Normal flora of upper respiratory tract.

The mucous membrane of the mouth and pharnyx are usually sterile at birth,but during birth labor at passage through birth canal,within 4-12 hours after birth,viridans steptococci is establised as prominent member of the normal flora and remain for life.Originates from respiratory tract of the mother or attendants.early in life aerobic and anaerobic staphylococci ,gram neagtive diplococci(nesisseriae ,moraxella catarrhalis )diphtheroids,and occational lactobalccili are added.Actinomyces species are also normally present in tonsillar tissue .Predominant in respiratory tract ,especially at pharnyx ,are non hemolytic and alpha hemolytic streptocci and neisseriae.Staphylococci ,diphtheroids ,hemophilli ,pneumococci,mycoplasma ,prevotelle are encountered.

Streptococcus pyrogens-group a streptococcus.Indiviual cocci are sherical or oviod and arranged in chains,members of the chain ,have a striing diplococcal apperance,sometimes rod like.They are gram positive,but sometimes lose their positivity,when bacteria dies.Cell wall,contains(M,R,T antigens),carbohyrates(group specific)nd peptidoglycans.Hair like pilli projects through the capsule of group A streptococci.Pilli are covered with lipoteichoic acid.

Cultures They grow in solid media ,usually 1-2 diameters.S.pyrogenes are beta hemolytic

Antigenic structureMajor virulence factor(M protein),it appears as hair like structures on the cell wall.When absent is not virulent.

Toxins and enzymesStreptokinase(fibrinolysin)Transforms plasminogen into plasmin,which digest fibrin.

Hyaluronidase It spits hyaluronic acid,an important component of ground substance,therefore hyaluronidase helps the spread of the infection.

Pyrogenic exotoxins3 exotoxins,a,b,c.exotoxin a has been mostly studied ,and has been associated with streptococcal toxic syndrome and scarlet fever.

Diphosphopyridine nucleotidase Related to organisms ability to kill leukocytes.

Hemolysin(streptolysin)Streptoloysin o,with this antistreptolysin o is formed and is and antibody which appears in human following infection with strptococci.

Pathogenesis(based on invasion)A)erysipelas-if portal of entry is the skin,erysipelas results,with edema.B)CellulitisC)Necrotizing fascilitis-flesh eating bacteriaD)Puerperal fever-E)Bacterimia-

Local infection and their productStreptococcal sore throat-they adhere to the pharygeal epithelium by lipoteichoic acid and hyaluronic acid.In infants and small children,is subacute with thin serous dischare and a little fever,the infection could spread to the ear and mastoid.cervical nodes are enlarged.in older children,the disease is more acute,and is characterized by intense nasopharygitis ,tonsillitis ,and intense redness and edema,with purulent exudate,tender cervical nodes,it dose not usually invole the lungs.

Streptococcal pyodermaLocal infections of the superfical layers of the skin(impetigo),

Invasive group a infections ,streptococcal toxic shock syndrome,and scarlet feverSchock charcterized by bacteremia,respiratory failure,multiorgan failure.For scarlet fever pyrogenic a and c can cause pharygitis or skin and soft tissue infection

Poststreptococcal diseases(Rheumatic fever,glomerulonephritis)After acute infection,there is a 1-4 weeks latent period after which nephritis or rheumatic fever occasionally develops.Nephritis is more commonly preceded by infections of the skin,where as rheumatic fever is preceded from respiratory tract.