15 Questions
Staphylococcus aureus is the least important human pathogen among the Staphylococci family.
False
The genus Staphylococcus is derived from the Greek words 'Staphyle' meaning berry and 'Kokkos' meaning bunch of grapes.
False
Staphylococci are anaerobic bacteria.
False
The optimal temperature for Staphylococci growth is 25°C.
False
Staphylococci colonies on Blood agar are surrounded by a clear zone of alpha-hemolysis.
False
On MacConkey agar, Staphylococci colonies are larger than those on Nutrient agar.
False
Staphylococcus aureus ferments lactose but not mannitol.
False
Mannitol salt agar is a useful selective medium for recovering Staphylococcus epidermidis from faecal specimens.
False
Staphylococcus aureus produces gas during the fermentation of glucose.
False
What is the characteristic of Neisseria morphology?
They are kidney bean shaped and occur in pairs.
What is the primary function of vancomycin in selective media for Neisseria growth?
To suppress the growth of Gram-positive bacteria.
Which of the following Neisseria species can grow under anaerobic conditions?
N. gonorrhoeae
What is the purpose of colistin in selective media for Neisseria growth?
To suppress the growth of Gram-negative bacteria.
What is the optimal condition for Neisseria growth?
Aerobic conditions
Which of the following media is not suitable for N. meningitidis growth?
Nutrient agar
Study Notes
Neisseria
- Gram-negative cocci, occurring in pairs (diplococci)
- Exclusively pathogenic for humans, typically found associated with or inside polymorphonuclear cells (PMNs)
- Two main species: Neisseria gonorrhoeae (gonococci) and Neisseria meningitidis (meningococci)
- Morphology: approximately 0.8 µm in diameter, kidney bean-shaped, flat or concave sides adjacent when in pairs
- Culture: grows on sheep blood agar, chocolate agar, and selective agar media
- Selective media contain vancomycin, colistin, and other inhibitory substances to suppress growth of commensal microorganisms
- N. gonorrhoeae requires enriched chocolate agar and/or selective media for optimal growth
- N. meningitidis grows on sheep blood agar as well as selective media
Growth Characteristics
- Neisseriae grow best under aerobic conditions
- Some Neisseria species (e.g., N. gonorrhoeae) can grow under anaerobic conditions as well
Staphylococcus
- Family: Micrococceae (consists of Gram-positive cocci, arranged as clusters)
- Genus: Staphylococcus
- Term "staphylococcus" derived from Greek: Staphyle = bunch of grapes, and Kokkos = berry, meaning bacteria occurring in grape-like clusters or berry
- Staphylococcus aureus is the most important human pathogen (Coagulase-Positive staphylococci)
- Other important human pathogens: coagulase-negative staphylococci (CNS), including Staphylococcus epidermidis, Staphylococcus saprophyticus, and Staphylococcus haemolyticus
Culture and Biochemical Properties
- Aerobes and facultative anaerobes
- Optimal temperature for growth: 37°C
- Optimal pH for growth: 7.5
- Colony characteristics:
- On Nutrient agar: golden yellow, opaque, smooth, and glistening surface, 1-2 mm in diameter
- On Blood agar: golden yellow colonies, surrounded by a clear zone of hemolysis (beta-hemolysis), especially when incubated in sheep or rabbit blood agar in an atmosphere of 20% CO2
- On MacConkey agar: smaller colonies than those on NA (0.1-0.5 mm), pink-colored due to lactose fermentation
- On Mannitol salt agar: S. aureus ferments mannitol, appearing as yellow colonies
- Biochemical properties:
- Catalase: positive
- Oxidase: negative
- Ferments: glucose, lactose, maltose, sucrose, and mannitol, with production of acid but no gas
Learn about the Staphylococcus family, including their characteristics, arrangements, and importance in human pathogens. Discover the differences between coagulase-positive and coagulase-negative staphylococci.
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