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Questions and Answers
What color do the endopigments produced by S.aureus appear?
Which of the following statements is true about S.aureus?
What type of bacteria are all staphylococci classified as based on their catalase activity?
Which drug class is effective against S.aureus due to its penicillinase production?
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In an immunocompromised individual, what is a common infection associated with S.aureus?
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Which of the following characteristics are true about S.aureus?
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What is a common manifestation of Staphylococcal infections in neonates?
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Which toxin produced by S.aureus contributes to food poisoning?
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What is the main function of the cell wall associated proteins in S.aureus?
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What typical laboratory diagnosis method is used for S.aureus infections?
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S.aureus is a major pathogen for humans and is commonly found as flora in which regions?
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What is a significant complication of Toxic Shock Syndrome (TSS) caused by S.aureus?
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What is the optimum growth temperature for S.aureus?
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What is the most likely diagnosis for the infant presenting with extensive blisters and skin exfoliation following maternal staphylococcal mastitis?
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How does S.aureus typically appear when observed under a Gram stain?
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Which of the following toxins is responsible for the disease process in Staphylococcal Scalded Skin Syndrome?
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What biochemical property distinguishes S.aureus from other staphylococci?
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Which type of infections is S.aureus commonly associated with in young females?
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Which enzyme produced by S.aureus is responsible for converting prothrombin to thrombin?
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What is the primary mechanism through which S.aureus enhances its survival within phagocytes?
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Which of the following diseases is not typically associated with S.aureus infections?
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The toxin responsible for scalded skin syndrome in neonates produced by S.aureus is known as what?
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Which option accurately describes the characteristics of S.epidermidis compared to S.aureus?
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What is a key feature of food poisoning caused by S.aureus?
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In the context of S.aureus infections, which sample type is least likely to be used for laboratory diagnosis?
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Which factor contributes to the ability of S.aureus to inhibit opsonization?
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Study Notes
Staphylococcal Infections
- Gram-positive cocci that appear in clusters
- Non-motile and non-spore forming
- S. aureus forms a microcapsule, while other species may produce a slime layer
Key Species
-
S. aureus is a major pathogen found in humans
- Commonly found on skin and in the upper respiratory tract (10-40% of individuals carry S. aureus in their anterior nares)
- S. epidermidis is normal flora
- S. saprophyticus can cause UTIs in young females
Virulence Factors
- Cell wall associated proteins and polymers
- Inhibit phagocytosis and chemotaxis
- Protein A binds to the Fc portion of IgG, inhibiting opsonization
- Enzymes and toxins produced by S. aureus:
- Coagulase: converts prothrombin to thrombin, which converts fibrinogen to fibrin, coating the bacterial cell and interfering with opsonization and phagocytosis
- Catalase: inactivates toxic H2O2 inside phagocytes, enhancing survival of S. aureus within phagocytes
- Proteases, lipase and DNase
Toxins
- Haemolysin: destroys red blood cells
- Leucocidin: destroys white blood cells
- Enterotoxins: Cause food poisoning when ingested
- Heat and acid stable
- 5 types (A, B, C, D, E)
- Toxic Shock Syndrome Toxin (TSST): Causes toxic shock syndrome
- Epidermolytic (exfoliative) toxin: Causes scalded skin syndrome in neonates
Clinical Manifestations
- Skin infections: Boils, stye, furunculosis, abscesses, acute endocarditis
- Pneumonia and Bacteremia
- Hospital acquired (nosocomial) infections: UTI, phlebitis
Scalded Skin Syndrome
- Widespread blistering
- Loss of the epidermis in neonates
- Caused by the production of epidermolytic (exfoliative) toxins
Food Poisoning
- Occurs from improperly cooked food, such as milk
- Five enterotoxins are involved
- Symptoms develop within 1-6 hours
- Includes vomiting and diarrhea
- Fluid therapy may be necessary; often self-limited
Toxic Shock Syndrome (TSS)
- Characterized by skin desquamation and shock (hypotension)
- Often occurs in young females during menstruation due to the presence of TSST in tampons
Diagnosis
- Swabs, pus, sputum, CSF, and blood samples based on the site of infection
- Gram stain for characteristic morphology
- Facultative anaerobes, optimum temperature of 37°C, normal atmospheric CO2
- Can grow on ordinary media
- S. aureus produces golden yellow endopigments
- S. aureus causes α-hemolysis on blood agar
- Selective media: mannitol salt agar, where S. aureus ferments mannitol, and salt inhibits other normal flora
Laboratory Identification
- Film stained by Gram for characteristic morphology
- Biochemical reactions:
- All staphylococci are catalase positive
- S. aureus is coagulase and DNAase positive and ferments mannitol
Treatment
- Penicillinase-resistant β-lactams are used to select an effective drug
S. epidermidis
- Normal flora of the skin, non-pathogenic
- Can cause infections in immunocompromised individuals
S. saprophyticus
- Commonly causes UTIs in young females
- Can cause infections on prosthetic implants such as heart valves and hip joints
Case Study
- A 2-month-old female infant presents with extensive blisters
- Mother had suffered from staphylococcal mastitis one week prior
- On examination:
- Blisters are fluid-filled, have thin walls, rupture easily
- Skin redness (erythema) covers most of the body
- Large areas of the skin are exfoliated and painful
Case Diagnosis
- Likely diagnosis: Scalded skin syndrome
Causative Organism
- Most likely causative organism: S. aureus
Toxin Responsible
- Toxin responsible for the disease: Epidermolytic (exfoliative) toxin
Appearance in Direct Smear
- S. aureus appears in clusters in a direct smear
Other Toxigenic Diseases
- Two other toxigenic diseases caused by S. aureus:
- Food poisoning
- Toxic shock syndrome
Staphylococcal Infections
- Gram-positive cocci that appear in clusters
- Non-motile and non-spore forming
- S. aureus forms a microcapsule
- Other species may produce slime layers
- Major human pathogen, found as normal flora on the skin and upper respiratory tract
-
S. aureus can produce several virulence factors which contribute to infection
-
Cell wall associated proteins and polymers
- Inhibit phagocytosis and chemotaxis
- Major protein in the cell wall
- Binds to the Fc portion of IgG
- Inhibits opsonization
-
Enzymes and toxins
- Coagulase converts prothrombin to thrombin, which converts fibrinogen to fibrin
- Catalase inactivates toxic H2O2 inside phagocytes to enhance survival of S. aureus
- Proteases, lipase, and DNase
- Haemolysin
- Leucocidin
-
Enterotoxins cause food poisoning
- Heat and acid-stable
- 5 types (A, B, C, D, E)
- Cause vomiting and diarrhea
- Toxic shock syndrome toxin (TSST) causes toxic shock syndrome
- Epidermolytic (exfoliative) toxin causes scalded skin syndrome
-
Cell wall associated proteins and polymers
Diseases Caused by S. aureus
- Skin infections: boils, styes, and furunculosis
- Abscesses and acute endocarditis
- Pneumonia and bacteremia
- Hospital-acquired (nosocomial) infections: urinary tract infections and phlebitis
-
Scalded skin syndrome:
- Widespread blistering
- Loss of the epidermis in neonates
- Caused by the epidermolytic (exfoliative) toxin
-
Food poisoning:
- Caused by contaminated food, such as improperly cooked milk
- Five different enterotoxins
- Onset occurs within 1-6 hours
- Symptoms include vomiting and diarrhea
- Usually self-limiting, treatment involved fluid therapy
-
Toxic shock syndrome (TSS):
- Characterized by skin desquamation and shock (hypotension)
- Often caused by TSST in young females during menstruation, associated with tampon use
Diagnosis of S. aureus Infections
- Specimen types: swabs, pus, sputum, CSF, blood
- Gram stain: reveals characteristic morphology of cocci in clusters
- Culture: facultative anaerobes, optimum temperature of 37 degrees Celsius
- Growth on ordinary media: S. aureus produces a golden yellow endopigment
- Blood agar: S. aureus exhibits α-hemolysis
- Selective Media: Mannitol salt agar, S. aureus ferments mannitol, salt inhibits other normal flora
-
Biochemical reactions:
- Catalase positive: distinguishes staphylococci from streptococci
- Coagulase positive: differentiates S. aureus from other staphylococci
- DNAase positive: differentiates S. aureus from other staphylococci
- Mannitol fermentation: positive for S. aureus
Treatment of S. aureus Infections
- Antibiotic susceptibility testing is essential to identify the appropriate treatment
- Penicillinase-resistant β-lactams often used, as S. aureus can produce penicillinase
Other Staphylococcal Species
- S. epidermidis: normal flora of the skin, usually nonpathogenic
- S. saprophyticus: can cause infections in immunocompromised individuals and UTIs in young females
Case Study
- Diagnosis: Scalded skin syndrome (SSSS)
- Causative organism: Staphylococcus aureus
- Toxin responsible: Epidermolytic toxin (Exfoliatin)
- Appearance in direct smear: Gram-positive cocci in clusters
-
Other toxigenic diseases caused by S. aureus:
- Toxic shock syndrome (TSS)
- Food poisoning
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Description
This quiz covers the essential aspects of Staphylococcal infections, focusing on key species such as S. aureus, S. epidermidis, and S. saprophyticus. Explore the virulence factors, transmission methods, and clinical significance of these Gram-positive cocci. Test your understanding of their pathogenicity and role in human health.
