Staphylococci and Diagnostic Tests
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Questions and Answers

Which test is used to differentiate Staphylococcus aureus from other staphylococci?

  • Oxidase test
  • Catalase test
  • Coagulase test (correct)
  • Gram stain

    • What does the presence of catalase indicate when testing bacteria?

  • The bacteria can reduce hydrogen peroxide (correct)
  • The bacteria are fermenters
  • The bacteria are spore-forming
  • The bacteria are Gram-negative

    • Which of the following best describes a painful, red lump on the neck?

  • Cold sore
  • Furuncle (correct)
  • Wart
  • Acne

    • Which species of staphylococci is most likely to cause skin infections in healthy individuals?

    <p>Staphylococcus aureus</p> Signup and view all the answers

    What type of infection is indicated by the presence of a painful lump that forms due to a skin infection?

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

    Is further management required for a simple furuncle?

    <p>No, it resolves on its own</p> Signup and view all the answers

    Which factor increases the likelihood of colonization by Staphylococcus aureus?

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

    What enzyme produced by Staphylococcus aureus helps it resist phagocytosis?

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

    What is the role of the clumping factor in S. aureus?

    <p>Promotes attachment to blood clots</p> Signup and view all the answers

    Which of the following best describes invasin production in S. aureus?

    <p>Promotes bacterial invasion</p> Signup and view all the answers

    What kind of damage does peptidoglycan wall cause in host cells?

    <p>Direct damage to host cell structures</p> Signup and view all the answers

    Which condition is associated with the exfoliative toxins produced by S. aureus?

    <p>Scalded Skin Syndrome</p> Signup and view all the answers

    What type of infection is primarily caused by toxic shock syndrome toxin (TSST-1)?

    <p>Systemic infections</p> Signup and view all the answers

    How does S. aureus typically spread between individuals?

    <p>Through direct skin contact</p> Signup and view all the answers

    Which of the following is a characteristic of food poisoning caused by S. aureus?

    <p>Self-limiting nature</p> Signup and view all the answers

    What is a common systemic infection caused by S. aureus that often follows a bloodstream infection?

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

    What type of bacteria are staphylococci classified as?

    <p>Gram-positive bacteria</p> Signup and view all the answers

    How do staphylococci appear under a microscope?

    <p>Spherical and in clusters</p> Signup and view all the answers

    Which species of staphylococci is known for its ability to clot blood plasma?

    <p>Staphylococcus aureus</p> Signup and view all the answers

    What characteristic allows staphylococci to be classified as facultative anaerobes?

    <p>They can grow in both the presence and absence of oxygen.</p> Signup and view all the answers

    Which of the following locations can Staphylococcus aureus colonize?

    <p>Moist skin areas like the axilla and groin</p> Signup and view all the answers

    What is the primary focus of the learning outcomes for the course on staphylococci?

    <p>Understanding basic laboratory features and pathology of staphylococci</p> Signup and view all the answers

    What are some clinical features associated with infections caused by staphylococci?

    <p>Skin lesions and abscesses</p> Signup and view all the answers

    Which of these is an approach to prevent the spread of staphylococcal infections?

    <p>Regular hand washing and hygiene measures</p> Signup and view all the answers

    What is the function of coagulase produced by Staphylococcus aureus?

    <p>Converts fibrinogen to fibrin</p> Signup and view all the answers

    Which characteristic differentiates staphylococci from streptococci during laboratory testing?

    <p>Catalase activity</p> Signup and view all the answers

    What is the primary portal of entry for Staphylococcus aureus infections?

    <p>Break in the skin</p> Signup and view all the answers

    Which demographic is at an increased risk for Staphylococcus aureus infections?

    <p>Elderly patients in healthcare settings</p> Signup and view all the answers

    Which condition typically indicates an endogenous infection?

    <p>Skin infection caused by a cut</p> Signup and view all the answers

    What type of precautions should be taken in a healthcare setting for patients colonized with MRSA?

    <p>Isolation and contact precautions</p> Signup and view all the answers

    What happens in the catalase test when catalase is present in bacteria?

    <p>Bubbles produced from hydrogen peroxide</p> Signup and view all the answers

    Which of the following species is associated with lower virulence and typically colonizes the skin?

    <p>Staphylococcus epidermidis</p> Signup and view all the answers

    What type of enzymes does S. aureus produce to promote invasion?

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

    Which symptom is characteristic of Toxic Shock Syndrome caused by S. aureus?

    <p>High fever and rash</p> Signup and view all the answers

    What mechanism does S. aureus use to evade the immune system?

    <p>Inhibition of phagocytosis</p> Signup and view all the answers

    What type of infection can result from S. aureus's ability to spread on surfaces?

    <p>Food poisoning</p> Signup and view all the answers

    How is Scalded Skin Syndrome primarily caused by S. aureus?

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

    What is the primary outcome of peptidoglycan damage to host cells?

    <p>Cell lysis</p> Signup and view all the answers

    Which of the following is a common systemic infection associated with S. aureus?

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

    What is a common route for person-to-person transmission of S. aureus?

    <p>Direct skin contact</p> Signup and view all the answers

    Which feature is characteristic of Staphylococcus bacteria?

    <p>They form in clusters.</p> Signup and view all the answers

    What primarily differentiates coagulase-positive staphylococci from coagulase-negative staphylococci?

    <p>Their reaction to the coagulase test.</p> Signup and view all the answers

    Which of the following staphylococci is known for its potential to cause skin infections in humans?

    <p>Staphylococcus aureus</p> Signup and view all the answers

    What is the primary mode of action for antimicrobial agents used to treat staphylococcal infections?

    <p>Disrupting cell wall synthesis.</p> Signup and view all the answers

    Which clinical feature is typically associated with infections caused by staphylococci?

    <p>Characteristic rashes and pustules.</p> Signup and view all the answers

    What preventive measure is recommended to avoid the spread of staphylococcal infections?

    <p>Regular hand hygiene.</p> Signup and view all the answers

    Which bacterium is often part of the normal human flora but can become pathogenic under certain conditions?

    <p>Staphylococcus epidermidis</p> Signup and view all the answers

    Which characteristic allows staphylococci to survive in various environments?

    <p>Their facultative anaerobic metabolism.</p> Signup and view all the answers

    Study Notes

    Staphylococci

    • Staphylococci are a genus of Gram-positive bacteria
    • They are spherical (cocci) and form in clumps/clusters
    • They are facultative anaerobes
    • Traditionally divided into two groups based on their ability to clot blood plasma (coagulase reaction/test)
      • Coagulase-positive staphylococci (e.g., S. aureus):
        • Colonize nasal passages and moist skin areas (axilla, groin)
      • Coagulase-negative staphylococci (>30 other species):
        • Common human skin commensals (e.g., S. epidermidis)

    Coagulase Test

    • A laboratory test used to differentiate S. aureus from other staphylococci (negative)
    • Coagulase is an enzyme that causes blood clot formation (converting fibrinogen to fibrin)
    • Allows bacteria to coat its surface with fibrin, potentially resisting phagocytosis

    Catalase Test

    • Used to differentiate staphylococci from streptococci (also a Gram-positive coccus)
    • Presence of catalase (enzyme) is determined by the bacteria's ability to reduce hydrogen peroxide into water and oxygen, resulting in bubble production
    • Staphylococci = Catalase +

    Clinical Case 1

    • A 19-year-old male presents with a painful, red lump on his neck
    • The most likely diagnosis is a furuncle

    Staphylococcus aureus (S. aureus)

    • Found in moist skin folds, mucosal surfaces, nasopharynx
    • 20–40% of healthy humans are colonized
    • Increased colonization in individuals with diabetes mellitus, injecting drug use, or foreign bodies/implants
    • Distinguished as methicillin-sensitive (MSSA) or methicillin-resistant (MRSA)
      • Resistance to usual treatments results from an alteration of penicillin-binding protein (PBP2a)
      • Usually a healthcare-associated infection; elderly and those with compromised immune systems at higher risk
      • Can also resist other antimicrobial classes
      • In hospitals, isolate and cohort patients with contact precautions

    S. aureus: Pathogenesis (Portal of Entry)

    • Ingestion
    • Penetration
      • A break in the skin
      • Entry through mucous membranes, allowing access to adjoining tissues

    S. aureus: Pathogenesis (Attachment to Cells)

    • Surface proteins
      • Facilitate attachment
      • Capsule
        • Inhibits chemotaxis and phagocytosis
        • Facilitates adherence to implants
    • Fibrin/fibrinogen binding proteins (clumping factor)
      • Attachment to blood clots and traumatized tissue
    • Matrix-binding proteins
      • Promote collagen attachment (causing osteomyelitis or septic arthritis for strains)

    S. aureus: Pathogenesis (Defeating the Immune System)

    • Inhibition of phagocytosis while remaining within phagocytes
    • Production of extracellular substances promoting invasion (Invasins and enzymes)

    S. aureus: Pathogenesis (Damage to Host Cells)

    • Direct damage to peptidoglycan cell walls
    • Enzymes
    • Exotoxins (Superantigens)
      • Toxic shock syndrome toxin (TSST-1)
      • Enterotoxins (A-E, G-I; cause food poisoning)
    • Exfoliative toxins (cause scalded skin syndrome)
    • Other cytotoxins (alpha, beta, leukocidin)

    S. aureus: Pathogenesis (Spread)

    • Person-to-person contact, skin carriage
    • Environment (shedding onto surfaces)

    Classification of Staphylococcal Infections

    • Skin and soft tissue (e.g., boils, carbuncles, furuncles)
    • Systemic/invasive infections (e.g., bloodstream infection [BSI], endocarditis, bone/joint infections, deep abscesses, pneumonia)
    • Toxin-mediated infections (e.g., food poisoning, gastroenteritis, scalded skin syndrome, toxic shock syndrome)

    S. aureus: Systemic Infections

    • Bloodstream infection (BSI)
      • Usually secondary to BSI
      • Covered in more detail in Cardiovascular module
    • Bone/joint infections (e.g., septic arthritis, osteomyelitis)
      • Refer to the lecture
    • Deep abscesses (brain, spine, psoas muscle)
    • Pneumonia
      • Risk factors: viral respiratory infections, cystic fibrosis, ventilation, aspiration
      • Covered in respiratory module

    S. aureus: Toxin-mediated Infection - Scalded Skin Syndrome

    • Spectrum of superficial blistering skin disorders
      • Localized blisters
      • Generalized exfoliation of entire body surface
      • Mucous membranes usually spared
    • Exfoliative toxins spread hematogenously from a localized source
    • Split intracellular bridges in the skin layer (middle layers)
    • Is most common in children under 6, but seen in neonates, immunocompromised adults, and those with renal failure
    • Contagious
    • Mortality: Children <3%, Adults up to 60%

    S. aureus: Toxin-mediated Infection - Toxic Shock Syndrome (TSS)

    • TSS toxin-1 acts as a superantigen
    • Massive cytokine release
    • Historically associated with high-absorbency tampons
    • Rapid, dramatic, and fulminant onset
      • Pyrexia, hypotension, rash (with desquamation)
    • Other organ involvement
      • Renal failure
      • CNS (disorientation without focal neurological signs)
      • Muscular (severe myalgia, increase in CK)

    Laboratory Diagnosis

    • Day 0: Patient specimen (e.g., blood culture)
    • Incubate at 37°C
    • Day 1+: Gram stain (bunches of grapes), lab team review, potentially PCR for confirmation
    • 24 hours later: Read agar culture plates, coagulase test, and phone team/patient review
    • 24 hours later: Alter empiric antibiotic therapy as appropriate, if MRSA, infection control precautions and decolonization

    Management of S. aureus Infection

    • History (especially timing and presentation of symptoms)
    • Clinical examination
      • Focus on a possible source/evidence of spread if systemically unwell
      • Skin (IV sites, indwelling devices, surgical wounds, soft tissue infections or abscesses); remember that scars can be a sign of implanted devices
      • Cardiovascular System (CVS): evidence of known or new/changed murmur
      • Musculoskeletal (new bone or joint pain, reduced range of motion or limp, swelling, loss of function)
    • Investigations (depends on clinical presentation):
    • General blood tests (FBC, U&E, CRP, lactate)
    • Microbiology (specimen depends on infection site)
      • Abscess - pus or tissue biopsy
      • BSI: blood cultures
      • Pneumonia: sputum, bronchoalveolar lavage (BAL)
      • Septic arthritis: joint fluid
      • TSS: next in the slide
      • Food poisoning: food (not stool)
    • Other imaging (e.g., CXR, CT or MRI scans, echocardiogram [ECHO])

    TSS - Investigations & Management

    • Investigations (if febrile or systemically unwell):
      • Blood cultures (rarely positive)
      • Wound swab if skin lesion
      • Other swabs (abscess, cervix/vagina)
    • Management:
      • Quickly recognize and treat for resuscitation and critical care
      • Rapid IV antimicrobials
      • Source control (debriding infected or necrotic wounds, drain abscesses etc.)

    Antibiotic Treatment

    • Choice, route, and duration depend on site and complexity of infection
    • Mild infections (e.g., boil, folliculitis): no treatment
    • Skin/soft tissue infections and respiratory tract infections: 7 days
    • Bloodstream infection: 14 days
    • Complicated infections (e.g., endocarditis, septic arthritis, osteomyelitis): at least four weeks, potentially longer
    • Flucloxacillin if susceptible (MSSA)
    • 1st-generation cephalosporin (e.g., cefazolin) - alternative for options
    • Vancomycin or Teicoplanin (glycopeptides) if MRSA
    • Alternatives: daptomycin, linezolid, tetracyclines
    • If bloodstream infection, consider the source; do ECHO and radiology
    • Repeat blood cultures after commencing antimicrobials
    • Confirm the blood cultures are now sterile

    Epidemiology: S. aureus Bloodstream Infection in Ireland (2018–2022)

    • Chart showing numbers of total and MRSA cases per year. 2022 shows the highest number of total cases.

    Community-Acquired MRSA

    • Skin infections and necrotizing pneumonia
    • Younger patients, healthier patients
    • Less antibiotic resistant, but more virulent
    • Certain strains are common in North America

    Coagulase-negative Staphylococci

    • Natural inhabitants of human skin and mucosa
    • Less virulent than S. aureus; rarely cause infection in healthy individuals
    • S. epidermidis is commonly associated with prosthetic devices (e.g., joint replacements, prosthetic valves, pacemakers)
    • S. saprophyticus causes urinary tract infections
    • Covered again in year 2 REGUB module

    Staphylococcus epidermidis pathogenesis

    • Bacteria adhesion to biomaterial
    • Biofilm formation and tissue cell displacement

    S. epidermidis infections (Devices)

    • Bloodstream infection secondary to IV lines
    • Endocarditis (prosthetic valves)
    • Prosthetic joint infections
    • Continuous ambulatory peritoneal dialysis peritonitis
    • Ventriculitis/shunt-associated meningitis

    Clinical Case 2

    • 65-year-old male with fever and rigors 16 days post-small bowel resection
    • Central venous catheter (CVC) in situ for parenteral nutrition
    • Erythematous skin around CVC insertion site
    • Two sets of blood cultures sent for culture and susceptibility testing

    Diagnosis & Management of CoNS

    • Often patient is not particularly systemically unwell
    • History and examination
    • Blood cultures (at least two sets)
    • Source control (often the prosthesis must come out for effective treatment)
    • Culture prosthetic material
    • Coagulase-negative staphylococci are often antibiotic resistant (including methicillin and flucloxacillin)
    • Vancomycin is the usual empiric treatment
    • Indication and duration of treatment depend on the location of infection and if the prosthetic material can be removed

    Clinical Case 3

    • 72-year-old female with fever and rigors six weeks post-total knee replacement
    • Blood cultures shows:
      • Microscopy: Gram-positive cocci in clusters
      • Catalase: positive
      • Coagulase: negative
    • Most likely causative pathogen is S. epidermidis based on the results - note the lack of coagulase activity

    Understanding Laboratory Results

    • Microscopy: Gram-positive cocci in clusters
    • Catalase: positive
    • Coagulase: positive, indicating S. aureus

    Preventing Staphylococcal Infection

    • Prevent transmission from patient-to-patient
      • Hand hygiene
      • Environmental and equipment hygiene
      • Transmission-based precautions (isolate infected patients, use gloves, aprons/gowns) for MRSA

    Summary: Staphylococci

    • Coagulase +ve (S. aureus)
      • 20-40% of population carries it without infection
      • Common cause of skin and soft-tissue. systemic, and toxin-mediated infections
      • Virulence factors (treatment: flucloxacillin for MSSA, vancomycin for MRSA)
    • Coagulase −ve (S. epidermidis and S. saprophyticus)
      • Often normal flora
      • Rarely pathogenic
      • S. epidermidis: infections are often associated with prosthetic devices, requiring empiric vancomycin treatment
      • S. saprophyticus: causes UTIs

    Virulence Factors of S. aureus

    • Summary of S. aureus virulence factors, with enzyme descriptions, biological roles, and relevant details provided (Table-like format)

    Staphylococcal Biofilm Formation

    • CoNS and MRSA are exceptionally proficient at attaching to surfaces and producing biofilms

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    Related Documents

    RCSI Staphylococci Past Paper PDF

    Description

    Explore the characteristics and classifications of Staphylococci, including coagulase-positive and coagulase-negative types. This quiz also covers essential laboratory tests like the coagulase and catalase tests, which are crucial for differentiating these bacteria. Test your knowledge on these key aspects of microbiology.

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