Bacterial Culture and Catalase Test
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Bacterial Culture and Catalase Test

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Questions and Answers

Which Staphylococcus species is most clinically important?

  • Staphylococcus aureus (correct)
  • Staphylococcus saprophyticus
  • Staphylococcus epidermidis
  • Staphylococcus lugdunensis

    • What can high concentrations of PVL cause in relation to PMNs?

  • Direct necrotic effect on epithelial cells
  • Lysis of PMNs (correct)
  • Apoptosis of PMNs
  • Tissue necrosis without inflammatory response

    • What is an effect of low concentrations of PVL on PMNs?

  • Apoptosis of PMNs (correct)
  • Direct necrosis of epithelial cells
  • Enhanced proinflammatory response
  • Lysis of PMNs

    • What is the role of coagulase in Staphylococcus aureus?

    <p>Initiating fibrin polymerization</p> Signup and view all the answers

    What is an anti-phagocytic characteristic of Staphylococcus aureus derived from?

    <p>Fibrin deposition on its surface</p> Signup and view all the answers

    Which illness is commonly associated with Staphylococcus aureus?

    <p>Toxic shock syndrome</p> Signup and view all the answers

    Which characteristic is synonymous with the invasive pathogenic potential of Staphylococcus aureus?

    <p>Production of coagulase</p> Signup and view all the answers

    What can result from the release of granule contents from lysed PMNs?

    <p>Induction of an inflammatory response</p> Signup and view all the answers

    What is the primary mode through which herbivores acquire anthrax?

    <p>Ingestion of bacteria from the soil</p> Signup and view all the answers

    Which genetic material encodes the genes responsible for the protective agent in anthrax?

    <p>pXO1 plasmid</p> Signup and view all the answers

    What combination produces the edema toxin in anthrax?

    <p>PA + EF</p> Signup and view all the answers

    Which of the following is NOT a way humans can acquire anthrax?

    <p>Ingestion of contaminated water</p> Signup and view all the answers

    What is the major virulence factor of anthrax?

    <p>Lethal factor</p> Signup and view all the answers

    What effect does the edema toxin have on tissues?

    <p>It causes cell and tissue edema.</p> Signup and view all the answers

    Which statement about the anthrax cycle is true?

    <p>It includes contamination of infected meat.</p> Signup and view all the answers

    What is the function of the edema factor in anthrax virulence?

    <p>It acts as an adenylate cyclase.</p> Signup and view all the answers

    Which combination leads to the formation of lethal toxin in anthrax?

    <p>PA + LF</p> Signup and view all the answers

    What is considered a rare mode of transmission for anthrax?

    <p>Vector-borne transmission</p> Signup and view all the answers

    What is the primary action of pyrogenic exotoxins produced by Group A β-hemolytic Streptococci?

    <p>They transform plasminogen into plasmin.</p> Signup and view all the answers

    Which condition is most directly associated with pyrogenic exotoxins?

    <p>Scarlet fever</p> Signup and view all the answers

    What type of culture is specifically used to identify nasal carriers of Staphylococcus aureus?

    <p>Mannitol Salt Agar</p> Signup and view all the answers

    What result indicates that catalase is present in a specimen during the catalase test?

    <p>Bubbles are produced</p> Signup and view all the answers

    What is the role of pyrogenic exotoxins as superantigens?

    <p>They stimulate T cells by binding to class II MHC.</p> Signup and view all the answers

    What is the primary method used by commercially-available rapid test kits for detecting bacterial antigens?

    <p>Enzyme immunoassay or agglutination tests</p> Signup and view all the answers

    Which organism is classified as catalase-negative?

    <p>Streptococcus sp.</p> Signup and view all the answers

    Which of the following statements about SpeA is correct?

    <p>It is produced by Group A Strep. that carry a lysogenic phage.</p> Signup and view all the answers

    How sensitive are the antigen detection tests compared to culture methods?

    <p>60-90%</p> Signup and view all the answers

    What kind of specimens are typically used with Mannitol Salt Agar?

    <p>Contaminated specimens with mixed microbiota</p> Signup and view all the answers

    What is the specificity range of antigen detection tests in comparison to culture methods?

    <p>98-99%</p> Signup and view all the answers

    How long should Blood Agar Plates be incubated to see colonies of Staphylococcus species?

    <p>18 hours at 37°C</p> Signup and view all the answers

    Which of the following best describes the extraction method used by rapid test kits?

    <p>Enzymatic or chemical methods to extract antigen</p> Signup and view all the answers

    Which substance acts as a fibrinolysin in streptococcal infections?

    <p>Streptokinase</p> Signup and view all the answers

    What is the role of hydrogen peroxide in the catalase test?

    <p>It is the substrate broken down by catalase</p> Signup and view all the answers

    What could be a limitation of rapid antigen detection tests?

    <p>Lower sensitivity compared to culture methods</p> Signup and view all the answers

    What is the effect of pyrogenic exotoxins on blood clots?

    <p>They allow bacteria to escape from blood clots.</p> Signup and view all the answers

    What is the primary mechanism through which pyrogenic exotoxins interfere with the immune response?

    <p>They inhibit non-specific serum inhibitors and antistreptokinase.</p> Signup and view all the answers

    Which of the following is NOT a characteristic of streptococcal toxic shock syndrome?

    <p>It leads to immediate bacterial lysis.</p> Signup and view all the answers

    Which type of agar is used to recover Staphylococcus aureus from respiratory specimens?

    <p>Mannitol Salt Agar</p> Signup and view all the answers

    What is the main function of the catalase test in differentiating bacterial species?

    <p>To detect enzyme activity</p> Signup and view all the answers

    Study Notes

    Bacterial Culture Techniques

    • Catalase Test: Identifies Staphylococcus species by detecting cytochrome oxidase enzymes; a drop of hydrogen peroxide on the specimen results in bubble formation if catalase is present.
    • Blood Agar Plates: Used to culture Staphylococcus species; colonies appear after 18 hours at 37°C; can indicate hemolysis and pigment production.
    • Mannitol Salt Agar: Screens for nasal carriers of Staphylococcus aureus; effective for contaminated specimens with mixed microbiota.

    Anthrax Cycle

    • Transmission to Herbivores: Acquired by ingestion of soil bacteria; humans can get infected via contaminated skin, inhalation, or consumption of infected meat.
    • Exotoxins: Compounds released by anthrax bacteria lead to tissue edema and death; encoded by pXO1 plasmid.
      • Protective Agent (PA): Binds to receptors for entry of Edema Factor (EF) and Lethal Factor (LF).
      • Edema Factor (EF): Forms edema toxin with PA, causing cell and tissue edema.
      • Lethal Factor (LF): Combines with PA to produce lethal toxin, the major virulence factor causing death.

    Staphylococcus aureus Characteristics

    • Most clinically significant staphylococcal species, often causing superficial infections (e.g., impetigo) or systemic illnesses (e.g., septicemia).
    • Coagulase-positive, associated with toxigenic illnesses such as Toxic Shock Syndrome (TSS) and food poisoning.
    • Common causative agent of infective endocarditis.

    Pyrogenic Exotoxins

    • Function: Transforms plasminogen to plasmin, allowing bacteria to evade blood clots; interferes with serum inhibitors.
    • Produced by Group A, β-hemolytic Streptococci; similar to exfoliative toxins.
    • Linked to serious conditions like streptococcal toxic shock syndrome and scarlet fever; acts as superantigens, provoking cytokine release, shock, and tissue injury.

    Antigen Detection Tests

    • Rapid test kits utilize enzymatic or chemical methods to extract antigen from swabs; enzyme immunoassay or agglutination tests demonstrate the presence of antigens.
    • High sensitivity (60-90%) and specificity (98-99%) compared to traditional culture methods.

    Medically Important Staphylococci

    • Staphylococcus aureus: Key pathogen with coagulase production.
    • Staphylococcus epidermidis: Linked to nosocomial infections.
    • Staphylococcus saprophyticus: Known for urinary tract infections.
    • Staphylococcus lugdunensis: Associated with more severe infections compared to other coagulase-negative staphylococci.

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    Description

    This quiz explores the process of bacterial culture and diagnostic techniques for identifying Staphylococcus species. It includes details on the catalase test and the hydrolyzation of peroxide. Test your knowledge of microbiology and bacterial identification methods.

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