Microbiology Quiz on Skin Infections
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Questions and Answers

Which of the following is NOT a bacterial skin infection?

  • Impetigo
  • Gas gangrene
  • Boils
  • Tinea (correct)

    • What factor increases the risk of fungal skin infections?

  • Wearing tight clothing
  • Consuming dairy products
  • Wearing sweaty or moist clothes (correct)
  • Exposure to sunlight

    • Which pathogen is primarily responsible for necrotizing fasciitis?

  • Streptococcus pyogenes (correct)
  • Clostridium perfringens
  • Staphylococcus aureus
  • Bacillus anthracis

    • What characteristic feature is associated with Staphylococcus aureus?

    <p>Gram-positive cocci in grape-like clusters</p> Signup and view all the answers

    Which of the following infections is MOST likely to be hospital-acquired due to antibiotic-resistant Staphylococci?

    <p>Hospital-acquired wound infections</p> Signup and view all the answers

    What mode of infection involves the direct introduction of a microbe into epithelium?

    <p>Surface penetration</p> Signup and view all the answers

    Which biochemical reaction is positive for Staphylococcus aureus?

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

    What is a common outcome of focal suppuration associated with Staphylococcus aureus?

    <p>Abscess formation</p> Signup and view all the answers

    What is the primary factor leading to the reactivation of the varicella-zoster virus?

    <p>Decreased cell-mediated immunity</p> Signup and view all the answers

    Which symptom is a characteristic of herpes zoster?

    <p>Severe unilateral pain</p> Signup and view all the answers

    Which mechanism primarily causes the maculopapular rash in measles?

    <p>Action of cytotoxic T cells</p> Signup and view all the answers

    What is the usual incubation period for measles?

    <p>10 days</p> Signup and view all the answers

    What type of infections are caused by HSV-1 in immunocompromised patients?

    <p>Disseminated infections like pneumonia</p> Signup and view all the answers

    What is the primary mode of transmission for rubella virus?

    <p>Airborne respiratory secretions</p> Signup and view all the answers

    What triggers recurrent infections of HSV-1?

    <p>Emotional stress and menstruation</p> Signup and view all the answers

    Which age is typically recommended for the first dose of the measles vaccination?

    <p>15 months</p> Signup and view all the answers

    What condition is most commonly associated with recurrent HSV-1 infections?

    <p>Herpes labialis</p> Signup and view all the answers

    How does chickenpox primarily spread among children?

    <p>Airborne transmission and contact with lesions</p> Signup and view all the answers

    What type of virus causes measles?

    <p>Negative-sense ssRNA virus</p> Signup and view all the answers

    What characterizes the rash of chickenpox?

    <p>All stages of the rash present at the same time</p> Signup and view all the answers

    What is the result of the initial infection with HSV-1?

    <p>Vesicular lesions heal without scarring and can recur</p> Signup and view all the answers

    What is a common post-infectious complication experienced by patients older than 65 years with herpes zoster?

    <p>Post herpetic neuralgia</p> Signup and view all the answers

    What is the incubation period for chickenpox?

    <p>14-21 days</p> Signup and view all the answers

    Which type of lesions does HSV-1 cause in normal individuals?

    <p>Vesicles that may change to ulcers but heal without scars</p> Signup and view all the answers

    What is a primary characteristic of Toxic Shock Syndrome (TSS)?

    <p>It can be caused by wound or localized infections.</p> Signup and view all the answers

    What is the main reason for Staphylococcus aureus' resistance to penicillin?

    <p>It produces b-lactamase, which destroys the b-lactam ring.</p> Signup and view all the answers

    Which toxin is associated with Scalded Skin Syndrome in infants?

    <p>Exfoliative toxins A and B</p> Signup and view all the answers

    What percentage of Staphylococcus aureus strains show resistance to methicillin?

    <p>20%</p> Signup and view all the answers

    What type of bacteria typically causes necrotizing fasciitis?

    <p>Streptococcus pyogenes</p> Signup and view all the answers

    Which of the following properties is true for Group A beta-hemolytic streptococci?

    <p>They produce beta hemolysis on blood agar.</p> Signup and view all the answers

    What is the function of pyrogenic exotoxin A from group A streptococci?

    <p>It serves as a superantigen causing cytokine release.</p> Signup and view all the answers

    Which of the following statements is true regarding Staphylococcus aureus and antibiotic resistance?

    <p>Some strains show complete resistance to methicillin.</p> Signup and view all the answers

    What is the main cause of acute bacterial endocarditis related to Str. pyogenes?

    <p>Deformed heart valves</p> Signup and view all the answers

    What characterizes the skin infection known as erysipelas?

    <p>Redness and edema with advancing margins</p> Signup and view all the answers

    Which of the following is a possible outcome of pyoderma?

    <p>Acute glomerulonephritis</p> Signup and view all the answers

    What is a common consequence of invasive diseases caused by Str. pyogenes?

    <p>Streptococcal septicaemia</p> Signup and view all the answers

    Which strain of streptococcus is primarily associated with streptococcus toxic shock syndrome?

    <p>M type 1, 3, 12 &amp; 28</p> Signup and view all the answers

    What symptom is commonly associated with scarlet fever?

    <p>Sore throat with an erythematous rash</p> Signup and view all the answers

    What shows a common laboratory finding in acute glomerulonephritis?

    <p>Presence of granular casts in urine</p> Signup and view all the answers

    What is the primary effect of alpha toxin from Clostridium perfringens?

    <p>Increases vascular permeability and causes tissue destruction</p> Signup and view all the answers

    What is necrotizing fasciitis primarily characterized by?

    <p>Destruction of fascia and fat</p> Signup and view all the answers

    Which toxin produced by Clostridium perfringens is associated with necrotizing lesions in the intestinal tract?

    <p>Theta toxin</p> Signup and view all the answers

    What method is used to diagnose superficial mycosis caused by Malassezia furfur?

    <p>KOH mount of skin scales</p> Signup and view all the answers

    What are the clinical manifestations of superficial mycosis primarily characterized by?

    <p>Cosmetic symptoms such as hypo- or hyperpigmented skin patches</p> Signup and view all the answers

    Which species of dermatophyte is NOT mentioned as a common cause of cutaneous mycosis?

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

    What is the purpose of adding chloramphenicol to Sabouraud's dextrose agar?

    <p>To inhibit bacterial contaminants</p> Signup and view all the answers

    What is a characteristic feature of subcutaneous mycosis, such as Madura foot?

    <p>Swelling and abscess formation with drainage through sinus tracts</p> Signup and view all the answers

    Which enzyme is NOT produced by Clostridium perfringens as an extracellular enzyme?

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

    Signup and view all the answers

    Study Notes

    MUSKULOSKELETAL BLOCK

    • Skin and soft tissue infections are caused by various germs, symptoms vary from mild to severe.
    • Minor trauma damages the integrity of the skin, allowing microbes to enter.
    • Surface openings like hair follicles and sebaceous glands are entry points for microbes.
    • Wearing sweaty or moist clothes increases the risk of fungal infections.
    • Infection severity is graded according to anatomical depth.

    MODES OF INFECTION

    • Direct entry of microbes into epithelial tissue.
    • Circulating microbes.
    • Circulating toxins.

    TYPES OF SKIN INFECTIONS

    • Bacterial infections: Boils (Staphylococcus aureus), Impetigo (Streptococcus pyogenes & Staphylococcus aureus), Cellulitis (Streptococcus pyogenes), Necrotizing fasciitis (Streptococcus pyogenes), Anthrax (Bacillus anthracis), Gas gangrene (Clostridium perfringens), Burn infection (Pseudomonas), Leprosy (Mycobacterium leprae).
    • Fungal infections
    • Viral infections

    STAPHYLOCOCCUS AUREUS

    • Natural Habitat: Nostrils, skin
    • Morphology: Gram-positive cocci (grape-like clusters), non-motile, non-encapsulated, non-spore forming.
    • The most common cause of localized suppurative lesions in humans.
    • Specific symptoms include boils, cellulitis, impetigo, and paronychia.

    CULTURAL CHARACTERISTICS

    • Facultative anaerobic bacteria.
    • Grow on nutrient and blood agar, forming large, yellow to creamy colonies.
    • Often hemolytic on blood agar.
    • Mannitol salt agar is a selective medium.
    • Grows at 15-45°C and high NaCl concentrations.

    BIOCHEMICAL REACTIONS

    • Catalase: Positive
    • Coagulase: Positive
    • DNase: Positive
    • Oxidase: Negative
    • Ferments glucose, lactose, sucrose, mannitol to produce acid.

    VIRULENCE FACTORS OF S. AEREUS

    • Structural Components:

      • Protein A: major cell wall protein, disrupts immune defenses, binds to Fc region of IgG, disrupts phagocytosis
      • Polysaccharide Capsule: Antiphagocytic, facilitates attachment to foreign bodies

    • Enzymes:

      • Coagulase: coagulates plasma and blood, diagnostic
      • Hyaluronidase: degrades connective tissue
      • Staphylokinase: digests blood clots
      • DNase: digests DNA
      • Lipases: digest oils, enhance colonization
      • Penicillinase: inactivates penicillin

    • Toxins:

      • Hemolysins (alpha, beta, gamma, delta): lyse red blood cells
      • Leukocidin: lyses leukocytes (neutrophils and macrophages).
      • Enterotoxin: causes gastrointestinal distress.
      • Exfoliative toxin: separates epidermis from dermis
      • Toxic shock syndrome toxin (TSST): induces fever, vomiting, shock, and organ damage.

    DISEASES CAUSED BY S. AUREUS

    • Focal suppuration and abscess formation
    • Superficial infections (e.g., folliculitis, carbuncles, boils)
    • Deep-seated lesions (e.g., osteomyelitis, bronchopneumonia, empyema, endocarditis, meningitis).
    • Bacteremia with multiple abscesses.
    • Hospital-acquired wound infections.
    • Septicemia (sepsis)
    • Toxigenic diseases (e.g., toxic shock syndrome, scaled skin syndrome).

    STREPTOCOCCUS PYOGENES

    • Morphology: Gram-positive cocci in chains, non-motile, non-spore forming.
    • Group A beta-hemolytic streptococci.
    • Catalase-negative
    • Pathogenesis: adhesion, invasion, escape from phagocytes, enzyme and toxin production.

    VIRULENCE FACTORS OF S. PYOGENES

    • Structural Components:

      • M protein: binds the complement, prevents phagocytosis and opsonization.
      • Lipoteichoic acid and F protein: adhesion and invasion.
      • Hyaluronic acid capsule: camouflage and acts as a defense mechanism.

    • Enzymes: -Streptokinase: digests blood clots -Deoxynucleases: degrade DNA -C5a peptidase: inhibits complement activation

    • Pyrogenic toxins: contribute to various diseases.

    DISEASES CAUSED BY S. PYOGENES

    • Pyogenic local infections (e.g., pyoderma, erysipelas)
    • Invasive diseases (e.g., streptococcal toxic shock syndrome)
    • Post-streptococcal immunologic diseases (e.g., acute glomerulonephritis)

    BACILLUS ANTHRACIS

    • Morphology: Gram-positive, rectangular, large organisms in chains, encapsulated in vivo. Capsulated cells stain pink when viewed in certain dyes.
    • Aerobic bacteria, can grow on nutrient agar at 37°C
    • Virulence factors: polypeptide capsule, toxin production (antiphagocytic).
    • Pathogenesis: capsule and toxin (anthrax toxin -made up of 3 fractions:Edema factor (EF), Protective antigen (PA), Lethal factor (LF)).

    PSEUDOMONAS AERUGINOSA

    • Morphology: Gram-negative bacilli, non-spore forming, non-capsulated, motile by polar flagella.
    • Obligate aerobic.
    • Can grow on simple media, with sweet grape odor, causing greenish discoloration.
    • Contains pyocyanin (blue) and pyoverdin (greenish yellow) pigments.
    • Oxidase-positive.

    CLOSTRIDIUM PERFRINGENS

    • Morphology: Large Gram-positive bacilli, non-motile, encapsulated, and have central or subterminal spores
    • Anaerobic
    • Pathogenesis: produce toxins after sporulation, various toxins include alpha toxin, theta toxin, and enterotoxin.

    PATHOGENESIS OF C. PERFRINGENS

    • Spores germinate, vegetative cells multiply and ferment carbohydrates, resulting in tissue distension, interference
    • Hemolytic and toxic effects
    • Associated diseases include soft tissue infection (cellulitis, fasciitis, myonecrosis (gas gangrene)) and food poisoning

    FUNGAL SKIN INFECTIONS

    • Superficial mycoses (e.g., tinea versicolor)
    • Cutaneous mycoses (e.g., ringworm)
    • Subcutaneous mycoses (e.g., madura foot)
    • Sporotrichosis (e.g., from thorns)
    • Candidiasis (e.g., yeast-like fungus)

    VIRAL SKIN INFECTIONS

    • Herpes simplex type 1: oral or genital cold sores
    • Chickenpox(varicella): highly contagious
    • Shingles (Herpes zoster): reactivation of latent virus, characteristic pain and rash
    • Rubella(German Measles): airborne transmission.
    • Measles: airborne transmission
    • Hand-foot-and-mouth disease: Viral infection mostly affecting children, common symptoms include fever, sores in mouth, sores or rash on hands/feet/buttocks.
    • Genital warts(human papillomavirus): common in children/immunocompromised individuals, sexually transmitted

    CANDIDIASIS

    • Candida albicans is a common species
    • Extremes of age, chronic debilitating diseases, diabetes mellitus, malnutrition, excessive moisture, pregnancy, and long-term antibiotic or steroid use predispose to infections.
    • Skin lesion signs include areas of red itchy skin, or inflammation of the nails/skin folds/groin regions.

    MOLLUSCUM CONTAGIOSUM

    • Benign skin nodules, usually on arms, face, and genitals.
    • Virus is transmitted through close contact and sexually
    • Common in children and immunocompromised individuals.

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