Friday, August 27, 2010

Streptococcus pyogenes-a Gram-positive

Streptococcus pyogenes (group A streptococcus) is a Gram-positive, immobile, nonsporeforming coccus occurring in the network or in pairs of cells. Individual cells are round to ovoid cocci, 0.6 to 1.0 microns in diameter (Fig. 1). Distribution of streptococci in a plane, and therefore occur in pairs, or (particularly in tests of fluid or material) in the network of variable length. The metabolism of S. pyogenes is fermentative, catalase-negative anaerobic organism aérotolérantes anaerobic (facultative anaerobes) and requires enriched medium containing blood to grow. Streptococcus group typically consists of a capsule of hyaluronic acid and beta show hemolysis (clear) on blood agar.



Group A streptococci are human parasites and Streptococcus pyogenes is a human pathogen most frequently. It is estimated that between 5-15% of normal individuals harbor Streptococcus pyogenes, mainly in the respiratory tract, without signs of disease. During the host defense is compromised, or when the body is able to exert its virulence, or when it is placed on the sensitive tissues or hosts, acute infection.

During the last century, infections by S. pyogenes claimed many lives especially since the body is the most important cause of puerperal fever (sepsis after childbirth). Scarlet fever once a serious complication of streptococcal infection, but now, thanks to antibiotic treatment, it is a little more strep throat accompanied by a rash. Similarly, Rose (a type of cellulitis accompanied by fever and systemic toxicity) is less common today. However, there has been a recent increase in the variety, severity and consequences of infection with Streptococcus pyogenes and the resurgence of severe invasive infections, prompting descriptions of skin bacteria "eat" in the media. A full explanation of inheritance and rebirth is not known. Today, the pathogen of major concern because of sporadic cases of rapidly progressive disease and because of the low risk of serious consequences of untreated infections in. These diseases are a major health problem worldwide, and effort is directed to clarify the risks and consequences and the identification of strains and rheumatogenic nephritogenic streptococci.

Acute Streptococcus pyogenes infections may present as pharyngitis (sore throat), scarlet fever (rash), impetigo (infection of the superficial layers of the skin) or cellulitis (infection of the deeper layers of the skin). Invasive, toxic, can cause infection of necrotizing fasciitis, myositis and streptococcal toxic shock syndrome. Patients may also develop the immune system after streptococcal sequelae such as rheumatic fever and acute glomerulonephritis, following acute infections caused by Streptococcus pyogenes.

Streptococcus pyogenes produces a wide range of virulence factors and a wide range of diseases. virulence factors of group A streptococci include: (1) M-protein associated with cellular protein (protein F) and lipoteichoic acid to observe, (2) hyaluronic acid capsule immunological disguise and inhibits phagocytosis, M protein inhibits phagocytosis (3) invasins such as streptokinase, streptodornase (DNase B), hyaluronidase and streptolysin, (4) exotoxins, such as auto-ignition (erythrogenic) toxin which causes a rash of scarlet fever and systemic syndrome toxic shock.

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