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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?
What is the primary mechanism by which aureus causes diseases such as toxic shock syndrome and staphylococcal food poisoning?
Which disease results from the activity of exfoliative toxins produced by aureus?
Which disease results from the activity of exfoliative toxins produced by aureus?
What is a key characteristic that differentiates bullous impetigo from Staphylococcal Scalded Skin Syndrome (SSSS)?
What is a key characteristic that differentiates bullous impetigo from Staphylococcal Scalded Skin Syndrome (SSSS)?
What defines the stability of staphylococcal enterotoxins in terms of temperature and digestive enzymes?
What defines the stability of staphylococcal enterotoxins in terms of temperature and digestive enzymes?
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What is a common outcome associated with diseases caused by the proliferation of aureus bacteria?
What is a common outcome associated with diseases caused by the proliferation of aureus bacteria?
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Which statement accurately describes the characteristics of Staphylococcus species?
Which statement accurately describes the characteristics of Staphylococcus species?
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What feature distinguishes Staphylococcus aureus from other staphylococcal species?
What feature distinguishes Staphylococcus aureus from other staphylococcal species?
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How does Staphylococcus aureus primarily resist phagocytosis?
How does Staphylococcus aureus primarily resist phagocytosis?
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What is the primary reservoir for Staphylococcus aureus in the human population?
What is the primary reservoir for Staphylococcus aureus in the human population?
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What is the primary cause of death in patients with Toxic Shock Syndrome (TSS)?
What is the primary cause of death in patients with Toxic Shock Syndrome (TSS)?
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Which of the following statements about the growth conditions of Staphylococcus aureus is true?
Which of the following statements about the growth conditions of Staphylococcus aureus is true?
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What is the primary role of Protein A in Staphylococcus aureus?
What is the primary role of Protein A in Staphylococcus aureus?
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Which method is considered the gold standard for the laboratory diagnosis of Staphylococcus aureus?
Which method is considered the gold standard for the laboratory diagnosis of Staphylococcus aureus?
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What characteristic of S.aureus allows it to be selectively isolated on mannitol-salt agar?
What characteristic of S.aureus allows it to be selectively isolated on mannitol-salt agar?
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What feature of Staphylococcus aureus colonies can be visually identified as a distinguishing characteristic?
What feature of Staphylococcus aureus colonies can be visually identified as a distinguishing characteristic?
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Which condition is primarily associated with the presence of Large skin lesions and peeling?
Which condition is primarily associated with the presence of Large skin lesions and peeling?
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What is the primary function of MSCRAMM proteins in Staphylococcus aureus?
What is the primary function of MSCRAMM proteins in Staphylococcus aureus?
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What is a typical symptom of septic arthritis?
What is a typical symptom of septic arthritis?
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Which test is specifically used for biochemical identification of S.aureus?
Which test is specifically used for biochemical identification of S.aureus?
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What combination of antibiotics is commonly used for empirical treatment of serious pneumococcal infections?
What combination of antibiotics is commonly used for empirical treatment of serious pneumococcal infections?
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Which of the following conditions is associated with the destruction of bones?
Which of the following conditions is associated with the destruction of bones?
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What is a characteristic of MRSA strains?
What is a characteristic of MRSA strains?
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Which of the following is a recommended vaccine for infants younger than 2 years?
Which of the following is a recommended vaccine for infants younger than 2 years?
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What is the primary reason enterococci are considered nosocomial pathogens?
What is the primary reason enterococci are considered nosocomial pathogens?
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What characteristic can be observed in Bile Esculin agar when enterococci are present?
What characteristic can be observed in Bile Esculin agar when enterococci are present?
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Which of the following antibiotics is known to have a resistance issue with Streptococcus pneumoniae?
Which of the following antibiotics is known to have a resistance issue with Streptococcus pneumoniae?
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What characterizes early-onset disease caused by Streptococcus agalactiae?
What characterizes early-onset disease caused by Streptococcus agalactiae?
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At what gestational weeks should pregnant women be screened for Streptococcus agalactiae?
At what gestational weeks should pregnant women be screened for Streptococcus agalactiae?
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What is the major protective antigen of Streptococcus pneumoniae?
What is the major protective antigen of Streptococcus pneumoniae?
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Which of the following infections can be caused by Streptococcus pneumoniae?
Which of the following infections can be caused by Streptococcus pneumoniae?
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What indicates the autolysis process of Streptococcus pneumoniae colonies on agar?
What indicates the autolysis process of Streptococcus pneumoniae colonies on agar?
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Which of the following describes the Gram-staining characteristics of Streptococcus pneumoniae?
Which of the following describes the Gram-staining characteristics of Streptococcus pneumoniae?
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What complications may arise in adult patients infected with Streptococcus agalactiae?
What complications may arise in adult patients infected with Streptococcus agalactiae?
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Which of the following statements is true regarding the teichoic acids in Streptococcus pneumoniae?
Which of the following statements is true regarding the teichoic acids in Streptococcus pneumoniae?
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What is the primary purpose of IgA-protease in the context of colonization by S.pneumoniae?
What is the primary purpose of IgA-protease in the context of colonization by S.pneumoniae?
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Which of the following correctly describes the method of transmission of S.pneumoniae?
Which of the following correctly describes the method of transmission of S.pneumoniae?
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What is a distinguishing feature of pneumococcal pneumonia onset?
What is a distinguishing feature of pneumococcal pneumonia onset?
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In which bodily fluid would you expect to find pneumococcal antigens during disease detection?
In which bodily fluid would you expect to find pneumococcal antigens during disease detection?
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Which type of sample is most commonly used for culture to detect S.pneumoniae?
Which type of sample is most commonly used for culture to detect S.pneumoniae?
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What is the significance of pneumolysin in S.pneumoniae infection?
What is the significance of pneumolysin in S.pneumoniae infection?
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What percentage of patients surviving pneumococcal meningitis may experience neurological sequelae?
What percentage of patients surviving pneumococcal meningitis may experience neurological sequelae?
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What laboratory test can directly identify S.pneumoniae from cerebrospinal fluid?
What laboratory test can directly identify S.pneumoniae from cerebrospinal fluid?
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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.
