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Introduction: Staphylcocci vs. Streptococci

Introduction: Staphylcocci vs. Streptococci . Chapter 18. Staphylococci. Genus Staphylococcus Gram positive Older cultures & clinical specimens may not stain true Growth in clusters Common inhabitant of skin and mucous membranes Grows between 10ºC and 46ºC Optimum temperature 37ºC

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Introduction: Staphylcocci vs. Streptococci

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  1. Introduction: Staphylcocci vs. Streptococci Chapter 18

  2. Staphylococci • Genus Staphylococcus • Gram positive • Older cultures & clinical specimens may not stain true • Growth in clusters • Common inhabitant of skin and mucous membranes • Grows between 10ºC and 46ºC • Optimum temperature 37ºC • Facultative anaerobe • Catalase positive • Lack spores • Lack flagella • May be encapsulated

  3. Staphylococci • 31 species are placed in this genus • Most important pathogen • S. aureus • Most serious pathogen • Coagulase positive • Role of coagulase in disease process unclear • Others associated with opportunistic infections • S. epidermidis • S. capitis • S. hominis • S. saprophyticus

  4. Staphylococcus aureus • Staphylococcus aureus • Most strains are metabolically versatile • Resistant to killing for a non-spore former • Osmotolerant – high salt MSA plates • Remains viable after months of air drying • Resists many disinfectants • Some stains are antibiotic resistant • Withstand 60ºC for 60 minutes • Many Exoenzymes & toxins

  5. Staphylococcus aureus • Staphylococcus aureus • Usual colonization not associated w/symptoms • Infection results from • Poor hygiene • Poor nutrition • Tissue injury • Pre-existing primary infections • Diabetes • Immunodeficiency • Pathogenicity arises from a combination of virulence factors

  6. Staphylococcus aureus • Scope of Clinical Disease • Depends on the degree of invasion • Depends on toxin production • Localized to systemic

  7. Localized Staph Infections • Stapnylococcus aureus • Invades skin through • wounds, follicles, or glands • Furuncle – boil • Carbuncle – cluster of boils into one mass • Both painful • Do not respond to therapy unless perforated and cleared of pus • Can lead to systemic infections if uncleared

  8. Systemic Staph Infections • Osteomyelitis • Infection of the bone • Necrosis or breakage of bony tissue • Painful swelling, fever & pain • Pneumonia • Multiple lung abscesses • Fever, chest pain & bloody sputum • Endocarditis • Meningitis

  9. Drug Resistant Staphylococcus arureus • Drug resistant strains • HA – MRSA • 80% of hospital staph infections • Resistance to all major drugs except vancomycin • A few reports of VRSA • CA – MRSA • Acquired through schools, prisons, & gyms • Sensitive to a wider array of antibiotics than HA – MRSA

  10. Streptococci • Genus Streptococcus • Gram positive • Grow in chains • Variable length • pairs are common • Facultative anaerobe • Catalase negative • Peroxidase system for inactivating hydrogen peroxide • Lack spores • Lack flagella • Have capsules (HA) or form slime layers • Sensitive to drying, heat, disinfectants & drugs • Normal residents or agents of disease in humans and animals; some are free living

  11. Streptococci • Streptococci classification • Confusing – three different methods • Hemolytic pattern • α, β, or γ • Strep grown on blood agar w/different results • Group – cell wall carbohydrates (antigens) of various cultures stimulated different antibodies (Lancefield) • A, B, C, G & D • All these groups show β hemolysis on blood agar • Species – biochemical & DNA tests • In clinical labs all three methods may be used to assist in identification

  12. LG = Lancefield Group UTI = Urinary tract infection RT = Respiratory tract

  13. Beta-Hemolytic Streptococcus pyogenes • Streptococcus pyogenes • Also known as Group A Strep (GAS) • Most serious streptococcal pathogen • Usually local infection at site of initial entry • Aggressive stains, virulence factors and toxins can lead to systemic disease

  14. Examples ofαandγ Hemolysins Greenish ting Heme group not broken down agar remains red color

  15. Beta-Hemolytic Streptococcus pyogenes • Streptococcus pyogenes • Unable to penetrate intact skin • Adhesion to epithelial cell surface • Bacterial surface proteins • M protein • Also prevents opsonization by binding to fibrinogen • Gains entry through • Small breaks in skin • Abrasions & wounds • Chickenpox lesions • bites

  16. View of GAS • C5a protease • Inactivates complement • M protein • Adhesion • Binds to fibrinogen to prevent phagocytosis • Capsule • In early infection may be degraded by hyaluronidase for increased adhesion • Prevents phagocytosis • C carbohydrates • Basis for Lancefield groups • Protection against lysozyme C5a protease M C

  17. Beta-Hemolytic Streptococcus pyogenes • Superficial infections • Skin • Superficial – Impetigo or pyoderma • Invasive – cellulitis or erysipelas • Pharynx • Pharyngitis – strep throat • Tonsillitis

  18. Beta-Hemolytic Streptococcus pyogenes • Systemic Infections • Strep throat can become scarlet fever • Prophage encodes for erythrogenic toxin • Systemic spread of toxin • High fever • Bright red rash on face, trunk, & inner arms/legs • After 10 days fever subsides • Sloughing of epidermis

  19. Diseases caused by group A streptococci (GAS). GAS cause a wide spectrum of diseases throughout the human body. The suppurative diseases (labeled in black) are caused by direct damage by the organism and the secreted exoenzymes of GAS. The nonsuppurative sequelae of GAS infection (labeled in bold) are late manifestations caused by a self-directed immune response. The toxin-mediated diseases (labeled in italics) are caused by streptococccal exotoxins that are secreted into the bloodstream

  20. Beta-Hemolytic Streptococcus pyogenes • Long term complications of GAS • Tissues are injured due to invasion & toxins • Also severe damage due to autoimmune cross reactions • Inflammation and cell killing due to your immune system • Rheumatic fever • Carditis • Chorea • Heart valve replacements – middle age • Acute glomerulonephritis • Kidney cells so damaged they do not filter blood • Most cases heal spontaneously, some become chronic • Nephritis • Increased BP • RBCs and WBCs in urine

  21. Beta-Hemolytic Streptococcus agalactiae • GBS – Group B Strep • Frequent inhabitant of cattle • Bovine mastitis – inflammation of mammary • Has now colonized humans • Vagina • Pharynx • Large intestine • GBS can be transferred to infant in delivery • Cause of neonatal pneumonia • Sepsis • Meningitis • Pregnant women are screened in 3rd trimester

  22. Alpha – Hemolytic Streptococci • Also known as the Viridans Group • Most numerous residents of oral cavity • Can cause opportunistic infections • Most lack full complement of toxins and exoenzymes • Not highly invasive • Dental procedures can lead to • Meningitis • Abdominal infection • Tooth abscesses • Endocarditis – subacute not chronic

  23. Staph vs. Strep Identification If a selective media is used, such as MSA then the only growth on the plate will be Staph. However, if a non-selective media is used then heterogeneous growth is present. Staph and Strep can be easily distinguished from each other using certain biochemical tests. Staph is always catalase positive, Strep is not. S. aureus is distinguished from other Staph species using the coagulate test. Strep can be further characterized using blood agar and hemolysin reactions

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