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
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
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
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
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
• Predisposing factors: upper respiratory viral infection, diabetes, alcoholism
• 60-80% of all pneumonias
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
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
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
Diagnosis
• Culture and stain-gram positive in grape-like clusters
• Catalase and coagulase tests
• DNA fingerprinting