Streptococcus Pyogenes Overview
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Published: Tue, 12 Sep 2017
The beta-hemolytic bacterium Streptococcus pyogenes formally belongs to the family Streptococcaceae, where it is known to be the most pathogenic bacterium out of its entire genus because of the wide spectrum of diseases it is known to cause. However, Streptococcus pyogenes is a ubiquitous, facultative anaerobic bacterium that can be located in the nasal passageways of some healthy individuals due to its ideal environment for microbes. It is a gram positive bacteria that is classified as a group A Streptococci (GAS) that is unique in its ability to cause a wide range of different onsets of illness in its host such as tonsillitis, scarlet fever, cellulitis, erysipelas post-streptococcal glomerulonephritis, necrotizing fasciitis, myonecrosis and lymphangitis. The name Streptococcus is a derivative from the Greek word ‘Streptos’ meaning easily twisted or to bend and likewise to pyogenes which is a derivative from the word pyogenic, which is a classification for Streptococci that are compatible with pus formation.
Humans are the common reservoir for Streptococcus pyogenes which is capable of causing an array of different symptoms depending on the direct illness it is inflicting on its host. However, it is commonly known for being the culprit behind Streptococcal pharyngitis (Strep throat), where it can cause a mild to severe sore throat accompanied with a fever, tender/swollen lymph nodes and irritated tonsils. It is highly successful in its fast commute from one person to the next. The transmission can be as simple and innocent as the swap of nasal or throat secretions via airborne droplets or from sharing contaminated food and drinks. Strep throat shows no discrimination in the ages it infects. Although, it tends to be more prevalent in young children. Even though Strep throat is highly contagious it is typically a short lived illness that is easily treated by health care providers with the proper course of anti-biotics. If left untreated or mistreated complications such as rheumatic fever can arise, which is the body’s over driven immune response to the infection. On the other end of the spectrum Streptococcus pyogenes can cause a more detrimental onset of symptoms with the disease known as Necrotizing Fasciitis (The flesh eating disease). Necrotizing Fasciitis is a rare inflammatory infection that promptly targets the fascia and subcutaneous tissues leaving painful blisters and redness on the surface of the infected areas of skin. The symptoms commonly associated with this disease range from flu-like symptoms, the presence of boil-like blisters, discoloration, infrequent urination and significant swelling of the infected area. It is generally spread through direct contact with open or infected wounds on individuals. Unlike Strep throat, Necrotizing Fasciitis is not as commonly seen or as easily treated. It has a high mortality rate, with 1 out of 4 infected people dying from it. ( SITE). However, healthy individuals who practice proper daily hygiene typically don’t have to worry about becoming infected with Necrotizing Fasciitis. People who are at a greater risk include those who have had recent surgery, a compromised immune system , abrasions on the skin, diabetes, cancer, have had previous surgery etc. Streptococcus pyogenes is a non-sporing bacterium that is non-motile in nature and can be observed in chains and clumps of cocci that are less than 2 µm in length, producing impressive sized colonies greater than 0.5 mm. There are several different unique M serotypes that contribute to the different diseases caused by Streptococcus pyogenes. Some of strains of M serotypes include Streptolysin O, Streptolysin S, Streptodornase, Streptococcal chemokine protease, Hyaluronidase, Streptokinase, etc. Streptolysin O is a toxin that works on the cell membranes permeability in order to allow for more adequate uptake of larger charged molecules. Streptolysis S……
Clinical Significance. Streptococcus Pyogenes is self- equipped with many virulence factors that are highly advantageous in its evasion of the host’s immune response in order to make it every bit of possible to establish a productive infection within its host. Initially lipoteichoic aid (LTA) allow for the bacteria to establish an adhering relationship between the cellular surface or mucosa of epithelial cells.(depending on the area of attachment). Protein F (Fibronectin binding protein) comes in and acts as a strong binding reinforcer between the bacteria and its surface of chosen attachment. However, all the while if the bacterium entered through the mouth it may be encountered with secretory IgA antibody in the saliva trying to counter the effects of the antigens on its surfaces to loosen the bacterium. The successful bacterium than quickly begin replicating and colonizing the appealing greater surface area on the tonsils, causing swollen lymph glands and tissue damage as the bacterium produces compounds like Hyaluronidase to degrade the mammalian cells. The secretions of bradykinins and chemokines result due to the host’s tissue damage which initiate the process of inflammation. The increase of inflammation as well as the rapid ongoing bacterium replication results in the sequence of many immune cells, specifically being neutrophils, macrophages, T-cells, B-cells and dendritic cells. The swollen glands are a direct result of the T -cells increasingly occupying the tonsils while the appearance of yellow pus in the back of the throat is result of the demise of neutrophils. The M protein along with an outer hyaluronic acid capsule aid the bacteria in resisting phagocytosis. All the while pyogenes has established mechanisms to counter specific responses of the host immune response such as T-cell proliferation, counter against neutrophil extracellular traps (NETs), degradation of IgG,etc.
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