Streptococcus pyogenes: Characteristics, Classification, Antigenic structure, Toxins & Enzymes
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- เผยแพร่เมื่อ 24 ธ.ค. 2024
- #DRMAKKY #microbiology #microbiologystudent #microbiologylife #immunesystem #lifescienceskills
This video explains Streptococcus pyogenes Characteristics, Classification, Antigenic structure, Toxins & Enzymes. These bacteria are facultative anaerobic, G+ve coccus, non-motile, non-spore-forming, catalase (-ve) which grows in chains and causes infections in humans including pharyngitis, tonsillitis, scarlet fever, cellulitis, rheumatic fever, myonecrosis and lymphangitis. The only known reservoirs for Group A Streptococcus (GAS) in nature are the skin and mucous membranes of the human host. The cell wall of S. pyogenes consists of the following components: Capsular hyaluronic acid: Non-antigenic and has weak anti-phagocytic activity but protect streptococci against immunological attacks. Cell-wall: 1. Outer layer: Protein and lipoteichoic acid. 2. Middle layer: Group specific carbohydrates. 3. Inner layer: Peptidoglycan (mucoprotein), responsible for cell wall rigidity, and enhances non-specific resistance (pyogenic and thrombolytic activity). Group A-specific carbohydrates antigens (C-Ags): Serological (Lancefield) grouping of streptococci is done and divided into several groups (A to V). All streptococci except viridans (α-hemolytic) group has a carbohydrate layer.
Proteins: present in outer layer, produce surface protein antigens (F, M, T, and R), and useful in serological typing of S. pyogenes. F-protein: recognizes host fibronectin (a protein present in eukaryotic cells), and helps in attachment lipoteichoic acid and M-protein together. M-protein: Antigenic, acts as a virulence factor by inhibiting phagocytosis, heat, and acid-stable but susceptible to tryptic digestion, and covered with lipoteichoic acid that enables the organism to attach to epithelial cells. T-protein: common to many M-types, strongly antigenic, not associated with virulence, and not protective Ag. R-protein: strongly antigenic, non-type specific, and associated with some M-protein types called M-associated protein (MAP), not associated with virulence and not protective Ag. Pili (Fimbriae): Hair-like and project from the capsule, consists of partly M-protein, covered with lipoteichoic acid, important in the attachment of streptococci to epithelial cells.
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