Microbiology W3-2
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Questions and Answers

Which of the following describes the function of keratin in the skin?

  • It acts as a moisturizer to maintain skin hydration.
  • It facilitates the absorption of nutrients through the skin.
  • It serves as a low pH barrier against pathogens.
  • It forms the structural foundation of hair and nails. (correct)
  • Which of the following bacterial species is not typically found in normal skin microbial flora?

  • Corynebacterium species
  • Escherichia coli (correct)
  • Propionibacterium acnes
  • Staphylococcus epidermidis
  • What distinguishes β-hemolytic streptococci from other types?

  • They form clusters in cultures.
  • They produce lactic acid and are catalase-positive.
  • They are primarily anaerobic organisms.
  • They are classified by carbohydrate antigens in their cell walls. (correct)
  • Which characteristic is true about Streptococcus pyogenes?

    <p>It is classified under Lancefield group A.</p> Signup and view all the answers

    What is the primary defense function of sebum?

    <p>To suppress the growth of pathogenic microorganisms.</p> Signup and view all the answers

    Which of the following statements is true regarding the metabolic activity of streptococci?

    <p>They are commonly isolated using blood-enriched media.</p> Signup and view all the answers

    Which of the following best defines medical microbiology?

    <p>The interactions between animals and microorganisms, focusing on diseases.</p> Signup and view all the answers

    What type of infection arises from microorganisms originating from external sources?

    <p>Exogenous infection</p> Signup and view all the answers

    Which type of pathogen is always associated with human disease?

    <p>Strict pathogens</p> Signup and view all the answers

    In what settings are nosocomial infections typically acquired?

    <p>In a hospital environment</p> Signup and view all the answers

    Why are opportunistic pathogens particularly concerning for patients with defective immune systems?

    <p>They thrive in normal body settings without causing disease.</p> Signup and view all the answers

    What is a blood agar plate primarily used for?

    <p>To support the growth of fastidious organisms.</p> Signup and view all the answers

    Which component in blood agar plates helps in enriching the medium?

    <p>Defibrinated blood</p> Signup and view all the answers

    What pH range is desired for the nutrient agar in blood agar plates?

    <p>7.2 to 7.6</p> Signup and view all the answers

    At what temperature should the mixture be autoclaved for preparing blood agar plates?

    <p>121 °C for 15 minutes</p> Signup and view all the answers

    What is the primary purpose of Chocolate agar?

    <p>To grow fastidious respiratory bacteria</p> Signup and view all the answers

    Which type of hemolysis indicates complete lysis and digestion of red blood cells?

    <p>β-hemolysis</p> Signup and view all the answers

    Which of the following correctly describes γ-hemolysis?

    <p>No hemolysis occurring at all</p> Signup and view all the answers

    What common mechanism can compromise the skin barrier leading to SSTIs?

    <p>Surgical procedures</p> Signup and view all the answers

    What structure is found in the dermis layer of the skin?

    <p>Nerve endings</p> Signup and view all the answers

    In the context of SSTIs, what does the term 'soft tissue' refer to?

    <p>Connective and supporting tissues</p> Signup and view all the answers

    What is a common clinical challenge related to SSTIs?

    <p>Differentiating between severe and less severe cases</p> Signup and view all the answers

    What is a characteristic of the epidermis layer of skin?

    <p>Formed primarily of keratinocytes</p> Signup and view all the answers

    What condition can commonly lead to a break in the skin barrier, resulting in potential SSTIs?

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

    Which component is NOT typically found in the hypodermis layer of skin?

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

    What is the primary characteristic of necrotizing fasciitis?

    <p>Deep infection involving destruction of muscle and fat layers.</p> Signup and view all the answers

    Which virulence factor is primarily associated with the ability of S. pyogenes to invade host cells?

    <p>M protein</p> Signup and view all the answers

    Which condition is characterized by localized pain, inflammation, and systemic symptoms related to skin infection?

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

    Which of the following factors contributes to the virulence of Streptococcus pyogenes by enabling it to evade the immune response?

    <p>C5a peptidase</p> Signup and view all the answers

    What common characteristic is shared among most species of Staphylococcus?

    <p>They are non-motile and grow in clusters.</p> Signup and view all the answers

    In compound skin infections, what is a defining feature of cellulitis?

    <p>Involvement of subcutaneous tissues.</p> Signup and view all the answers

    What is a key clinical presentation of Streptococcal toxic shock syndrome?

    <p>Multiorgan systemic involvement with bacteremia.</p> Signup and view all the answers

    What is primarily responsible for the yellow or gold color of aureus colonies?

    <p>Carotenoid pigments</p> Signup and view all the answers

    Which of the following diseases is associated with scalded skin syndrome?

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

    What is a recognized virulence factor of Staphylococcus aureus that aids in evading the immune response?

    <p>Coagulase enzyme</p> Signup and view all the answers

    What type of toxin is responsible for the massive release of cytokines causing hypotension and shock in toxic shock syndrome?

    <p>Toxic shock syndrome toxin-1</p> Signup and view all the answers

    Which of the following is NOT a systemic disease associated with Staphylococcus aureus?

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

    What characteristic of Staphylococcus aureus allows it to survive for extended periods on dry surfaces?

    <p>Absence of an outer membrane</p> Signup and view all the answers

    Which method is used by the exfoliative toxin of aureus to interact with the immune system?

    <p>Binding to MHC II molecules</p> Signup and view all the answers

    What does the term 'facultative anaerobe' imply about Staphylococcus aureus?

    <p>It can grow with or without oxygen.</p> Signup and view all the answers

    Which population is particularly affected by scalded skin syndrome?

    <p>Neonates and young children</p> Signup and view all the answers

    What is the main reason Pseudomonas aeruginosa is resistant to many antibiotics?

    <p>It mutates porin proteins that control antibiotic penetration.</p> Signup and view all the answers

    Which of the following environments is NOT typically associated with the presence of Pseudomonas aeruginosa?

    <p>Dry soil</p> Signup and view all the answers

    What characterizes the growth of Pseudomonas aeruginosa colonies on a blood agar plate?

    <p>A green pigmentation with β-hemolysis.</p> Signup and view all the answers

    What is a significant risk factor for infections caused by Methicillin-resistant Staphylococcus aureus (MRSA)?

    <p>Presence of a foreign body.</p> Signup and view all the answers

    What is a common disease linked to infections from Pseudomonas aeruginosa?

    <p>Burn wound infections.</p> Signup and view all the answers

    Which of the following statements best describes the nutritional needs of Pseudomonas aeruginosa?

    <p>Has minimal nutritional requirements.</p> Signup and view all the answers

    What type of infectious transmission is primarily associated with the spread of MRSA?

    <p>Direct contact and exposure to contaminated objects.</p> Signup and view all the answers

    What characteristic of Pseudomonas aeruginosa contributes to its classification as an opportunistic pathogen?

    <p>It thrives in diverse environments and affects already weakened hosts.</p> Signup and view all the answers

    Which of the following is NOT a typical characteristic of Pseudomonas aeruginosa?

    <p>It relies on fermentation as its primary energy source.</p> Signup and view all the answers

    What range of diameters do aerosols produced by sneezing and coughing typically fall under?

    <p>1 to 1000 μm</p> Signup and view all the answers

    Which of the following diseases is caused by a bacterial pathogen that can be transmitted through aerosols?

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

    What is the primary method to decrease airborne disease transmission?

    <p>Wearing a face mask</p> Signup and view all the answers

    Which condition is NOT transmitted through aerosols?

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

    What type of colloid describes aerosols?

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

    Which of the following examples best illustrates an aerosol?

    <p>A suspension of pollen in air</p> Signup and view all the answers

    Which part of the respiratory tract is primarily responsible for the passage of air to the lungs?

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

    What factor significantly differentiates the infectious characteristics of the lepromatous and tuberculoid forms of disease?

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

    Which of the following organisms is least likely to be pathogenic when found in the upper respiratory tract?

    <p>Neisseria meningitidis</p> Signup and view all the answers

    What is the main function of the mucociliary clearance mechanism in the respiratory tract?

    <p>To trap and remove infectious particles</p> Signup and view all the answers

    How do goblet cells contribute to the defense mechanisms of the respiratory tract?

    <p>By secreting mucus</p> Signup and view all the answers

    What characteristic is true about the lower respiratory tract in terms of microorganism presence?

    <p>Generally considered sterile</p> Signup and view all the answers

    Which type of microorganism is predominantly found in the upper respiratory tract, according to quantity?

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

    What does the ciliary action in the mucociliary blanket accomplish?

    <p>Moves trapped particles toward the throat</p> Signup and view all the answers

    Which anatomical component follows the bronchi in the pathway of inhaled air?

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

    What is the size threshold for infectious particles to be efficiently trapped by the mucociliary blanket?

    <p>8-10 μm</p> Signup and view all the answers

    What is a primary characteristic of the lepromatous form of leprosy?

    <p>Disfiguring skin lesions and thickened dermis</p> Signup and view all the answers

    Which of the following best describes Mycobacterium leprae?

    <p>Obligate intracellular, weakly gram-positive rod</p> Signup and view all the answers

    What is a commonality between the reported cases of leprosy in 2005?

    <p>India, Nepal, and Brazil had the highest incidences</p> Signup and view all the answers

    How is leprosy primarily transmitted?

    <p>Person-to-person contact through respiratory secretions</p> Signup and view all the answers

    Which cellular immune response is observed in patients with tuberculoid leprosy?

    <p>Strong cellular immune reaction with lymphocytes</p> Signup and view all the answers

    What is a defining feature of Mycobacterium leprae that affects its culturing?

    <p>It is obligate intracellular and cannot be cultured artificially</p> Signup and view all the answers

    In the pathogenesis of leprosy, what characteristic distinguishes lepromatous leprosy from tuberculoid leprosy?

    <p>Increased bacterial load in macrophages</p> Signup and view all the answers

    Why might leprosy have a low reported incidence despite its historical prevalence?

    <p>Widespread use of effective therapy</p> Signup and view all the answers

    What type of staining is used to visualize Mycobacterium leprae due to its cell wall composition?

    <p>Acid-fast (Ziehl–Neelsen) staining</p> Signup and view all the answers

    Which of the following diseases is primarily characterized by inflammation of the tonsils?

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

    Which pathogen is known as the causative agent of whooping cough?

    <p>Bordetella pertussis</p> Signup and view all the answers

    What is a common feature of middle ear infections?

    <p>Ear drainage and pressure sensation</p> Signup and view all the answers

    Which of the following infections primarily affects infants and young children under two years of age?

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

    Which bacterium is commonly associated with ear infections?

    <p>Haemophilus influenzae</p> Signup and view all the answers

    What type of respiratory tract infection is characterized by inflammation of the larynx?

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

    Which pathogen is most likely to cause persistent bacterial infection in the lungs?

    <p>Mycobacterium tuberculosis</p> Signup and view all the answers

    Inflammation associated with the 'itis' suffix primarily indicates what in a disease context?

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

    What was a significant outcome of the Legionnaires' disease outbreak in 1976?

    <p>221 people were infected and 34 succumbed to the disease.</p> Signup and view all the answers

    Which of the following pathogens does NOT commonly cause respiratory tract infections?

    <p>E. coli</p> Signup and view all the answers

    Which of the following accurately describes the bacterium Legionella and its mechanism?

    <p>It prevents the fusion of phagolysosomes, aiding in replication.</p> Signup and view all the answers

    Why might Legionnaires' disease be mistaken for other illnesses?

    <p>Its symptoms share commonality with the flu and common cold.</p> Signup and view all the answers

    What is the primary mode of transmission for Legionnaires' disease?

    <p>Inhalation of aerosolized water containing the bacteria.</p> Signup and view all the answers

    What is a critical implication of failing to correctly diagnose Legionnaires' disease?

    <p>It can progress to severe pulmonary complications and death.</p> Signup and view all the answers

    Which types of environments are most likely to harbor Legionella bacteria?

    <p>Natural bodies of warm water and plumbing systems.</p> Signup and view all the answers

    What is the primary feature of the paroxysmal stage of whooping cough?

    <p>Repetitive coughing followed by inspiratory whoops</p> Signup and view all the answers

    Which treatment is most effective in decreasing the infectious stage of pertussis?

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

    Why are Legionella considered nutritionally fastidious organisms?

    <p>They require L-cysteine for growth</p> Signup and view all the answers

    What distinguishes the causative agent of Pontiac fever from other Legionella diseases?

    <p>It is nonfatal and resembles mild upper respiratory infections.</p> Signup and view all the answers

    Which of the following characterizes the lifecycle of Legionella bacteria?

    <p>They can survive in free-living amoebae in the environment</p> Signup and view all the answers

    What component in vaccines is crucial for eliciting an effective immune response against pertussis?

    <p>Inactivated pertussis toxin</p> Signup and view all the answers

    Which statement is true regarding the range of Legionella species?

    <p>Approximately half of the identified species are implicated in disease.</p> Signup and view all the answers

    In which stage does whooping cough display catarrhal symptoms resembling the common cold?

    <p>Catarrhal stage</p> Signup and view all the answers

    Which is a lesser-known complication linked to pertussis in adults?

    <p>Posttussive vomiting</p> Signup and view all the answers

    Which clinical feature is indicative of the convalescence stage of whooping cough?

    <p>Gradual reduction of coughing fits</p> Signup and view all the answers

    Study Notes

    Medical Microbiology

    • Medical microbiology is the study of interactions between animals (primarily humans) and microorganisms (bacteria, viruses, fungi, and parasites), focusing on diseases caused by these interactions.

    Infection Concepts

    • Exposure to an organism can lead to transient colonization, permanent colonization, or disease.
    • Exogenous infections arise from external sources.
    • Endogenous infections originate from the person's own microbes spreading to inappropriate sites.
    • Nosocomial infections are acquired in hospitals.

    Pathogen Types

    • Strict pathogens are always associated with human disease (e.g., Mycobacterium tuberculosis).
    • Opportunistic pathogens are normally part of the body's microbial flora but cause disease in compromised individuals (e.g., Staphylococcus aureus, Escherichia coli, Candida albicans).

    Bacterial Classification

    • Fastidious organisms require rich media, often containing blood components, to grow.

    Blood Agar Plate (BAP)

    • Enriched with mammalian blood (usually sheep or horse), typically at 5-10% concentration.
    • Components: 0.5% Peptone, 0.3% beef extract/yeast extract, 1.5% agar, 0.5% NaCl, distilled water.
    • pH should be from 7.2 to 7.6 (7.4).
    • Autoclave the mixture at 121°C for 15 minutes, let it cool to 45-50°C, and add 5% defibrinated blood.
    • Mix gently.

    Chocolate Agar (CHOC)

    • Type of blood agar where red blood cells are lysed by heating to 80°C.
    • Used to grow fastidious respiratory bacteria like Haemophilus influenzae.

    Hemolysis

    • Hemolysis is the lysis of red blood cells.
      • Alpha (α)-hemolysis: incomplete hemolysis.
      • Beta (β)-hemolysis: complete lysis and digestion of red blood cell contents.
      • Gamma (γ)-hemolysis: no hemolysis.

    Skin and Soft Tissue Infections (SSTIs)

    • Various presentations, etiologies, and severities involving microbial invasion of skin and underlying tissues.
    • Soft tissue includes: muscles, tendons, ligaments, fascia, nerves, fibrous tissues, fat, blood vessels, and synovial membranes.
    • Common entry points are breaks in the skin barrier: lacerations, bite wounds, scratches, instrumentation, pre-existing conditions (e.g., chicken pox, ulcers), burns, and surgery.
    • Diagnosing SSTIs requires differentiating life-threatening cases from less severe ones.

    Skin structure

    • Epidermis: outermost layer, containing keratinocytes (95%) and melanocytes.
    • Dermis: contains connective tissue, fibers, glycoproteins, nerve endings, hair follicles, glands, and blood vessels.
    • Hypodermis (subcutaneous tissue): attaches skin to bone and muscle, containing fibroblasts, macrophages, and adipocytes (fat).

    Natural Skin Defenses

    • Keratin: a protein forming the basis of horny epidermal tissues (hair, nails).
    • Skin cell shedding and regeneration.
    • Sebum: oily, waxy substance; low pH, high lipid content.
    • Sweat: low pH, high salt, and contains lysozyme (digests peptidoglycan).
    • Normal skin microbiome.

    Skin Normal Microbiota

    • Propionibacterium acnes
    • Staphylococci (e.g., Staphylococcus epidermidis, Staphylococcus aureus - in smaller numbers)
    • Streptococci species
    • Corynebacterium species
    • Peptostreptococcus species
    • Acinetobacter species
    • Small numbers of other species (e.g., Pseudomonas aeruginosa, Candida species).

    Streptococcus

    • Gram-positive cocci arranged in pairs or chains.
    • Most species are facultative anaerobes with complex nutritional requirements, needing blood or serum-enriched media for isolation.
    • Carbohydrate fermentation results in lactic acid production.
    • Catalase-negative streptococci.
    • Divided into groups (β-hemolytic, α-hemolytic, and γ-hemolytic) based on hemolysis patterns, classified by Lancefield grouping or biochemical testing.

    Streptococcus pyogenes

    • Streptococcus pyogenes is a rapidly growing gram-positive coccus arranged in chains.
    • Streptococcus pyogenes causes a variety of diseases, including pharyngitis, skin and soft-tissue infections, bacteremia, rheumatic fever, and acute glomerulonephritis.
    • Streptococcus pyogenes is commonly called "flesh-eating" bacteria due to its necrotic damage to muscle tissue.

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