BY: SHAILY SHARMA (MSIWM041)
Streptococcus pyogenes (which is also called group A streptococcus) is by far one of the most harmful and serious streptococcal pathogens of humans. It is a strict pathogen that inhabits the throat, nasopharynx and occasionally even the skin in humans.
Dissemination of the bacteria to other sites within the body causes a variety of severely invasive conditions which have an association with high morbidity and mortality.
When these streptococci are grown on blood agar, typically, small zones of beta-hemolysis of 2-3mm are seen.
Streptococcus pyogenes also demonstrate the ability of biofilm formation to communicate with other neighboring cells like other bacterial cells. The gene for biofilm formation controlled via quorum sensing.
Characteristics of the pathogen are:
- Microscopic Morphology:
- It is a gram-positive coccus which is arranged in chains and pairs.
- It is not usually motile and the occurrence of motility is considered rare.
- It is non-spore-forming.
- A catalase test is used to distinguish the Streptococcus (negative) from the Staphylococcus (positive).
- The hallmarks of S. pyogenes include beta-hemolysis and sensitivity to bacitracin (antimicrobial agent).
- A rapid way for identification is to use monoclonal antibodies that detect the C-carbohydrate found on the surface of the cell of S. pyogenes.
- S. pyogenes is a fairly strict parasite which is found mainly in the throat, nasopharynx and occasionally in the skin of humans.
- Most people (approximately 5% to 15%) are asymptomatic carries.
- Virulence factors:
- The cell surface antigens present on S. pyogenes provide the virulence factors to the pathogen.
- Some examples of such surface antigens are:
- C-carbohydrate: It prevents the bacterium from getting dissolved in the lysozyme, which may be present in the throat and the nasopharynx, of the host.
- Fimbriae: These are present on the outer surface of the cell. They are responsible for enhancing the adherence of the bacterium to the host cell.
- M-protein: This protein helps in the resistance to phagocytosis and also improves the adherence of the pathogen to the host cells.
- C5a protease: It is an enzyme that catalyzes the cleavage of the C5a protein of the complement system which prevents the hosts immune system from attacking the pathogen by disrupting the formation of the membrane attack complex (MAC).
- Some strains of the bacterium have hyaluronic acid (HA) present on the surface which is identical to the HA found in host cells, this HA prevents the immune response by the host.
- Streptolysin O (SLO) and Streptolysin S (SLS): They are two different type of hemolysins which damage the hosts leukocytes, heart and liver muscles.
- Streptokinase, hyaluronidase, streptodornase: These are enzymes which aid in the invasion of the hosts body by digesting fibrin clots, connective tissues and DNA respectively.
- Primary infections/Disease:
- It causes local cutaneous infections like impetigo (pyoderma) or erysipelas which is more invasive.
- Streptococcal pharyngitis is caused by the infection of the tonsils and the pharyngeal mucous membranes (strep throat) which can lead to scarlet fever if left untreated.
- The long-term complications of S. pyogenes are rheumatic fever and acute glomerulonephritis.
- Control and treatment:
- S. pyogenes can be controlled by limiting the contact between carries of the bacterium and immunocompromised hosts.
- Isolation of patients must be done and care should be taken while handling the infectious secretions.
- The treatment is usually a simple course of penicillin since the bacterium shows little drug resistance.
S. pyogenes do have some applications in the field of bionanotechnology and genome editing as well.
– In bionanotechnology; the proteins of S. pyogenes have some unique properties which are harnessed to produce a route to enhance the effectiveness of antibody therapy.
– In genome editing; The CRISPR system of S. pyogenes is used to recognize and destroy DNA from invading viruses, thereby stopping the infection.
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Deltcheva E, Chylinski K, Sharma CM, Gonzales K, Chao Y, Pirzada ZA, Eckert MR, Vogel J, Charpentier E (March 2011). “CRISPR RNA maturation by trans-encoded small RNA and host factor RNase III”. Nature. 471 (7340): 602–607. Bibcode:2011Natur.471..602D. doi:10.1038/nature09886. PMC 3070239. PMID 21455174.
Foundations in Microbiology (ninth edition) by Kathleen Park Talaro, Barry Chess