Streptococcus

• It is gram positive, spherical bacteria that from pairs or long chains
• Widely distributed in nature
• Streptococcus pyogenes cause necrotizing fasciitis
• Bacteria that cause necrotizing fasciitis is termed flash eating bacteria
• Streptococcus pyogenes is group A
• Streptococcus pyogenes is β-haemolysis
• Streptococcus pneumoniae is from none group
• Streptococcus pneumoniae is ∝-haemolysis
• Peptostreptococcus are from none group and none , ∝ - haemolysis
• Enterococcus faecalis is from group D and non or ∝ - haemolysis
• Streptococcus pyogenes is PYR - positive
• Most streptococci grow best at 37 °C
• Growth and haemolysis are aided by 10% of CO2
• Most streptococci are facultative anaerobes and grow under both aerobic and anaerobic
• Streptococcus pyogenes grow on blood agar
• M protein is major virulence factor of streptococcus pyogenes
• M protein is able to resist phagocytosis by leukocytes
• Immunity to infection is related to type specific antibodies to M protein
• Class I M protein cause Rheumatic fever
• T substance has no relationship to virulence
• Neucleoproteins called P protein make up most of the streptococcal cell body
• Streptococcus pyogenes produce more than 20 extracellular toxins and enzymes
• Streptokinase ( fibrinolysin) allow the bacteria to escape from blood clot
• Streptococcal deoxyribonuclease facilitate spread of streptococci by liquefying pus
• Hyaluronidase splits hyaluronic acid, an important component of the ground substance of connective tissue
• Hyaluronidase is spreading factor
• Pyrogenic exotoxins ( erythrogenic toxin )

  • There are streptococcal pyrogenic exotoxins ( Spe ) : A , B and C
• Spe is associated with streptococcal toxic shock syndrome and scarlet fever
• Streptococcus pyogenes produce two haemolysins. ( streptolysins O and streptolysins S )
• Antistreptolysin O ( ASO ) appears in human after infection with streptococcus
• ASO blocks haemolysis by SO
• ASO serum In excess of 160-200 units is considered abnormally high and suggest either recent infection or a hypersensitive person
• Streptolysins S isn't antigenic and inhibited by a non-specific inhibitor
• Necrotizing fasciitis is termed streptococcal gangrene
• Bacteria other than streptococcus pyogenes can also cause necrotizing fasciitis
• Erysipelas and cellulitis can happen
• Bacteremia or sepsis and puerperal fever can occur
• Puerperal fever is a septicemia originating
• Most common infection is sore throat or pharyngitis
• M types 49, 57, 59-61 cause glomerulonephritis but not Rheumatic fever