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Questions and Answers
What type of hemolysis is exhibited by Streptococcus pneumoniae?
What type of hemolysis is exhibited by Streptococcus pneumoniae?
Which of the following diseases is caused by Streptococcus pyogenes?
Which of the following diseases is caused by Streptococcus pyogenes?
What is the primary virulence factor responsible for adherence to host cells in Streptococcus pyogenes?
What is the primary virulence factor responsible for adherence to host cells in Streptococcus pyogenes?
Which of the following is a characteristic of viridans streptococci?
Which of the following is a characteristic of viridans streptococci?
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What type of organism is Streptococcus agalactiae primarily known to cause infections in?
What type of organism is Streptococcus agalactiae primarily known to cause infections in?
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What culture conditions are optimal for Neisseria species?
What culture conditions are optimal for Neisseria species?
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Which of the following is NOT a disease caused by Streptococcus pyogenes?
Which of the following is NOT a disease caused by Streptococcus pyogenes?
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What is the mode of transmission for Neisseria gonorrhoeae?
What is the mode of transmission for Neisseria gonorrhoeae?
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Which type of hemolytic streptococci is responsible for complete hemolysis?
Which type of hemolytic streptococci is responsible for complete hemolysis?
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Which organism is known to cause infective endocarditis?
Which organism is known to cause infective endocarditis?
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What is the primary characteristic of coagulase-positive Staphylococci?
What is the primary characteristic of coagulase-positive Staphylococci?
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Which of the following is a virulence factor of Staphylococcus aureus?
Which of the following is a virulence factor of Staphylococcus aureus?
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What type of infections is primarily associated with Staphylococcus aureus?
What type of infections is primarily associated with Staphylococcus aureus?
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Streptococci can be differentiated based on what criterion?
Streptococci can be differentiated based on what criterion?
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What is a characteristic of Staphylococcus epidermidis?
What is a characteristic of Staphylococcus epidermidis?
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What type of bacteria are Staphylococci classified as?
What type of bacteria are Staphylococci classified as?
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Which toxin is responsible for scalded skin syndrome caused by Staphylococcus aureus?
Which toxin is responsible for scalded skin syndrome caused by Staphylococcus aureus?
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Which of the following statements about Staphylococci is true?
Which of the following statements about Staphylococci is true?
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Which Streptococcus species is known for forming chains and is associated with pyogenic infections?
Which Streptococcus species is known for forming chains and is associated with pyogenic infections?
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Which disease is NOT caused by Staphylococcus aureus?
Which disease is NOT caused by Staphylococcus aureus?
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Study Notes
Lecture 6: Medical Bacteriology (I) - Cocci Bacteria
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Types of Bacteria:
- Pathogenic: Cause disease in humans
- Commensal: (Normal flora/human microbiome): Normally inhabit the human body
Gram-Positive Cocci (Staphylococci)
- Morphology: Gram-positive cocci arranged in grape-like clusters
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Culture & Biochemical Characteristics:
- Facultative anaerobes
- Grow at 37°C
- Grow on nutrient agar and blood agar
- All Staphylococci are catalase-positive
Classification of Staphylococci
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Coagulase-positive:
- Staphylococcus aureus (Most pathogenic)
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Coagulase-negative:
- Staphylococcus epidermidis (Normal skin flora)
- Staphylococcus saprophyticus
Virulence Factors of Staphylococcus aureus
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Toxins:
- Epidermolytic (exfoliative) toxin
- Enterotoxin
- Toxic shock syndrome toxin
- Hemolysin
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Enzymes:
- Coagulase
- Staphylokinase
- Catalase
- Proteases, Lipase, DNase
Diseases Caused by Staphylococcus aureus
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Suppurative (pyogenic):
- Skin infections: Boils, Folliculitis, Impetigo
- Bacteremia
- Endocarditis, Osteomyelitis, Pneumonia, Urinary tract infections
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Toxigenic Diseases:
- Scalded skin syndrome
- Food poisoning
- Toxic Shock Syndrome
2- Streptococci
- Morphology: Gram-positive cocci arranged in pairs (e.g., S. pneumoniae) or in chains (e.g., S. pyogenes)
- Some strains are capsulated
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Culture & Biochemical Characteristics:
- Facultative anaerobes
- Grow at 37°C
- Catalase-negative.
- Grow on blood agar
Classification of Streptococci (hemolytic activity)
- Alpha-hemolytic: (partial hemolysis) - S. pneumoniae, S. viridans
- Beta-hemolytic: (complete hemolysis) - Group A Streptococci (S.Pyogenes), Group B Streptococci (S. agalactiae)
- Gamma-hemolytic: (no hemolysis) - Enterococcus faecalis
Virulence Factors of Streptococcus pyogenes
- M protein: Adherence to cells; resistance to phagocytosis
- Enzymes: Streptokinase, Streptodornase, Hyaluronidase, Streptolysins (S & O)
- Exotoxins: Erythrogenic toxin
Diseases Caused by Streptococcus pyogenes
- Suppurative infections: Pharyngitis, Tonsillitis, Sinusitis, Otitis media, Impetigo, Cellulitis, Bacteremia, Puerperal sepsis, Endocarditis, Osteomyelitis
- Toxigenic diseases: Scarlet fever, Streptococcal toxic shock-like syndrome, (due to erythrogenic toxin)
- Post-streptococcal sequelae: Acute rheumatic fever, Acute glomerulonephritis
Other Streptococci and Bacteria
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Streptococcus agalactiae: (normal flora of the vagina); Neonatal meningitis, Neonatal pneumonia
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Viridans Streptococci: (normal flora of the mouth); Dental caries, Infective endocarditis
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S. pneumoniae: Pneumonia, Meningitis
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Enterococcus faecalis: Normal flora in GIT → Urinary tract infection (UTI)
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Gram-negative cocci (Neisseria species):
- Morphology: Gram-negative cocci arranged in pairs (diplococci)
- Culture conditions: Facultative anaerobes, grow at 37°C, Capnophilic (need 5-10% CO2), grow best on chocolate agar and Thayer-Martin agar (selective media)
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Important species of Neisseria:
- Neisseria meningitidis: Mode of transmission - inhalation of infected droplets; Diseases: Meningitis
- Neisseria gonorrhoeae: Mode of transmission - sexually transmitted disease; Diseases: Gonorrheal urethritis or cervicitis, Ophthalmia neonatorum
Case Study
- Case: 1-year-old with fever and generalized convulsion, mild throat inflammation, neck rigidity, clear lungs, Gram-negative diplococci in CSF
- Most likely Causative Pathogen: Neisseria meningitidis
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