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Streptococcal Diseases. Streptococcus pyogenes. Streptococcus pyogenes Pyogenes means pus producing. One of the most important pathogens Gram positive cocci in chains Lancefield Serological Group A Beta Hemolytic on blood agar. Gram Stain of S. pyogenes. Hemolysis on Blood Agar Plates.

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Streptococcal Diseases

Streptococcus pyogenes


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Streptococcus pyogenesPyogenes means pus producing

  • One of the most important pathogens

  • Gram positive cocci in chains

  • Lancefield Serological Group A

  • Beta Hemolytic on blood agar


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Gram Stain of S. pyogenes


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Hemolysis on Blood Agar Plates

  • Alpha hemolysis-organism excretes hemolysins which partially break down rbc (incomplete hemolysis) thus a greenish zone appears around colony. S. pneumoniae

  • Beta hemolysis-organisms excretes potent hemoysins which completely lyse rbc (complete hemolysis) thus a clear zone appears around colony. S. pyogenes


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S.pyogenes

S. pneumonia

Beta hemolysis

Alpha hemolysis


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Diseases caused by S. pyogenes

  • Strep throat

  • Impetigo

  • Erysipelas

  • Cellulitis

  • Invasive Strep A infections

    • Necrotizing fasciitis

    • Myositis

    • Toxic shock-like syndrome


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Erysipelas

  • Acute infection and imflammation of the dermal layer of skin.

  • Painful red patches which enlarge and thicken

  • Treatment -penicillin or erythromycin



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Strep Throat

  • Most common of all Strep diseases

  • Spread by saliva or nasal secretions

  • Incubation period 2-4 days

  • Sore throat, slight fever (101)

  • Important to treat immediately to avoid post strep diseases


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Diagnosis and treatment of Strep Throat

  • Tell tale symptoms are slight fever associated with sore throat and visual of pus in back of throat

  • Quick diagnostic tests (Molecular) available but must be confirmed by throat swab and growth on blood agar (beta hemolysis)


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Diagnosis and treatment of Strep Throat

  • If the strain of S. pyogenes is lysogenic for a particular phage which expresses an erythrogenic toxin the result is Scarlet fever

  • Rash appears and characteristic is the strawberry colored tongue



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Treatment of Strep

  • Penicillin G or Erythromycin are drugs of choice

  • Although the disease is self-limiting it is important to treat immediately to avoid post strep complications


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Poststreptococcal diseases

  • Rheumatic Fever-autoimmune disease involving heart valves,joints, nervous system. Follows a strep throat

  • Acute glomerulonehritis or Bright’s Disease-inflamatory disease of renal glomeruli and structures involved in blood filter of kidney. Due to deposition of Ag/Ab complexes


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Rheumatic Fever

  • Most common cause of permanent heart valve damage in children

  • Exact cause not yet known but there appears to be some antibody cross reactivity between the cell wall of S. pyogenes and heart muscle


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Rheumatic Fever

  • Diagnosis is based on symptoms and is difficult

  • Occurs most frequently between ages of 6 and 15

  • US it is about 0.05% of pop having strep infections

  • 100x more frequent in tropical countries


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Rheumatic Fever

  • Treatment is via salicylates (aspirin derivatives) and corticosteroids to decrease inflammation and fever.


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Glomerular Nephritis

  • Diagnosis based on history of Strep throat and clinical findings.

  • Symptoms include fever, malaise,edema, hypertension and blood or protein in urine

  • Occurs in 0.5% of those having strep throat.


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Glomerular NephritisTreatment and Recovery

  • Penicillin or erythromycin to eradicate and residual strep infection

  • 80-90% of cases recover with bed rest lasting for months

  • Kidney damage in the remainder is often permanent resulting in chronic glomerular nephritis


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Streptococcus Pneumonia

  • Caused by infection with Streptococcus pneumoniae

  • Gram positive, alpha hemolytic, not of lancefield serotype A

  • Often part of normal flora of respiratory track and becomes infective once hosts resistance is lowered. Classified as an endogenous infection.



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Strep Pneumonia

S. pneumoniae

Alpha hemolysis


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Strep pneumonia

  • Predisposing factors: upper respiratory viral infection, diabetes, alcoholism

  • 60-80% of all pneumonias



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Cause of strep pneumonia

  • Primary virulence factor is the capsular polysaccharide which protects the organism against phagocytosis

  • Pathogenesis is due to rapid growth of bacteria in alveolar spaces


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Symptoms of Strep Pneumonia

  • Onset abrupt

  • Chest pains

  • Chills

  • Labored breathing


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Diagnosis of Strep pneumonia

  • Chest Xray

  • Culture and staining

  • Biochemical tests of isolated organism


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Treatment of Strep Pneumonia

  • Typically treated with Penicillin G cefotaxime, oflaxacin or for those allergic to penicillins can be treated with erythromycin or tetracycline

  • Pneumococcal vaccine (Pneumovax 23 or Pnu-immune 23) is available for the elderly


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Staphylococcal infections

  • One of the most common of all infections

  • Staphylococcus are divided into pathogens and non pathogens based on possession of the enzyme coagulase

    • Coagulase + are usually S. aureus and pathogenic

    • Coagulase - are organisms like S. epidermidis are less invasive



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Toxic Shock Syndrome

  • Most in women using superabsorbant tampons

  • Staphylococcus aureus-Gram positive cocci

  • Low blood pressure, fever, diarrhea, skin rash can be fatal


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Toxic Shock Syndrome

  • Symptoms mainly caused by toxic shock syndrome toxin 1(TSST1)

  • Several other enterotoxins also involved


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Staph skin infections

  • Most common cause of acne, boils, furuncle and cabuncles

  • Treatment can be difficult because of antibiotic resistance.Usually can be treated with methicillin, cephalosporins,or vancomycin

  • Methicillin resistant strains=MRSA


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Staph skin infections

Furuncle

(infected hair follicle

Deep folliculitis

superficialfolliculitis

Carbuncle

Multiple abcesses

Around many hair

follicles

Scalded skin

syndrome

Staph impetigo


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Scalded Skin Syndrome

  • Due to strains of S. aureus containing a special toxin-exfoliatin


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Diagnosis

  • Culture and stain-gram positive in grape-like clusters

  • Catalase and coagulase tests

  • DNA fingerprinting



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