Microbiology Quiz on Staphylococcus aureus
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Questions and Answers

What is the primary mechanism by which aureus causes diseases such as toxic shock syndrome and staphylococcal food poisoning?

  • Formation of granulomas
  • Production of toxins (correct)
  • Direct invasion and destruction of tissue
  • Proliferation of bacteria leading to abscess formation

    • Which disease results from the activity of exfoliative toxins produced by aureus?

  • Pneumonia
  • Osteomyelitis
  • Staphylococcal Scalded Skin Syndrome (SSSS) (correct)
  • Endocarditis

    • What is a key characteristic that differentiates bullous impetigo from Staphylococcal Scalded Skin Syndrome (SSSS)?

  • Bullous impetigo occurs only in infants
  • SSSS involves localized infections only
  • Bullous impetigo is associated with the presence of bacteria and leukocytes (correct)
  • SSSS is always more severe than bullous impetigo

    • What defines the stability of staphylococcal enterotoxins in terms of temperature and digestive enzymes?

    <p>Stable at 100°C for 30 minutes and resistant to gastric enzymes (B)</p> Signup and view all the answers

    What is a common outcome associated with diseases caused by the proliferation of aureus bacteria?

    <p>Formation of abscesses and tissue destruction (A)</p> Signup and view all the answers

    Which statement accurately describes the characteristics of Staphylococcus species?

    <p>Staphylococcus species are non-motile and do not produce spores. (A)</p> Signup and view all the answers

    What feature distinguishes Staphylococcus aureus from other staphylococcal species?

    <p>It produces coagulase. (D)</p> Signup and view all the answers

    How does Staphylococcus aureus primarily resist phagocytosis?

    <p>By utilizing its polysaccharide capsule. (B)</p> Signup and view all the answers

    What is the primary reservoir for Staphylococcus aureus in the human population?

    <p>Healthy individuals on their skin and nasopharynx. (C)</p> Signup and view all the answers

    What is the primary cause of death in patients with Toxic Shock Syndrome (TSS)?

    <p>Hypovolemic shock leading to multiorgan failure (D)</p> Signup and view all the answers

    Which of the following statements about the growth conditions of Staphylococcus aureus is true?

    <p>It can grow in both aerobic and anaerobic conditions. (B)</p> Signup and view all the answers

    What is the primary role of Protein A in Staphylococcus aureus?

    <p>To bind to the Fc region of IgGs and prevent antibody production. (C)</p> Signup and view all the answers

    Which method is considered the gold standard for the laboratory diagnosis of Staphylococcus aureus?

    <p>Microscopic examination and culture on agar plate (A)</p> Signup and view all the answers

    What characteristic of S.aureus allows it to be selectively isolated on mannitol-salt agar?

    <p>Fermentation of mannitol (B)</p> Signup and view all the answers

    What feature of Staphylococcus aureus colonies can be visually identified as a distinguishing characteristic?

    <p>Yellow or gold color due to carotenoid pigments. (C)</p> Signup and view all the answers

    Which condition is primarily associated with the presence of Large skin lesions and peeling?

    <p>Toxic Shock Syndrome (B)</p> Signup and view all the answers

    What is the primary function of MSCRAMM proteins in Staphylococcus aureus?

    <p>To facilitate adhesion to host tissues. (B)</p> Signup and view all the answers

    What is a typical symptom of septic arthritis?

    <p>Collection of purulent material in the joint space (D)</p> Signup and view all the answers

    Which test is specifically used for biochemical identification of S.aureus?

    <p>Coagulase test (B)</p> Signup and view all the answers

    What combination of antibiotics is commonly used for empirical treatment of serious pneumococcal infections?

    <p>Vancomycin and ceftriaxone (D)</p> Signup and view all the answers

    Which of the following conditions is associated with the destruction of bones?

    <p>Osteomyelitis (A)</p> Signup and view all the answers

    What is a characteristic of MRSA strains?

    <p>Resistance to methicillin and related penicillins (D)</p> Signup and view all the answers

    Which of the following is a recommended vaccine for infants younger than 2 years?

    <p>13-valent conjugated pneumococcal vaccine (C)</p> Signup and view all the answers

    What is the primary reason enterococci are considered nosocomial pathogens?

    <p>They are associated with urinary catheterization or instrumentation (A)</p> Signup and view all the answers

    What characteristic can be observed in Bile Esculin agar when enterococci are present?

    <p>Blackening of the medium (A)</p> Signup and view all the answers

    Which of the following antibiotics is known to have a resistance issue with Streptococcus pneumoniae?

    <p>Amoxicillin (A)</p> Signup and view all the answers

    What characterizes early-onset disease caused by Streptococcus agalactiae?

    <p>Sepsis and pneumonia within the first 7 days of life (B)</p> Signup and view all the answers

    At what gestational weeks should pregnant women be screened for Streptococcus agalactiae?

    <p>35 to 37 weeks (B)</p> Signup and view all the answers

    What is the major protective antigen of Streptococcus pneumoniae?

    <p>Polysaccharide capsule (C)</p> Signup and view all the answers

    Which of the following infections can be caused by Streptococcus pneumoniae?

    <p>Pneumonia and meningitis (C)</p> Signup and view all the answers

    What indicates the autolysis process of Streptococcus pneumoniae colonies on agar?

    <p>The central portion of the colony dissolves, leaving a depression (B)</p> Signup and view all the answers

    Which of the following describes the Gram-staining characteristics of Streptococcus pneumoniae?

    <p>Gram-positive cocci, arranged in pairs (A)</p> Signup and view all the answers

    What complications may arise in adult patients infected with Streptococcus agalactiae?

    <p>Endocarditis and urinary tract infections (C)</p> Signup and view all the answers

    Which of the following statements is true regarding the teichoic acids in Streptococcus pneumoniae?

    <p>One form precipitates C-reactive protein (C)</p> Signup and view all the answers

    What is the primary purpose of IgA-protease in the context of colonization by S.pneumoniae?

    <p>To destroy secretory IgA produced in the mucosa (A)</p> Signup and view all the answers

    Which of the following correctly describes the method of transmission of S.pneumoniae?

    <p>From asymptomatic carriers through aerosols (B)</p> Signup and view all the answers

    What is a distinguishing feature of pneumococcal pneumonia onset?

    <p>Abrupt onset with severe shaking chill and high fever (D)</p> Signup and view all the answers

    In which bodily fluid would you expect to find pneumococcal antigens during disease detection?

    <p>Cerebrospinal fluid (CSF) (C)</p> Signup and view all the answers

    Which type of sample is most commonly used for culture to detect S.pneumoniae?

    <p>Sputum and blood (D)</p> Signup and view all the answers

    What is the significance of pneumolysin in S.pneumoniae infection?

    <p>It forms pores in membranes and aids in bacterial replication and dissemination (C)</p> Signup and view all the answers

    What percentage of patients surviving pneumococcal meningitis may experience neurological sequelae?

    <p>30 to 52% (B)</p> Signup and view all the answers

    What laboratory test can directly identify S.pneumoniae from cerebrospinal fluid?

    <p>PCR assays (B)</p> Signup and view all the answers

    Flashcards

    Staphylococcus aureus

    A type of bacteria that can cause disease through the production of toxins or by directly invading and destroying tissue.

    Staphylococcal Scalded Skin Syndrome (SSSS)

    A staphylococcal disease caused by the production of toxins that lead to the peeling of skin.

    Bullous Impetigo

    Localized form of Staphylococcal Scalded Skin Syndrome (SSSS) characterized by blisters on a red base.

    Staphylococcal Enterotoxins

    Toxins produced by Staphylococcus aureus that cause food poisoning.

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    Suppurative Infections

    Infections caused by the proliferation of bacteria, leading to the formation of pus-filled pockets called abscesses.

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    Staphylococcus

    A genus of Gram-positive bacteria belonging to the Staphylococcaceae family, known for its spherical shape and arrangement in clusters.

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    Coagulase-negative Staphylococci (CoNS)

    A group of Staphylococcus species other than S. aureus that do not produce coagulase.

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    MSCRAMM proteins (Microbial Surface Components Recognizing Adhesive Matrix Molecules)

    Proteins on the surface of bacteria that allow them to attach to host cells and tissues.

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    Polysaccharide Capsule

    A layer of polysaccharide that surrounds some bacteria, protecting them from the host's immune system by inhibiting phagocytosis.

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    Protein A

    A protein produced by S. aureus that binds to the Fc region of IgG antibodies, blocking their ability to activate the immune system.

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    S. aureus Secreted Proteins

    Enzymes and toxins produced by S. aureus that contribute to its virulence and ability to cause disease.

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    Cytotoxins of S. aureus

    Toxins produced by S. aureus that damage host cells, leading to tissue destruction and inflammation.

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    Toxic Shock Syndrome (TSS)

    Staphylococcus aureus can multiply rapidly in tampons and release toxin, leading to a potentially life-threatening condition known as Toxic Shock Syndrome (TSS).

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    TSS: Causes and Symptoms

    Toxic Shock Syndrome (TSS) is often associated with the use of tampons, but it can also be caused by wounds. It is characterized by a sudden onset of high fever, low blood pressure, and a widespread rash.

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    TSS: Complications

    TSS can lead to multi-organ failure and death due to hypovolemic shock, which is a condition where the body loses a significant amount of blood volume.

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    Furuncles (Boils)

    Furuncles, commonly known as boils, are painful, pus-filled nodules that develop on the skin.

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    Carbuncles

    Carbuncles are a more severe form of furuncles where multiple boils coalesce and extend into the subcutaneous tissues.

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    Osteomyelitis

    Osteomyelitis is an infection that affects the bone. It causes inflammation and destruction of the bone tissue.

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    Septic Arthritis

    Septic arthritis is an infection of a joint. It causes pain, redness, and swelling in the affected joint, along with the accumulation of pus within the joint space.

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    S. aureus and Bacteremia/Endocarditis

    Staphylococcus aureus is a common cause of bacteremia (bacteria in the blood) and endocarditis (inflammation of the heart's inner lining).

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    Streptococcus agalactiae (Group B Strep)

    A type of bacteria that can cause serious infections such as sepsis, pneumonia, and meningitis in newborns.

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    Early-onset Neonatal Streptococcus agalactiae Infection

    A type of infection caused by Streptococcus agalactiae that occurs within the first 7 days of life; often involves sepsis and pneumonia.

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    Late-onset Neonatal Streptococcus agalactiae Infection

    A type of infection caused by Streptococcus agalactiae that occurs between 7 days and 3 months of age; often involves meningitis and sepsis.

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    Streptococcus pneumoniae

    A type of bacteria that can cause infections like pneumonia, sinusitis, and otitis media.

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    Phosphorylcholine

    A cell wall component of Streptococcus pneumoniae that plays a role in its ability to cause disease and evade the immune system.

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    Hemolysis

    The ability of a bacterium to produce a clear zone around its colony on a blood agar plate due to the breakdown of red blood cells.

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    Alpha-hemolysis

    A type of hemolysis characterized by a greenish discoloration around bacterial colonies on a blood agar plate.

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    Colonization

    The process by which a bacterium, such as S. pneumoniae, establishes itself in the respiratory tract.

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    Surface protein adhesins

    Specialized proteins that allow S. pneumoniae to attach to the cells lining the nasopharynx.

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    IgA-protease

    An enzyme produced by S. pneumoniae that breaks down IgA antibodies, which help protect the body from infections.

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    Pneumolysin

    A toxin produced by S. pneumoniae that creates holes in cell membranes, leading to cell death.

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    Pneumococcal pneumonia

    The spread of S. pneumoniae from the nasopharynx to the lungs, causing pneumonia.

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    Pneumococcal meningitis

    An infection of the brain and spinal cord caused by S. pneumoniae.

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    Gram staining

    A test that uses microscopy to identify S. pneumoniae by its characteristic appearance.

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    13-valent conjugated pneumococcal vaccine

    A vaccine recommended for infants under 2 years old, protecting them from severe pneumococcal infections like pneumonia and meningitis. It consists of 13 different pneumococcal strains.

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    23-valent pneumococcal polysaccharide vaccine

    A vaccine recommended for children over 2 years old and adults. It helps protect against pneumococcal infections, but it's less effective than the 13-valent vaccine.

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    Enterococcus

    A genus of bacteria commonly found in the gut of humans and animals. They can cause infections, particularly in hospital settings.

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    Bile Esculin agar

    A selective and differential culture medium used to identify enterococci. The bacteria hydrolyze esculin, leading to the blackening of the medium.

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    Study Notes

    Gram Positive Cocci

    • Staphylococcus, Streptococcus, Enterococcus are gram-positive cocci.

    Staphylococcus spp.

    • Staphylococcus is a genus of gram-positive bacteria in the Staphylococcaceae family, currently with 49 species.
    • Gram-positive cocci, about 1 µm in diameter, arranged in clusters.
    • Do not produce spores, are non-motile, and produce exotoxins.
    • Ubiquitous in animals and humans.
    • Survive for long periods on dry surfaces.
    • Examples of Staphylococcus species: aureus, epidermidis, saprophyticus, haemolyticus, lugdunensis.

    Staphylococcus aureus

    • S. aureus colonies can be yellow or gold, resulting from carotenoid pigments produced during growth.
    • Produces coagulase, which differentiates it from other coagulase-negative staphylococci (CoNS).
    • CoNS are a group of staphylococcal species that don't produce coagulase.

    Epidemiology of S. aureus

    • Humans are reservoirs for S. aureus, with 15-50% of healthy individuals carrying it.
    • Colonizes the skin and nasopharynx, capable of transmission via direct contact or fomites (e.g., contaminated items).

    S. aureus Virulence Factors

    • Adhesins: Bind to host tissue receptors, host cells, and soluble factors to inhibit complement cascade.
    • Autolysins: Highly immunogenic cell wall transglycosylases that facilitate non-professional phagocyte invasion.
    • Leukocidins: Secreted toxins and peptides targeting and killing key host immune cells.
    • Immunoglobulin Binding Proteins: Bind IgGs via Fc regions, inhibit host immune factors.
    • Capsule: Protects the bacteria from phagocytosis, preventing destruction.
    • MSCRAMM proteins: Adhere to host matrix proteins like fibronectin and collagen.
    • Protein A: Binds to Fc regions of IgGs, preventing phagocytosis and decreasing the production of S. aureus-specific antibodies.
    • Superantigens: Are potent stimulatory exotoxins that trigger cytokine release by activating T-cells.

    S. aureus: Secreted Proteins

    • Coagulase: Converts fibrinogen to fibrin.
    • Hyaluronidase: Breaks down hyaluronic acid, promoting bacterial spread in connective tissue.
    • Fibrinolysin: Dissolves fibrin clots.
    • Lipases: Hydrolyze lipids.
    • Nucleases: Hydrolyze DNA.
    • Cytotoxins: Toxic to various cells like erythrocytes, fibroblasts, leukocytes, macrophages, and platelets.
    • Exfoliative Toxins (ETA, ETB): Serine proteases that split intercellular bridges in the stratum granulosum epidermis, causing skin exfoliation.
    • Enterotoxins (A-E, G-I): Superantigens stimulating T-cell proliferation causing inflammatory mediators release and affecting intestinal peristalsis and fluid loss.
    • Toxic shock syndrome toxin-1 (TSST-1): Superantigen triggering cytokine release, and causing endothelial cell leakage.

    Staphylococcus aureus: Clinical Diseases

    • Staphylococcal scalded skin syndrome (SSSS): Mediated by exfoliative toxins that split desmoglein-1, leading to disseminated desquamation of the epithelium, typically in infants.
    • Bullous impetigo: Localized cutaneous infection characterized by vesicles on a erythematous base.
    • Other infections: Includes suppurative infections like furuncles/boils, carbuncles, osteomyelitis, septic arthritis, endocarditis.

    Enterotoxins and Food Poisoning

    • Numerous staphylococcal enterotoxins exist, stable to heat (100°C for 30 minutes) and gastric hydrolysis.
    • Contamination with enterotoxin-producing staphylococci can cause rapid onset vomiting, diarrhea, and abdominal cramps, resolving within ~24 hours.
    • Common contaminated foods include processed meats, ham, salted pork, and custard-filled pastries.

    Staphylococcal Enterotoxins (SE)

    • Table showing the molecular weight, genetic basis (prophage, chromosome, plasmid, pathogenicity island), superantigenic activity, and emetic activity of various SEs.

    Toxic Shock Syndrome Toxin-1 (TSST-1)

    • TSST-1-producing strains live in the vagina of infected women, causing systemic effects of toxic shock syndrome (like hypotension and shock) after penetrating the mucosal barriers.

    Toxic Shock Syndrome (TSS)

    • Initial reports in menstruating women in 1980's, but it also occurs in men and is associated with wounds.
    • Associated with hypovolemic shock leading to multiorgan failure.
    • Characterized by fever, hypotension, diffuse peeling, and large skin lesions.

    Coagulase-negative Staphylococci (CoNS)

    • Common bacteria on the human skin and also associated with prosthetic heart valves and native heart valves (endocarditis) and shunt and catheter infections, including intravascular catheter-associated infections.
    • Staphylococcus epidermidis, Staphylococcus saprophyticus, Staphylococcus haemolyticus, and Staphylococcus lugdunensis are examples.

    Staphylococcus epidermidis

    • Gram-positive, aero-anaerobic facultative, clustered.
    • Optimal growth temp = 30-37°C.
    • Found in stratum corneum, epidermal basement membrane, sebaceous regions.
    • Colonizes the skin via sebaceous/oily lipids, sebum, anaerobic follicles, and low pH.

    Streptococcus spp.

    • Streptococcus is a genus of gram-positive bacteria in the Streptococcaceae family.
    • Gram-positive cocci in pairs or chains.
    • Fastidious growth requirements; facultative anaerobes; negative catalase.

    Streptococcus pyogenes

    • Gram-positive cocci, beta-hemolytic bacteria, Lancefield group A.
    • Produces toxins like streptolysin S (oxygen-stable) and O (oxygen-labile).
    • Associated with pharyngitis, scarlet fever, impetigo, erysipelas, toxic shock syndrome, necrotizing fasciitis, and acute glomerulonephritis.

    Streptococcal pyrogenic exotoxins (SPEs)

    • SPEs are heat-labile superantigens that stimulate macrophage and T-cell cytokines release.

    Streptokinase

    • Enzyme that dissolves blood clots and fibrin deposits to spread initial infection site.
    • Encoded by phages.
    • DNases (A-to-D) depolymerize deoxyribonucleic acid in infectious sites, reducing environmental viscosity.
    • Hyaluronidase hydrolyzes hyaluronic acid
    • C5-peptidase inhibits complement system.

    Streptococcus agalactiae

    • Gram-positive cocci, beta-hemolytic bacteria, Lancefield group B.
    • Virulence factor is a large polysaccharide capsule.
    • Causes neonatal infections (early and late-onset)
    • Associated with significant mortality rates in newborns.
    • Colonisation of mother's vagina/rectum.
    • Preventable through antibiotic prophylaxis (IV penicillin G or ampicillin) for colonized women before delivery.

    Streptococcus pneumoniae

    • Gram-positive cocci, alpha and beta hemolytic, doesn't have a Lancefield group.
    • Encapsulated diplococci, but also non-encapsulated smaller and flatter colonies on blood agar.
    • Autolysis and aging leads to colony depression.
    • Major antiphagocytic surface element and protective antigen is its capsule polysaccharide.
    • Causes pneumonia, sinusitis, otitis media (middle ear infection), and meningitis.
    • Frequently transmitted via aerosol from asymptomatic carriers or those displaying active disease.
    • Susceptible to antibiotic optochin.
    • Diagnosis involves gram staining, sputum and CSF detection, PCR testing blood cultures.
    • Treatment may include empiric use of antibiotic combination therapies.

    Laboratory Diagnosis

    • Microscopy and staining: Observing Gram-positive cocci (pairs or clusters) in biological samples like throats swabs, purulent materials, CSF, blood.
    • Culture: Gold standard for identifying S. pyogenes, involves bacterial growth on blood agar plates, observing beta-hemolytic colonies. Bacitracin susceptibility test differentiates between S. pyogenes and S. agalactiae.
    • Antibody detection: Detecting antibodies against streptolysin O (ASO test) for confirming rheumatic fever or acute glomerulonephritis.

    Treatment

    • Staphylococcal infections may be treated with penicillin, amoxicillin, cephalosporins or macrolides according to penicillin allergies.
    • Streptococcus pneumoniae infections, given resistance to penicillin (50% strains), requiring combinations of antibiotics (e.g., vancomycin combined with ceftriaxone), followed by cephalosporins, fluoroquinolones, or vancomycin monotherapy.
    • Long-term antibiotic prophylaxis with IM penicillin G can prevent recurrence in patients with a history of rheumatic fever.

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    Description

    Test your knowledge on the pathogenic mechanisms and characteristics of Staphylococcus aureus. This quiz covers diseases such as toxic shock syndrome and bullous impetigo, and explores the stability and resistance of this bacteria. Perfect for microbiology students seeking to deepen their understanding of this important pathogen.

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