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Questions and Answers
Which of the following genera are the most important gram-positive cocci?
Which of the following genera are the most important gram-positive cocci?
What is the arrangement of Staphylococcus in a microscope?
What is the arrangement of Staphylococcus in a microscope?
How many species of Staphylococcus are of clinical importance?
How many species of Staphylococcus are of clinical importance?
What is the outcome of Staphylococcus fermenting carbohydrates?
What is the outcome of Staphylococcus fermenting carbohydrates?
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What is the characteristic of Staphylococcus colonies on solid media?
What is the characteristic of Staphylococcus colonies on solid media?
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What is the function of β-lactamase in Staphylococcus?
What is the function of β-lactamase in Staphylococcus?
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What is the characteristic of Staphylococcus in terms of temperature resistance?
What is the characteristic of Staphylococcus in terms of temperature resistance?
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What is the outcome of Staphylococcus producing heat-stable enterotoxins?
What is the outcome of Staphylococcus producing heat-stable enterotoxins?
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What is the characteristic shape of Neisseria species?
What is the characteristic shape of Neisseria species?
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What is the optimal growth condition for Neisseria species?
What is the optimal growth condition for Neisseria species?
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What is the function of the Por protein in Neisseria gonorrhoeae?
What is the function of the Por protein in Neisseria gonorrhoeae?
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What is the primary mechanism of transmission of Neisseria gonorrhoeae?
What is the primary mechanism of transmission of Neisseria gonorrhoeae?
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What is the role of the Opa protein in Neisseria gonorrhoeae?
What is the role of the Opa protein in Neisseria gonorrhoeae?
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What is the effect of Neisseria gonorrhoeae on phagocytes?
What is the effect of Neisseria gonorrhoeae on phagocytes?
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What is a characteristic of Neisseria gonorrhoeae that contributes to its pathogenesis?
What is a characteristic of Neisseria gonorrhoeae that contributes to its pathogenesis?
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Study Notes
The Genus Staphylococcus
- Gram-positive in reaction
- Arranged in grape-like irregular clusters
- Comprises over 30 species, with 3 main species of clinical importance: S. aureus, S. epidermidis, and S. saprophyticus
General Properties
- Grow on many types of media
- Some species are part of the normal human flora (skin and mucous membranes), while others cause infections
- Pathogenic staphylococci can hemolyze blood, coagulate plasma, and produce extracellular enzymes and toxins
Identification
- Can grow on most bacteriological media under aerobic and microaerophilic conditions
- Grow rapidly at 35-37°C
- Colonies on solid media are round, smooth, and raised
- S. aureus forms gray to deep golden yellow colonies, while S. epidermidis produces gray to white colonies
Growth Characteristics
- Produce catalase, which converts H2O2 into H2O and O2
- Ferment carbohydrates, releasing lactic acid but not gas
- Produce many extracellular substances
- Resistant to drying, heat (50°C for 30 minutes), and 9% NaCl
- Variable sensitivity to many antibiotics (ABCs)
- Some species produce β-lactamase due to plasmid genes, making them resistant to ampicillin, tetracycline, and aminoglycosides
Antigenic Structure
- Contain antigenic polysaccharides, peptidoglycan, teichoic acids, proteins, and other substances like capsules and coagulase (in S. aureus)
Toxins and Enzymes
- Enzymes:
- Catalase, which converts H2O2 into H2O and O2, differentiating staphylococci from streptococci
- Coagulase, produced by S. aureus, which clots plasma, deposits fibrin on the surface of staphylococci, inhibits phagocytosis, and is associated with pathogenicity
General Characteristics of Neisseria
- Non-motile, gram-negative, intracellular diplococci that ferment carbohydrates, producing acid but not gas
- Kidney-shaped with adjacent concave sides
Optimal Growth Conditions
- Grow best on complex media under aerobic conditions containing 5% CO2
- Require heated blood, hemin, animal protein, and other supplements for growth
Medical Importance
- Two main species of medical importance: N. meningitidis and N. gonorrhoeae
- Neisseria species are sensitive to drying, sunlight, moist heat, and disinfectants
Neisseria gonorrhoeae
General Characteristics
- Obligate parasite of the human urogenital tract
- Has no polysaccharide capsule but has multiple serotypes based on pilus protein antigenicity
- More than 100 serotypes are known due to antigenic variation in gonococcal pili
Virulence Factors
- Pili: mediate initial attachment to non-ciliated human cells, resist phagocytosis
- Por protein (Protein I): forms pores on the surface of bacteria, promotes intracellular survival by preventing phagolysosome fusion in neutrophils
- Opa (Protein II): important for firm attachment and invasion of host cells
- Lipooligosaccharide (LOS): responsible for symptoms/toxicity of gonorrhea, triggers intense inflammatory response, and activates complement
Pathogenesis and Clinical Manifestations
- Transmitted by sexual contact
- Gonococci attack mucous membranes of the GUT, eye, rectum, and throat
- In males, causes urethritis with yellow, creamy pus and painful urination
- In females, primary infection is in the endo-cervix, extending to the cervix and vagina, causing mucopurulent discharge
- Can cause gonococcal ophthalmia neonatorum in newborns
Laboratory Diagnosis
- Specimen: Urethral swab
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Description
This quiz covers the two main genera of gram positive cocci, including Staphylococcus and Streptococcus, and their characteristics. Learn about the general properties and clinically important species of Staphylococcus.
