemolysis at all for example Streptococcus faecalis.
Sherman's Classification
Lactococci - They are a non-hemolytic group and are found in dairy products for example Lactococcus.
Enterococci - They are present as normal human intestinal flora for example Enterococcus.
Viridans Streptococci - They are present as normal human upper respiratory tract flora.
Streptococcal Skin Infection
You can get many skin diseases if you come in direct contact with streptococcus bacteria. Some of the common ones are:
Impetigo - A superficial bacterial infection that forms honey-colored crusted erosions (also called “school sores”).
Ecthyma - It forms crusted sores and ulcers get produced beneath these crusts. It is a more severe form of impetigo.
Cellulitis - This infection occurs in subcutaneous tissues and the lower dermis. It gives localized red, swollen, and painful skin. If not treated, cellulitis can turn life-threatening.
Erysipelas - It affects the upper dermis and is a superficial form of cellulitis that extends into superficial cutaneous lymphatics. Owing to the intense rash caused by this infection, it is also referred to as St.Anthony’s fire.
Necrotizing Fasciitis - It is an extremely serious bacterial infection that occurs in fascia and soft tissues. It causes thrombosis (blood clots) in blood vessels as this bacteria multiplies and releases toxic enzymes.
Tropical ulcers
Streptococcus is a bacterial infection caused by Streptococcus pyogenes and it affects the throat and skin region. This infection can range from mild to extremely severe and cause fatalities. Streptococcus is a highly contagious infection and usually spreads by the cough and sneeze of an infected person. Streptococcus is seen more in kindergarten-going kids than in adults.
FAQs on Streptococcus: Key Facts, Types & Clinical Relevance
1. What is Streptococcus and where is it commonly found?
Streptococcus is a genus of spherical, Gram-positive bacteria that typically grow in chains or pairs. These bacteria are ubiquitous in nature and are part of the normal human flora, commonly found in the throat, nose, skin, and intestines. While many species are harmless commensals, several are significant human pathogens responsible for a wide range of diseases.
2. How is a Streptococcus infection, like strep throat, transmitted?
Streptococcus infections, particularly those caused by Group A Streptococcus (like strep throat), are highly contagious. The primary modes of transmission include:
Respiratory Droplets: Inhaling small droplets released when an infected person coughs or sneezes.
Direct Contact: Touching contaminated surfaces and then touching your mouth, nose, or eyes.
Shared Items: Sharing utensils, cups, or food with an infected individual.
Skin Contact: Coming into contact with sores on the skin caused by Streptococcus, such as in impetigo.
3. What are the major diseases caused by different species of Streptococcus?
Different species and groups of Streptococcus cause a variety of diseases, ranging from mild to life-threatening. Key examples include:
Streptococcus pyogenes (Group A): Causes strep throat, scarlet fever, impetigo, and more severe conditions like necrotizing fasciitis and streptococcal toxic shock syndrome.
Streptococcus pneumoniae: A leading cause of bacterial pneumonia, meningitis, and otitis media (middle ear infections).
Streptococcus agalactiae (Group B): Can cause serious infections in newborns, such as sepsis and meningitis.
Viridans Streptococci: A group of species that are part of the oral flora but can cause dental caries and infective endocarditis.
4. What is the role of Streptococcus pneumoniae as per the CBSE syllabus?
As per the CBSE Class 12 Biology syllabus under 'Human Health and Diseases', Streptococcus pneumoniae is a key example of a pathogenic bacterium. It is cited as one of the primary causative agents of pneumonia. The infection leads to inflammation of the alveoli (air sacs) in the lungs, which then get filled with fluid, causing severe respiratory problems like fever, chills, cough, and difficulty breathing.
5. How are streptococcal infections typically diagnosed and treated?
Diagnosis of a streptococcal infection often involves a physical examination and laboratory tests. For strep throat, a rapid antigen detection test (rapid strep test) or a throat culture is performed. Treatment for bacterial infections caused by Streptococcus primarily involves a course of antibiotics, such as penicillin or amoxicillin, to eliminate the bacteria, relieve symptoms, and prevent complications.
6. Why is Streptococcus classified as a Gram-positive bacterium?
Streptococcus is classified as Gram-positive because of the structure of its cell wall. During the Gram staining procedure, its thick peptidoglycan layer retains the primary crystal violet stain, causing the bacteria to appear purple under a microscope. This is in contrast to Gram-negative bacteria, which have a thin peptidoglycan layer and an outer membrane, causing them to lose the primary stain and take up the red counterstain.
7. How are Streptococcus bacteria classified into different groups like Group A and Group B?
Streptococcus bacteria are often classified using the Lancefield grouping system. This system categorises them based on the specific carbohydrate antigens present on their cell walls. For example, Streptococcus pyogenes has the Group A antigen, while Streptococcus agalactiae has the Group B antigen. This classification is medically important as it helps in identifying the species and predicting the types of diseases they might cause.
8. What is the main difference between Streptococcus and Staphylococcus bacteria?
The main difference between Streptococcus and Staphylococcus lies in their microscopic appearance and arrangement. Both are Gram-positive cocci, but:
Streptococcus grows in chains or pairs because the cells divide along a single axis.
Staphylococcus grows in grape-like clusters because the cells divide along multiple axes.
This simple morphological difference is a key initial step in their laboratory identification.
9. Why can some Streptococcus infections lead to serious complications like rheumatic fever?
Certain Streptococcus infections, specifically those caused by Group A Streptococcus, can trigger post-infectious complications like rheumatic fever. This is not a direct infection but an autoimmune response. The immune system, in its attempt to fight the strep bacteria, produces antibodies that can cross-react with the body's own tissues, particularly in the heart, joints, skin, and brain. This happens because some proteins on the streptococcal surface mimic proteins in human tissues, leading to an autoimmune attack.
