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16 Cards in this Set
- Front
- Back
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Morphology |
Spherical cocci 1 micron in diameter Arranged in a grape like cluster Non motile Non sporing Young cultures have visible capsules Gram positive |
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Why do they form clusters? |
Because cell division occurs in three planes and daughter cells tend to remain in close proximity. |
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Resistance |
Uniformly resistance to lysozymes. Sensitive to lysostaphin Were uniformly resistant to penicillin during pre-antibiotic era. |
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Type of resistance |
Beta lactamase mediated. Altered target site PBP2a Tolerance to penicillin Vancomycin resistance (VRSA) Vancomycin intermediate resistance (VISA)
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Penicillinase-resistant penicillins? |
Methicillin and Cloxacillin |
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Beta lactamase inhibitor penicillin |
Amoxicillin-clavulanic acid |
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MRSA |
- methicillin resistant S. aureus. - regulated by staphylococcus cassette chromosomal mec genes - based on the type of gene: a) Hospital-acquired MRSA - HA MRSA, the genes has types I, II, III and are multi-drug resistant. b) Community acquired MRSA - CA MRSA, gene is type IV , less resistant, more likely to produce PVL toxin and more transmissible |
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Pathogenicity and virulence |
Produce two types of disease - infection and intoxication. Infection - gains access to damaged skin, mucosal or tissue sites -> colonize by adhering to cells or ECM -> evade host defence mechanism & multiply & cause tissue damage. Intoxication - due to the toxins produced.
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Cell-associated factors |
Cell-associated polymers Cell surface proteins |
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Cell-associated polymers |
- Cell wall polysaccharide peptidoglycan activates complement and induces release of inflammatory cytokines. - Teichoic acid is an antigenic component of the cell wall and facilitates adhesion to the host cell and protects it from complement-mediated-opsonisation. - Capsular polysaccharide inhibits opsonisation. |
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Cell surface proteins |
Protein A - is chemotactic, anti phagocytic, anti-complementary, damages platelets and induces hypersensitivity. It binds to the Fc terminal of IgG, leaving Fab region free to combine with its specific antigen. If it's coated with IgG antiserum, it will be agglutinated when mixed with corresponding antigen - co-agglutination
Clumping factor - a surface protein, bound coagulase - responsible for slide coagulase test.
Possess protein receptors for proteins like fibronectin, fibrinogen, IgG and C1q - facilitate adhesion to host cells and tissues |
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Extracellular enzymes |
Coagulase - acts with CRF by binding to prothrombin and converting fibrinogen to fibrin. Basis of tube coagulase test
Lipid hydrolases - help them infect the skin and subcutaneous tissues by producing lipases
Hyaluronidase - breaks down connective tissue. Staphylokinase, fatty acid modifying enzymes, proteases - initiate and spread infection.
Nuclease - A heat stable DNase is a characteristic of S. aureus and helps in its identification. |
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Toxins |
Alpha hemolysin - inactivated at 70°C but paradoxically reactivated at 100°C - because at 60-70°C, toxin combines with heat labile inhibitor which denaturates at 100°C, leaving the toxin free. - it is toxic to macrophages, lysosomes, muscle tissues, renal cortex and circulatory system.
Beta hemolysin - exhibits hot-cold phenomenon
Gamma hemolysin - composed of two seperate proteins.
Delta hemolysin - has a detergent like effect on the cell membranes of erythrocytes, leucocytes, macrophages and platelets. |
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Panton-Valentine Leucocidin |
- two component toxin - composed of S and F components. - synergohymenotropic toxins |
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Enterotoxin |
- Responsible for manifestations of staphylococcal food poisoning. - symptoms: nausea, vomiting, diarrhoea after 2 to 6 hours of consumption of contaminated food. - heat stable toxin - resists 100°C for 10 to 40 minutes - food on which they grow - meat, fish, milk and milk products. - source of infection - food handler who is a carrier. - recovery is seen in a day. - eight antigenic types are known - A, B, C1, C2, C3, D, E, H. - acts directly in ANS - toxin is antigenic and neutralised by specific antitoxin - type A toxin is most common - serological tests like latex agglutination and ELISA are available for detection of toxin - also exhibits pyrogen, mitogenic, hypotensive, thrombocytopenic and cytotoxic effects. |
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Toxic shock syndrome toxin |
Y |
