Podcast
Questions and Answers
Which characteristic is true about Staphylococcus aureus?
Which characteristic is true about Staphylococcus aureus?
- It forms spores.
- It grows in the presence of 5% NaCl.
- It is catalase negative.
- It can reduce nitrates to nitrites. (correct)
What distinguishes Stomatococcus mucilaginosus from other cocci?
What distinguishes Stomatococcus mucilaginosus from other cocci?
- It is a common pathogen in healthy individuals.
- It is catalase positive.
- It can grow in 5% NaCl.
- It has been reclassified under the genus Rothia. (correct)
Which diseases are commonly caused by Staphylococcus aureus?
Which diseases are commonly caused by Staphylococcus aureus?
- Urinary tract infections and meningitis.
- Enteritis and gastroenteritis.
- Tuberculosis and pneumonia.
- Folliculitis and impetigo. (correct)
What is a notable virulence factor of Staphylococcus epidermidis?
What is a notable virulence factor of Staphylococcus epidermidis?
How does Staphylococcus saprophyticus differ from other coagulase negative staphylococci?
How does Staphylococcus saprophyticus differ from other coagulase negative staphylococci?
Which of the following toxins is associated with Staphylococcus aureus?
Which of the following toxins is associated with Staphylococcus aureus?
What laboratory culture condition helps to identify Staphylococcus species?
What laboratory culture condition helps to identify Staphylococcus species?
What is the drug of choice for treating MRSA infections?
What is the drug of choice for treating MRSA infections?
Flashcards
Gram-Positive Cocci
Gram-Positive Cocci
A group of bacteria that are gram-positive, cocci-shaped, and commonly found on the skin and mucous membranes. They are known for their ability to cause infections, particularly pyogenic infections (pus-forming).
Staphylococcus
Staphylococcus
A genus of gram-positive cocci that are catalase-positive. They are known for their ability to cause a variety of infections, including skin infections, food poisoning, and toxic shock syndrome.
Staphylococcus aureus (S. aureus)
Staphylococcus aureus (S. aureus)
A species of Staphylococcus that is known for being a major human pathogen. It is often associated with skin infections, but can also cause serious infections like pneumonia and endocarditis.
Coagulase
Coagulase
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Scalded Skin Syndrome
Scalded Skin Syndrome
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Toxic Shock Syndrome (TSS)
Toxic Shock Syndrome (TSS)
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Staphylococcus epidermidis (S. epidermidis)
Staphylococcus epidermidis (S. epidermidis)
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Staphylococcus saprophyticus (S. saprophyticus)
Staphylococcus saprophyticus (S. saprophyticus)
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Study Notes
Gram-Positive Cocci
- Gram-positive cocci have a high peptidoglycan content and low lipid in their cell walls.
- They are common inhabitants of skin and mucous membranes.
- Infections often result from direct contact.
- Pyogenic infections (pus formation) can be caused by staphylococcal infections.
- Clinically significant genera include Staphylococcus (catalase-positive) and Streptococcus (catalase-negative).
Stomatococcus mucilaginosus
- The only member of the genus Stomatococcus.
- Recently reclassified as Rothia mucilaginosus.
- Normal flora of the respiratory tract.
- Cannot grow in the presence of 5% NaCl.
- Weakly catalase-positive, coagulase-negative, and has a capsule.
- Can be an emerging pathogen in immunocompromised individuals.
Staphylococcus
- Common isolates include S. aureus, S. epidermidis, and S. saprophyticus.
- Gram-positive cocci, catalase-positive.
- Nonmotile and non-spore-forming bacteria.
- Facultative anaerobes.
- Modified oxidase-negative.
- Reduce nitrates to nitrites.
- Grow in 7.5% to 10% NaCl (mannitol salt agar).
- Susceptible to lysostaphin, resistant to bacitracin.
Staphylococcus aureus (SAU)
- Virulence factors:
- Surface structures: Protein A, capsular polysaccharide, peptidoglycan, teichoic acid
- Enzymes: Catalase, bound coagulase (clotting factor), free coagulase (tube coagulase), staphylokinase, lipase, hyaluronidase, DNase, β-lactamase
- Toxins: Exfoliatin, leukocidin, hemolysins, enterotoxins, superantigens (TSST-1).
- Diseases:
- Local abscesses (folliculitis, furuncles, carbuncles, sty)
- Focal suppuration (osteomyelitis, pneumonia, meningitis, empyema, endocarditis, sepsis, impetigo)
- Exotoxin elaboration (food poisoning, scalded skin syndrome, toxic shock syndrome)
Staphylococcus epidermidis
- Virulence factor: Biofilm production, adherence to surfaces of prosthetic devices.
- Gram-positive cocci, catalase-positive, coagulase-negative, and DNAse-negative.
- White and creamy, nonhemolytic growth on blood agar plates (BAP).
- Grows on Columbia Nalidixic Agar (CNA).
- Does not ferment mannitol on mannitol salt agar.
- Susceptible to novobiocin.
- Commonly associated with hospital-acquired infections (nosocomial).
Staphylococcus saprophyticus
- Primarily causes urinary tract infections (UTIs) in sexually active women.
- Associated with catheter-associated UTIs.
- Gram-positive cocci, catalase-positive, coagulase-negative, and DNAse-negative.
- Nonhemolytic growth on blood agar plates (BAP).
- Mannitol salt agar fermentation varies.
- Resistant to novobiocin (zone of inhibition ≥16mm is considered susceptible).
Methicillin-Resistant Staphylococcus aureus (MRSA)
- Methicillin-resistant S. aureus (MRSA) strains are resistant to beta-lactam antibiotics.
- Oxacillin, cloxacillin, and methicillin are common drugs used to treat MRSA infections.
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Description
This quiz explores the characteristics and clinical significance of gram-positive cocci, including the genera Staphylococcus and Streptococcus. It covers their role in infections, normal flora, and the specific features of Stomatococcus mucilaginosus. Test your knowledge on these important pathogens!
