Introduction
Strepto pyogenes was first introduced and narrated by Billroth on the verge of third and fourth quarters of the nineteenth century (1874). This first description came when the microorganism was detected from the infected wounds. Further work by Fehleisen resulted in isolation of organisms on cultures from perierysipelas lesions within the next decade; these organisms settled them in chains on the culture media. So, after a year Rosenbach called them for the first time as S pyogenes.
Main text
S pyogenes belong to the phylum firmicutes, class bacilli, genus streptococcus, order lactobacillus, family streptococcaceae and species s pyogenes. It is a spherical gram positive bacterium and when cultured, it grows on media in long chains. Group A streptococcal infections are caused by this microorganism. It produces group A antigen on its cell wall; it also displays beta-hemolysis when the culture medium used is blood agar. One of its unique features is large zones of hemolysis because of the complete disruption of red blood corpuscles and as a result release of hemoglobin. This microorganism is catalase-negative with an incubation period of ten days when the conditions are favorable.
Initially, different types of hemolyses were described by Brown which was followed by the Lancefield classification of beta-hemolytic streptococci by serotyping on the basis of M-protein precipitin reactions. It was at this time that the role of M protein was established in disease causation.
Different scientists including George and Dick determined that scarlet fever was the result of this microorganism.
The other two very important autoimmune diseases, acute rheumatic fever and glomerulonephritis, have also been linked to post-infectious sequelae of hemolytic streptococcal infections.
Metabolism
Like metabolic needs and their satisfaction in other microorganisms, S.pyogenes has also got various pathways and chemical reactions that maintain the metabolic needs of the microorganism. Some of these pathways or chemical reactions are given below:
Heterotrophic Metabolism
It is the biologic oxidation of organic compounds, as glucose, to produce ATP and inorganic compound. This energy-producing step is required by the microorganism to meet its demand.
Respiration
It is a type of heterotrophic metabolism in which oxidation of glucose takes place. The process results in the production of 38 moles of ATPs from 1 mole of glucose, thus yielding approximately 380,000 cal.
Fermentation
This is a process in which comparatively less amount of energy is produced. Here some organic compound replaces oxygen, in comparison to respiration; therefore, this process supports the anaerobic respiration.
Krebs Cycle
Although, this is an oxidative reaction, pyruvate instead of glucose, is the substrate to be oxidized. In this cycle 15 moles of ATP are produced.
Electron Transport and Oxidative Phosphorylation
There is a series of electron transfer reactions that takes place at the terminal stages of the respiration and eventually ATP is produced. The process occurs in the cytoplasmic membrane where the process of phosphorylation of ADP to ATP produces energy. Various types of cytochrome, flavins and cytochrome oxidases are utilized.
Bacterial Photosynthesis
It is an anaerobic mode of metabolism which needs light.
Carbon dioxide reduced to glucose which is the substrate to be used for energy production. Two types of processes, photolithotrophic and photoorganotrophic, exist in these microorganisms like others.
Autotrophy
This mode of metabolism is also known as, chemotrophic and chemoautotrophy. This is a unique type of metabolism that takes place only in bacteria. In this type, inorganic compounds are oxidized directly, excluding sunlight, to yield energy (e.g., NH3, NO2–, S2, and Fe2+).
Anaerobic Respiration
This process is similar to the respiration wherein the terminal stages oxygen acts as electron acceptors; here instead of oxygen some other compounds are utilized for this purpose, including NO3–, SO42–, fumarate, and even CO2 for methane-producing bacteria.
The Nitrogen Cycle
This cycle is actually a recycling mechanism where organic and inorganic nitrogen compounds are metabolic. This way these compounds are recycled among bacteria, plants and animals. Actually, this important type has got very important role in maintaining the nitrogen balance in the nature.
Virulence factors
S. pyogenes contains a variety of factors which help it in invading the host cells and provide facilitation in this regard.
Capsule
A carbohydrate capsule is the outermost layer which surrounds the microorganism; it is composed of hyaluronic acid. This acts as a protective layer especially providing protection from phagocytosis.
Cell Wall Proteins, M and F
Moreover, this capsule and some other factors embedded in the cell wall along with the capsule favor attachment of S. pyogenes to the host cells. These factors are M protein which is composed of lipoteichoic acid and protein F (SfbI).
M protein inhibits opsonization when it binds to host complement regulators when the alternative complement pathway is active. Being part of some serotypes, M protein also prevents opsonization by binding to fibrinogen.
Releasing Factors
In addition to the components of the microorganism which helps in the process of the invasion, some chemicals are released from S.pyogenes and contain the qualities of a virulence factor.
Some of these chemicals are described here:
Streptolysin O and S
This microorganism releases some toxins, the substances which are lethal to the host cells. Based on these toxins S. pyogenes produces beta-hemolysis. Moreover, Streptolysin O has got poisonous characteristics to those host cells which are an important component of the defence system, neutrophils and other cells. The individuals who are infected by this microorganism they react by producing antibodies as a result of an immune response. These antibodies when detected in the serum of the infected individuals help in the diagnosis of infection.
Streptolysin O has also got cardiotoxicity.
Streptococcal pyrogenic exotoxins A and C
Spe are the streptococcal pyrogenic exotoxins, SpeA and SpeC. These are secreted by a lot of strains of this microorganism and termed as the superantigens. The rash and scarlet fever are the examples of infections initiated by these exotoxins along with some of the symptoms of toxic shock syndrome.
Streptokinase
It is an enzyme which activates another proteolytic enzyme, plasminogen.
After activation this enzyme digests some proteins including fibrin which helps in waling off the infection.
Hyaluronidase
Hyaluronic acid is one of the basic components of the connective tissue and provides structure to this tissue. As the name exhibits, the above-mentioned enzyme results in the breaking down process of this connective tissue component. As this structure disrupts the spread of infection becomes easier.
But there is some paradox! There is a small number of isolates that have got the ability to produce active hyaluronidase; also the strains that have got this ability do not the spread through skin or connective tissue.
Streptodornase
DNases are the enzymes which act as the defence system as they protect bacteria from getting trapped in the webs produced by DNA.
C5apeptidase
The complement system produces C5a, a neutrophil chemotaxis. It attracts the neutrophils when an external insult especially in the form of a microorganism. This peptidase enzymatically dissolves this chemotaxis and disrupts the communication mechanism between the complement system and neutrophils.
Streptococcal chemokine protease
Severe cases of necrotizing fasciitis are deficient in neutrophils. S.pyogenes releases ScpC, a serine protease, which interrupts the movement and migration of the neutrophils towards the infection site. This takes place when chemokine IL-8 is dissolved by ScpC.
Chemokine IL-8 actually attracts neutrophils to the infected site.
Factors which make S.pyogenes vulnerable
M protein which is involved in the inhibition of opsonisation, is also the component of this microorganism which places at a greater risk. In fat, it is the characteristic that weakens S. pyogenes. The point is that whenever immune response develops against this microorganism the host produces antibodies that are targeted to the microorganism through this M protein. As this protein is unique for each strain so the response is also unique.
Control
Penicillin is the treatment of choice. It requires starting treatment at an appropriate time. If time is taken care off then the chances of developing glomerulonephritis and rheumatic fever become very low. There is no vaccine developed yet but the efforts are on the way.
Public Health
S.pyogenes produces usually airborne infections but fomites may also get involved. The high time for the respiratory and skin infection is the childhood. There are asymptomatic carriers that can also transmit infection. Acute rheumatic fever, although, in majority of the cases is developed in poor but it also has got some association through genetics.
Being the normal flora it can cause infection of the site where it resides; may result in neonatal infection as normally it is present in the vagina.