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30 Cards in this Set
- Front
- Back
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Staphylococcus:
Gram neg/pos Shape |
Gram pos
Cluster forming Cocci (sphere) |
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Staph aureus:
Requirements for infection Gram neg/pos Shape Common Habitat |
Staph aureus - COCCUS
Gram pos Cluster Sphere Require sig host compromise or break in skin/insertion of foreign body Cause suppuration (PUS), abscess formation Anterior nares (external nostrils), perineum |
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Which staph infection is most virulent?
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AUREUS
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How is staph aureus different from other staph strains?
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Staph has coagulase (breaks
down fibrinogen-->fibrin to encapsulate itself) Has furuncles (boils) Has exotoxin production |
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How can staphylococcus be distinguished from streptococcus?
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Catalase test
Staph has catalase!!! (H2O2-->H2O + O2) |
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What are the surface proteins of S. aureus? Role?
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Teichoic Acid: mediates attachment to mucosal surfaces via binding to fibronectin
Protein A: binds Fc of IgG for antiphagocytic effect |
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What are the cytolytic exotoxins of S. aureus? Effects?
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alpha-toxin (hemolysin): disrupts smooth muscle in BV's (toxic to cells via creating pores in membranes)
Panton-Valentine Leukocidin: found in 50% of s. aureus strains; lethal to PMN (polymorphonuclear lymphocytes) |
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What are the superantigen exotoxins of S. aureus? Effects?
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Gen: superantigen exotoxins damage host tissues or provoke syx of disease; bind MHC II complex and cause T cell to release large amounts of cytokines leading to major systemic effects
Toxic Shock Syndrome Toxin (TSST-1) Enterotoxins: when bact grow in food and produce toxin; ingestion causes food poisoning (stimulates vomiting center in brain) |
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Effects of exfoliative exotoxin? Released by?
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Released by S. aureus
Causes SCALDED SKIN SYNDROME in children (blistering of skin by attacking intracell jns) Localized IMPETIGO |
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What is impetigo? Cause?
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A contagious skin infection caused by streptococcal bacteria, forming pustules and yellow, crusty sores.
AKA PYODERMA |
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What staphylococcal enzymes promote immunologic evasion?
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Coagulase (formation of fibrin layer around abscess to protect from phagocytosis)
Catalase (enhances survival in phags) |
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What staphylococcal enzymes promote spread in tissues?
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INVASINS
Hyaluronidase (hydrolyes hyaluronic acid on CT) Staphlokinase: dissolves fibrin clots Lipases: hydrolyze lipis (for sebaceous area survival, invasion of cut/subcut tissue) |
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What staphylococcal enzymes promote resistance to antimicrobial agents?
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PENICILLINASE (BETA-LACTAMASE)
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MecA gene:
Function Method of Transfer |
Resistance to PCN (codes for
Spread via CONJUGATION (horizontal gene transfer |
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Streptococcus:
Gram neg/pos Shape |
Strep:
Gram pos Cocci in CHAINS (not grapes!) |
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How are sreptococci classified? (3 types)
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Via hemolysis on bloog agar:
alpha-hemolytic: partial clearing with green Hg beta-hemolytic: complete clearing, gross lysis of RBC's, clear ring around colony (DUE TO EXOTOXIN: STREPTOLYSIN( Gamma-hemolytic: no clearing, no color change, non-hemolytic |
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Lancefield antigens:
Found primarily in ___-hemolytic streprocci Most important groups are ________ |
Lancefield:
found primarily in beta-hemolytic strep Most impt grps are A (S. pyogenes) and B (S. agalactiae) |
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Streptococcus pyogenes:
Group of Strep (A/B) Method of Infection |
Group A Strep (GAS)
Invades intact skin/mucous membranes (part of normal flora, infects when defenses are down) Adherence is crucial for initiating dz (cell wall surface!!) |
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What surface proteins of streptococcus pyogenes allow for infection?
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M Protein: Promotes antigenic variability (used to differentiate strains); binds fibrinogen and blocks binding of complement
Protein F: fibronectin-binding protein |
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Which surface protein of s. pyogenes is associated with Rheumatic Fever?
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M Protein (can contain antigenic epitopes related to heart muscle and may lead to autoimmune rheumatic carditis--rheumatic fever)
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Is the capsule of streptococcus pyogenes antigenic? Why or why not?
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Not antigenic bc composed of HYALURONIC ACID (chemically similar to that of host CT); promotes immune evasion (antiphagocytic)
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How does streptococcus pyogenes prevent chemotaxis?
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Secretes C5a peptidase which inactivates complement, interfering with mobilization of WBCs
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Streptococcal pyrogenic exotoxins:
Are both toxins and ______ Which subtype is responsible for necrotizing fasciitis (invasive infection)? |
Streptococcal pyrogenic exotoxins act as Superantigens
SpeA (pyrogenic exotoxin A) exhibit effects like staph TSS |
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What are erysepelas?
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infection of dermal layer (aggressive)
Fiery reddish patches with raised margins |
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What is cellulitis?
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Destruction of solid tissue
(invasive bacteremia) |
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What is myositis?
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Destruction of muscle
(invasive bacteremia) |
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What is necrotizing fasciitis?
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Deep local invasion with fascia destruction (invasive bacteremia)
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Symptoms of Scarlet Fever?
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strep throat with sunburn-like rash
(a toxigenic manifestation) |
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What is strep throat? Symptoms?
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acute inflammation of pharynx and tonsils may have local necrosis/abscess formation
Syx: INFLAMMATION OF OROPHARYNX PETECHIAE ON SOFT PALATE |
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Streptococcal Toxic Shock-Like Syndrome:
Cause Symptoms |
GAS! (GROUP A STREP)
Diffuse rash, fever, exfoliation, vascular collapse Necotizing fasciitis/myositis (FLESH-EATING BACTERIA) |
