Overview Of Streptococcus Pyogenes, Its Epidemioligy And Clinical Significance

According to Fimbres, A. M. , and Shulman, S. T. (2007) group A streptococcus (GAS) causes a widest range of syndromes of any bacterium, including simple skin infections and pharyngitis, bacteremia, necrotizing fasciitis, the toxin-mediated streptococcal toxic shock syndrome (STSS), and immune-mediated illnesses such as acute rheumatic fever and acute glomerulonephritis. Streptococcus pyogenes or otherwise known as GAS, are facultative anaerobic Gram-positive cocci that typically form chains. Its optimal growth occurs at pH 7. 4-7. 6 in a nutritionally complex medium containing defibrinated blood or serum at 37◦C and a reduced oxygen and carbon dioxide-enriched environment. The characteristic colonies is clear, complete hemolysis on 5% sheep blood agar. The structure is composed of hyaluronate capsule, fimbriae, a complex cell wall, and a sytoplasmic membrane enclosing the cytoplasm. Dr. Rebecca Lancefield developed the serologic classification of β streptococci that is based on the antigenicity of the cell wall polysaccharides, and for Streptococcus pyogenes this is the A polysaccharide.

In rapid antigen detection test where extraction of the group-specific carbohydrate antigen from the GAS cell wall to identify the antigen by immunological reaction. Streptococcus pyogenes has its virulence factor that protects them from phagocytosis, and one of its major surface protein virulent is the protein M that protrudes at the surface of its cell wall. Some of the strains of Streptococcus pyogenes contains serum opacity factor (SOF) on their surface, to identify this strain serologically it shares serologic specificity a lipoproteinase with M types. A very large variety of biologically active extracellular substances that Streptococcus pyogenes secreted, including streptolysin O, an immunogenic hemolysin, and DNAse B, an immunogenic DNAse. Epidemiology The Streptococcus pyogenes are prone to those who are living in crowded conditions such as military barracks, college dormitories and large families and can be easily acquired through respiratory droplets from person to person contact. In some rare case that pharyngitis-causing Streptococcus pyogenes is transmitted in fomites or in contaminated dust. School-aged children peaking at approximately 8 years are commonly prone to acquire streptococcal pharyngitis (Fimbres, A. M. , and Shulman, S. T. 2007).

Clinical Significance Streptococcal Toxic Shock Syndrome was reported to be associated with GAS bacteremia causing syndrome of toxic shock and multi-organ system failure. This associated with an increased prevalence of certain M-protein serotypes, M1 and M3, and an increase in number of strain producing streptococcal pyrogenic exotoxin A. The clinical criteria are hypotension, multi-organ system involvement including hepatic, renal, gastrointestinal, pulmonary and hematologic systems, and generalized skin infections, specifically an erythematous rash and desquamation. Among children, varicella infection (chicken pox) is consider to one major risk factor for invasive GAS infections and STSS. But with the help of the introduction of universal varicella vaccination in USA, it reduced the rate of varicella-related invasive GAS infections.

According by Patel et al that is stated in the study of Frimbres et al, over a span of 9 years, the rate of varicella-related invasive GAS infections as a percentage of all invasive GAS infections in children has declined from 27% in the prevaccine era (1993-1995) to 2% after widespread vaccine use (1999-2001). Necrotizing fasciitis The most severe form of soft tissue infection primarily involving the superficial fascia is called necrotizing fasciitis. This disease causing liquefactive necrosis where it spread and proliferate in superficial fascia. As the process worsen, sealing of nutrient to the skin causes progressive skin ischemia and gangrene that ultimately leads to death of the subcutaneous fat, dermis and epidermis. The appearance of the subcutaneous tissues is the most important diagnostic feature of necrotizing fasciitis at the time of surgical examination.

The fascia tend to appear as swollen and dull gray appearance with stringy areas of necrosis. The exudates from the wound denote a thin, brownish exudate termed ‘dishwasher pus’. The specimen is easily acquired with the use of blunt instrument then bacteriological diagnosis is established by positive blood culture results or by culturing the acquired tissue specimens taken in the operating room. Necrotizing fasciitis is usually accompanied by streptococcal toxic shock syndrome if it caused by Streptococcus pyogenes. It is treated with clindamycin and penicillin, if streptococcal toxic shock syndrome is suspected. Clindamycin is effective because it demonstrate both toxin suppression and modulation of cytokine production and probably is more effective against invasive GAS infections. The treatment for necrotizing fasciitis that is particularly known to be caused by GAS or to be associated with a toxic shock syndrome is the vaccinia immune globulin, and known to possess neutralizing antibodies to streptococcal toxins and superatigens.