streptococcus IMPORTANT PROPERTIES 1-streptococci are spherical gram-positive cocci. 2-arranged in chain or pairs. 3-all streptococci are catalase negative. 4-one of the most important characteristic for identification of streptococci is the type of hemolysis :

alpha-hemolytic streptococci form a green zone around their colonies as result of incomplete lysis of red blood cells in the agar. beta-hemolytic streptococci form a clear zone around their colonies because complete lysis of the red cell occurs. Beta-hemolysis is due to the production of enzymes (hemolysin) called streptolysin O and streptolysin S. some streptococci are nonhemolytic (gama-hemolysis) 5-there are tow important antigens of beta-hemolytic streptococci: a-C carbohydrate determine the group pf beta hemolytic streptococci.it is local in the cell wall and it is specificity is determined by an amino sugar b- M protein is the most important virulence factor and determine the type of group A beta-hemolytic streptococci.

Classification of streptococci First: beta-hemolytic streptococci these are arranged into groups on the basis of antigenic differences in C carbohydrate 1-group A streptococci (streptococcus pyogens )are one of the most important human pathogens. They are the most frequent bacterial cause of pharyngitis and a very common cause at skin infection. 2-group B streptococci (str. Agalactiae )colonize the genital tract of some women and can cause neonate of meningitis and sepsis.

Second:Non-beta-hemolytic streptococci The principle alpha-hemolytic organisms are str. Pneumonia and the varidans group of streptococci (example str.mitis ) Third: some streptococci are nonhemolytic (gama- hemolysis)

Transmition Streptococci are part of the normal flora of the human throat,skin, and intestines but produce disease when they gain access to tissues or blood. Viridans streptococci and str. Pneumonia are found chiefly in the oropharynx; str. Pyogenes is found on the skin and in vagina and colon.

STREPTOCOCCI PYOGEN Pathogenesis: 1)Pharyngitis. 2)Skin infection (impetigo) 3)Nacrotizing fasciitis. 4)Toxic shock syndrome. 5)Tonsillitis. 6)Glomerulonephritis.

VIRULENCE FACTOR S. pyogenes has several virulence factors that enable it to attach to host tissues, evade the immune response, and spread by penetrating host tissue layers:virulence 1) A carbohydrate-based bacterial capsule composed of hyaluronic acid surrounds the bacterium, protecting it from phagocytosis by neutrophils.bacterial capsulehyaluronic acidphagocytosisneutrophils 2)several factors embedded in the cell wall, including M protein, lipoteichoic acid, and protein F (SfbI) facilitate attachment to various host cells. [10] M protein also inhibits opsonization by the alternative complement pathway by binding to host complement regulators.M proteinlipoteichoic acid [10]opsonizationcomplement pathway 3)exotoxine include : streptolysin O,streptolysin S,streptococcal pyrogenic exotoxin A (SpeA),streptococcal pyrogenic exotoxine C (speC).

Usually, a throat swab is taken to the laboratory for testing. A Gram stain is performed to show Gram-positive cocci in chains. Then, the organism is cultured on blood agar with an added bacitracin antibiotic disk to show beta- hemolytic colonies and sensitivity (zone of inhibition around the disk) for the antibiotic. Culture on agar not containing blood, and then performing the catalase test should show a negative reaction for all streptococci. S. pyogenes is CAMP and hippurate tests negative. Serological identification of the organism involves testing for the presence of group-A-specific polysaccharide in the bacterium's cell wall using the Phadebact test.Gram stainblood agarbacitracinbeta- hemolyticcatalaseCAMPhippuratePhadebact test Diagnosis