Streptococcal Diseases

Streptococcus pyogenes

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

Gram Stain of S. pyogenes

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

S.pyogenes S. pneumonia

Beta hemolysisAlpha hemolysis

Diseases caused by S. pyogenes

• Strep throat • Impetigo• Erysipelas• Cellulitis• Invasive Strep A infections

– Necrotizing fasciitis– Myositis– Toxic shock-like syndrome

Erysipelas

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

• Painful red patches which enlarge and thicken

• Treatment -penicillin or erythromycin

Erysipelas

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

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)

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

Strawberry Tongue

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

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

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

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

Rheumatic Fever

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

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.

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

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.

Strep Pneumonia

Strep Pneumonia

S. pneumoniaeAlpha hemolysis

Strep pneumonia

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

• 60-80% of all pneumonias

Strep Pneumonia

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

Symptoms of Strep Pneumonia

• Onset abrupt

• Chest pains

• Chills

• Labored breathing

Diagnosis of Strep pneumonia

• Chest Xray

• Culture and staining

• Biochemical tests of isolated organism

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

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

Diseases of Staphylococcus

Toxic Shock Syndrome

• Most in women using superabsorbant tampons

• Staphylococcus aureus-Gram positive cocci

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

Toxic Shock Syndrome

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

• Several other enterotoxins also involved

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

Staph skin infections

superficialfolliculitis

Deep folliculitis

Furuncle(infected hair follicle

CarbuncleMultiple abcessesAround many hairfollicles

Staph impetigoScalded skinsyndrome

Scalded Skin Syndrome

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

Diagnosis

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

• Catalase and coagulase tests

• DNA fingerprinting

S. aureus