Commensal Bacteria and Infection Overview
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Questions and Answers

Which type of toxin is associated with being produced by gram-negative bacteria?

  • Exotoxins
  • Endotoxins (correct)
  • Cytotoxins
  • Neurotoxins
  • What is the primary composition of exotoxins?

  • Peptidoglycan
  • Lipopolysaccharides
  • DNA
  • Proteins (correct)
  • What is the main action of endotoxins when released into the body?

  • Induce high titer of antitoxin
  • Generalized non-specific toxic effects (correct)
  • Specific receptor binding
  • Cause specific organ failure
  • Which specific feature distinguishes exotoxins from endotoxins in terms of their heat stability?

    <p>Exotoxins are labile at 60°C</p> Signup and view all the answers

    Which type of toxin is known for causing endotoxic or septic shock?

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

    Which organism is known to produce exotoxins?

    <p>Clostridium diphtheriae</p> Signup and view all the answers

    What characteristic is associated with the immunogenicity of exotoxins?

    <p>Induce high titer of antitoxin</p> Signup and view all the answers

    What do exotoxins and endotoxins have in common regarding their origin?

    <p>Both can cause similar symptoms</p> Signup and view all the answers

    Which characteristic defines an ideal antibacterial?

    <p>Selective target with narrow spectrum</p> Signup and view all the answers

    Which method determines the minimum inhibitory concentration (MIC) of an antibiotic?

    <p>Microbroth dilution method</p> Signup and view all the answers

    What is NOT a complication of antimicrobial chemotherapy?

    <p>Improved immune response</p> Signup and view all the answers

    Which of the following best describes chemoprophylaxis?

    <p>Administration of medication to prevent infection</p> Signup and view all the answers

    What does the standardization of bacterial inoculum entail in susceptibility testing?

    <p>Diluting the bacteria to 0.5 McFarland turbidity standard</p> Signup and view all the answers

    Which of the following methods is NOT a quantitative method for antibiotic susceptibility testing?

    <p>Qualitative susceptibility tests</p> Signup and view all the answers

    What type of bacteria exclusively metabolize anaerobically but are insensitive to the presence of O2?

    <p>Aerotolerant anaerobes</p> Signup and view all the answers

    Which category of microorganisms prefer neutral pH for optimal growth?

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

    What is a common procedure in macro-broth dilution tests?

    <p>Standardizing inoculum with 0.5 McFarland turbidity</p> Signup and view all the answers

    What is a desirable characteristic of an antibiotic regarding resistance?

    <p>Emergence of resistance is slow</p> Signup and view all the answers

    What type of bacteria requires oxygen levels below 0.2 atmospheres for optimal growth?

    <p>Microaerophilic bacteria</p> Signup and view all the answers

    What is the optimal growth temperature range for thermophiles?

    <p>45 to 70 degrees Celsius</p> Signup and view all the answers

    Which of the following describes psychrotrophs?

    <p>Organisms with an optimum temperature of 10-15 degrees Celsius</p> Signup and view all the answers

    What term refers to microorganisms that thrive in environments with high salt concentrations?

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

    Which of the following describes the metabolism of obligate anaerobes?

    <p>They cannot tolerate O2 and rely on fermentation.</p> Signup and view all the answers

    What is the primary method of growth for microorganisms classified as acidophiles?

    <p>Growth in acidic environments</p> Signup and view all the answers

    Which of the following statements about antiseptics is true?

    <p>They are safe for application on skin and mucous membranes.</p> Signup and view all the answers

    What is the primary purpose of decontamination?

    <p>To reduce pathogenic microorganisms to safe handling levels.</p> Signup and view all the answers

    What is true about dry heat sterilization?

    <p>It is a cost-effective method but less corrosive.</p> Signup and view all the answers

    What is the characteristic of moist heat sterilization at 100 oC?

    <p>It can kill vegetative bacteria and hepatitis B virus.</p> Signup and view all the answers

    Which method is the best example of pasteurization?

    <p>Heating at 63 oC for 30 minutes.</p> Signup and view all the answers

    What pressure condition is required for steam sterilization using an autoclave?

    <p>Above atmospheric pressure.</p> Signup and view all the answers

    Which of the following is a limitation of boiling water for sterilization?

    <p>It does not kill all bacterial spores.</p> Signup and view all the answers

    What is the main method of sterilization used for glassware and metallic instruments?

    <p>Dry heat sterilization.</p> Signup and view all the answers

    What role do commensal bacteria in the gut play concerning pathogenic organisms?

    <p>They compete with pathogenic organisms for nutrition.</p> Signup and view all the answers

    Under which condition might commensal bacteria become harmful?

    <p>When host defense mechanisms are lowered.</p> Signup and view all the answers

    What is the primary difference between infection and disease?

    <p>Infection involves the entry of the parasite, while disease involves tissue destruction.</p> Signup and view all the answers

    Which of the following is NOT a mode of transmission for infections?

    <p>Transfusion of nutrients</p> Signup and view all the answers

    What is a characteristic of carriers in terms of disease transmission?

    <p>They can transmit the organism without showing manifestations.</p> Signup and view all the answers

    In what way can E. coli cause a urinary tract infection?

    <p>By reaching the renal system through blood or lymphatics.</p> Signup and view all the answers

    Which statement accurately describes a permanent carrier?

    <p>They carry the pathogenic organism without clinical manifestations over an extended period.</p> Signup and view all the answers

    What is a potential portal of exit for pathogens from the host?

    <p>Urine, stools, and respiratory discharges.</p> Signup and view all the answers

    Study Notes

    Commensal Bacteria

    • Commensal bacteria in the gut digest polysaccharides and produce certain vitamins.
    • They inhibit the growth of pathogenic organisms by competing for nutrients.
    • Under certain conditions, commensal bacteria can become pathogenic.
    • Conditions that can lead to commensal bacteria causing disease include:
      • Weakened immune systems (e.g., immunosuppressed, diabetic, or leukemic patients)
      • Alteration of host tissues (e.g., Streptococcus viridans, a normal inhabitant of the mouth and throat, can cause endocarditis in individuals with pre-existing heart lesions)
      • Changes in the natural habitat of the bacteria (e.g., E. coli, a normal resident of the intestine, can cause urinary tract infections if it enters the renal system via blood or lymphatics)

    Infection and Disease

    • Infection is the process of a parasite entering a relationship with a host.
    • Disease is the destruction of host tissues caused by parasite invasion, toxin production, or other virulence factors.
    • Factors required for disease development include:
      • Source of infection: Human, animal, or environmental (soil)
      • Mode of transmission: Insect bites, fecal contamination, inhalation of droplets, sexual contact, blood transfusion
      • Portal of entry: Gastrointestinal, genitourinary, or respiratory tracts, skin, mucous membranes, abrasions, insect bites, or injections
      • Parasite multiplication: Can occur locally at the portal of entry or spread through tissues, blood, or lymphatics to a target organ
      • Portal of exit: Urine, stools, respiratory or genital discharges, blood (transmitted by insects or injections)

    Carriers

    • Carriers are individuals who harbor a pathogenic organism without exhibiting clinical symptoms.
    • Carriers can transmit the organism to other susceptible individuals.
    • Carriers can be transient (during the incubation period) or permanent (chronic), as in hepatitis B.
    • Carriers are considered significant sources of infections for the following reasons:
      • They don't show signs of the disease.
      • They interact with the public without being recognized as carriers.
      • They can be classified into two groups:

    Toxins

    • Exotoxins:

      • Protein toxins secreted by living bacteria that diffuse into the surrounding medium (extracellular toxins).
      • Production of most exotoxins is controlled by genes found on plasmids or bacteriophages.
      • Exotoxins are highly specific in their actions and can be categorized as neurotoxins, enterotoxins, or cytotoxins based on their effects and target organs.
      • Examples: Cl. tetani exotoxin (plasmid-coded), C. diphtheriae and Cl. botulinum toxins (phage-coded)
    • Endotoxins:

      • Integral components of the cell wall of gram-negative bacteria.
      • Released when the bacteria die and disintegrate.
      • Toxicity is associated with the lipid portion of the endotoxin.
      • Organisms producing endotoxins include E. coli and Meningococci.
      • Endotoxins are primarily responsible for endotoxic or septic shock.
      • They cause generalized, non-specific toxic effects like fever, hypotension, disseminated intravascular coagulation (DIC), shock, and potentially death due to organ failure.

    Key Differences Between Exotoxins and Endotoxins

    Property Exotoxins Endotoxins
    Location of Genes Plasmid or bacteriophage Bacterial chromosome
    Composition Proteins Lipopolysaccharides
    Action Specific (binds to specific receptors on specific host cells), No fever Non-specific (fever and shock), No specific receptors
    Heat Stability Labile, destroyed at 60°C. Stable at 100°C for 1 hr Stable, resistant to heat
    Diffusibility Diffusible, Excreted by living cells Not diffusible, Integral part of the cell wall
    Immunogenicity Strong, induce high titer of antitoxin Weak immunogenicity
    Toxicity Strong Weak
    Convertibility to Toxoid Yes No
    Produced by Gram-positive bacteria mainly Gram-negative bacteria

    Other Noteworthy Points

    • Toxoid: A toxin treated (usually with formalin) to remove its toxicity while retaining its immunogenicity.
    • Peptidoglycans and teichoic acids, released when gram-positive cells die, can also cause effects similar to endotoxins.

    Oxygen Requirements for Bacterial Growth

    • Obligate aerobes: Require oxygen for growth and die in its absence.
    • Obligate anaerobes: Cannot survive in the presence of oxygen.
    • Facultative anaerobes: Can grow with or without oxygen.
    • Aerotolerant anaerobes: Can tolerate oxygen but do not use it for metabolism.
    • Microaerophiles: Require low oxygen levels and high carbon dioxide concentrations for optimal growth.

    Effect of pH on Growth

    • Acidophiles: Thrive in acidic environments (optimum pH below 7.0).
    • Neutrophiles: Grow best at neutral pH (around 7.0).
    • Alkaliphiles: Prefer alkaline environments (optimum pH above 7.0).

    Effect of Temperature on Growth

    • Mesophiles: Grow optimally at temperatures near 37°C (human body temperature).
    • Thermophiles: Optimal growth between 45°C and 70°C.
    • Extreme thermophiles (hyperthermophiles): Some Archaea thrive at temperatures above 80°C, with maximum temperatures reaching 115°C.
    • Psychrophiles: Cold-loving organisms that can grow at 0°C.
    • Psychrotrophs: Similar to psychrophiles but have an optimal growth temperature between 10°C and 15°C.

    Water Availability and Bacterial Growth

    • Water activity: Represents the availability of water for cellular processes.
    • Halophiles: Microorganisms that require salt (NaCl) for growth.

    Ideal Antibacterial Properties

    • Selective target
    • Narrow spectrum (does not kill normal flora)
    • Minimal adverse reactions (toxicity, allergy)
    • Various routes of administration
    • Good absorption and distribution to the infection site
    • Slow emergence of resistance

    Complications of Antimicrobial Chemotherapy

    • Development of drug resistance
    • Drug toxicity
    • Superinfection
    • Hypersensitivity

    Chemoprophylaxis

    • Administration of medication to prevent disease or infection

    Antibiotic Susceptibility Testing

    • Quantitative Methods: Determine the minimum amount of antibiotic (minimum inhibitory concentration, or MIC) that inhibits the growth of a bacterial isolate. Methods include:

      • Broth dilution methods (macrobroth and microbroth)
      • Agar dilution methods
    • Qualitative Methods: Determine the susceptibility or resistance of a bacterial isolate to a specific antibiotic.

    • Automated Susceptibility Tests: Use automated systems to perform susceptibility testing. -Newer Non-Automated Susceptibility Tests: Include methods like E-tests and disc diffusion methods.

    • Molecular Techniques: Rapidly identify antibiotic resistance genes.

    Antiseptics

    • Chemical agents non-toxic to living tissues. They can be applied to skin and mucous membranes but not suitable for systemic administration. -Examples: ethyl alcohol, chlorohexidine

    Decontamination

    • Reduces pathogenic microorganisms so that items are safe to handle, use, or dispose of.
    • Methods of decontamination include cleaning, disinfection, and sterilization.

    Methods of Sterilization

    1. Sterilization by Heat:

      • Dry Heat: Kills by destructive oxidation of essential cellular components. Less efficient than moist heat but less expensive and non-corrosive.

        • Dry heat sterilizer: Isolated, double-walled chamber heated by electricity with a thermostat.
        • Temperature: 160°C for 2 hours or 170°C for 1 hour.
        • Used for glassware, ointments, powders, oils, and metallic instruments.
      • Moist Heat: Kills by protein denaturation.

        • Methods:
          • Moist heat below 100°C: Pasteurization (e.g., milk at 63°C for 30 min or 72°C for 15-20 sec followed by rapid cooling)
          • Moist heat at 100°C: Boiling for 20 min (kills vegetative bacteria and hepatitis B virus but not all bacterial spores)
          • Steam sterilization above 100°C: Autoclave
            • Closed chamber where pressure increases the boiling point of water above 100°C.
            • Kills all microorganisms, including spores.
            • Essential for sterilization of surgical instruments, lab equipment, and other materials requiring sterility.

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    Description

    This quiz explores the role of commensal bacteria in the gut, their benefits, and conditions under which they may become pathogenic. It also discusses the relationship between infection and disease, highlighting how parasites interact with hosts. Test your knowledge on these fundamental microbiological concepts.

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