Questions and Answers
What are the general characteristics of Staphylococcus species?
Which of the following species is known for causing Toxic Shock Syndrome?
Which virulence factor produced by Staphylococcus aureus is known to cause Scalded Skin Syndrome?
What is a notable biochemical characteristic of Staphylococcus species?
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Which environment can support the growth of Staphylococcus species?
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Which specific enzyme is a virulence factor of Staphylococcus aureus and is involved in clot formation?
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Where is the primary reservoir for staphylococci located in humans?
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Which of the following is NOT a characteristic of Staphylococcus aureus?
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Which condition is characterized by the formation of pus-filled boils?
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Which Staphylococcus species is known for causing urinary tract infections in sexually active young females?
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What type of infections can Staphylococcus lugdunensis most commonly mimic?
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Which of the following best describes the cultural characteristics of Staphylococcus aureus on blood agar after 18-24 hours?
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What is a notable characteristic of Staphylococcus epidermidis?
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Which enterotoxin type is NOT associated with food poisoning caused by Staphylococcus aureus?
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Which of the following is a common laboratory method for isolating Staphylococcus aureus?
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Which Staphylococcus species is commonly isolated but may have vancomycin resistance?
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What indicates a positive catalase test result?
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Which test detects the ability of bacteria to convert fibrinogen to fibrin?
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What is the significance of observing a zone diameter greater than 10mm in the bacitracin susceptibility test?
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In the microdase test, what result indicates a positive test?
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What does a clear zone surrounding growth in the Dnase test signify?
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What is required for a valid result in the tube coagulase test after initial incubation?
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What does growth with fermentation result in on mannitol salt agar?
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In the novobiocin susceptibility test, what does a zone diameter less than 16mm indicate?
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Study Notes
General Characteristics of Staphylococci
- Gram-positive cocci, appearing in pairs, tetrads, or clusters.
- Non-motile and non-spore forming; facultative anaerobes.
- Catalase-positive and oxidase-negative; can grow in environments with 7.5-10% NaCl.
- Colonies are medium-sized (4-8 mm), cream, white, or light gold, with a buttery appearance.
- Some species exhibit β-hemolytic activity.
Clinically Significant Staphylococci Species
- Staphylococcus aureus
- Staphylococcus epidermidis
- Staphylococcus saprophyticus
- Staphylococcus lugdunensis
- Staphylococcus haemolyticus
Staphylococcus aureus
Virulence Factors
- Enterotoxins: Heat-stable toxins (A-E, G-J), associated with food poisoning.
- Toxic Shock Syndrome Toxin-1: A superantigen, linked to menstruation-associated TSS.
- Exfoliative Toxin: Causes Staphylococcal Scalded Skin Syndrome and Bullous Impetigo.
- Cytolytic Toxins: Hemolysins including α, β, δ, and γ types.
- Enzymatic Factors: Coagulase, fibrinolysin, protease, hyaluronidase, lipase, and beta-lactamase (penicillinase).
- Protein A: Binds to the Fc portion of IgG, impeding opsonization.
Epidemiology
- Human colonization primarily occurs in the nasal passages, axillae, vagina, and skin.
- Transmission occurs via direct contact with unwashed hands or contaminated surfaces.
Infections and Associated Diseases
- Common infections include:
- Skin and wound infections (folliculitis, furuncles, carbuncles).
- Staphylococcal Scalded Skin Syndrome (SSS).
- Toxic Shock Syndrome (TSS).
- Tenosynovitis (TEN).
- Food poisoning due to enterotoxins.
Staphylococcus epidermidis
- Produces exopolysaccharide slime, enhancing adhesion to medical devices and resisting host defenses.
- Associated diseases include healthcare-acquired UTIs and prosthetic valve endocarditis.
Staphylococcus saprophyticus
- Strong adherence to epithelial cells of the urogenital tract.
- Primarily causes UTIs in sexually active young females.
Staphylococcus lugdunensis
- Exhibits higher virulence, mimicking S. aureus infections.
- Carries the mecA gene for oxacillin resistance.
- Associated infections include infective endocarditis, septicemia, and urinary tract infections.
Staphylococcus haemolyticus
- Common coagulase-negative staphylococci (CoNS), with some isolates showing vancomycin resistance.
- Associated diseases include skin infections, bacteremia, endocarditis, and UTIs.
Laboratory Diagnosis
Isolation and Identification
- Specimens collected: aspirates or swabs.
- Culture media options include blood agar, colistin-nalidixic acid, phenylethyl alcohol, and mannitol salt agar.
Cultural Characteristics
- Staphylococci form round, smooth, white to creamy colonies on SBA after 18-24 hours.
Key Diagnostic Tests
- Catalase Test: Positive results show bubble formation.
- Coagulase Test: Differentiates S. aureus (positive) from other staphylococci (negative).
- Microdase Test: Detects oxidase enzyme presence.
- Bacitracin and Novobiocin Susceptibility Tests: Determines susceptibility or resistance to bacitracin and novobiocin.
- DNase Test: Checks for DNA hydrolysis capability, indicated by a clear zone.
- Mannitol Salt Agar: Evaluates mannitol fermentation; growth with fermentation shows yellow halos, no fermentation remains pink/red.
Antimicrobial Susceptibility
- Testing is based on the source of the isolate and whether it is a contaminant or active pathogen.
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Description
This quiz covers the general characteristics and clinically significant species of Staphylococcus. You'll explore their morphology, virulence factors, and pathogenic mechanisms, particularly focusing on Staphylococcus aureus. Ideal for students studying microbiology or infectious diseases.
