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 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 hemolysis Alpha 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 Nephritis Treatment 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. pneumoniae Alpha 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 Furuncle (infected hair follicle Deep folliculitis superficialfolliculitis Carbuncle Multiple abcesses Around many hair follicles Scalded skin syndrome Staph impetigo

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