Study "Principles of Traditional Cultivation Types of bacteria by n", a flashcard deck on FORKSAI.
What is the primary purpose of cultivation in microbiology?
Cultivation is the process of growing microorganisms in culture. Its main purpose is to meet the nutritional and environmental requirements of bacteria to allow them to grow, be isolated, and subsequently identified for diagnostic and susceptibility testing.
Differentiate between fastidious and non-fastidious bacteria based on their nutritional requirements.
Fastidious bacteria have complex or extensive nutritional requirements, meaning their culture media must be supplemented with items like vitamins, antibiotics, sugars, and inhibitors. Non-fastidious bacteria, in contrast, have basic nutritional requirements and can grow on simpler media.
Explain the difference between broth and agar as phases of culture media.
Broth is a liquid culture medium where nutrients are dissolved in water, appearing clear to turbid depending on bacterial presence. Agar is a solid culture medium that includes a solidifying agent, typically agarose, which melts at ≥95°C and resolidifies at <50°C, forming a stable gel.
What is the function of supportive (nutritive) media, and provide an example?
Supportive media are designed to support the growth of most non-fastidious organisms by providing general nutrients. An example is tryptic soy agar or nutrient agar plates for bacteria, or Sabouraud's dextrose agar for fungi.
How do enriched media differ from supportive media, and why are they used?
Enriched media are supportive media with added nutrient supplements to facilitate the growth of fastidious microbes. They are used when no organisms grow on solid media after initial specimen inoculation, providing additional nutrients like L-cysteine for specific bacteria such as Legionella pneumophila.
What is the primary role of selective media in bacterial cultivation?
Selective media permit the growth of certain bacteria while inhibiting others, often by incorporating inhibitory agents like dyes, bile salts, alcohols, acids, or antibiotics. This prevents the overgrowth of normal microbiota, allowing target organisms to be isolated.
Describe the characteristics of beta hemolysis observed on Sheep's Blood Agar (SBA).
Beta hemolysis is characterized by the complete clearing of red blood cells around a bacterial colony on Sheep's Blood Agar. This results in the medium changing from red to clear or yellow, indicating complete lysis of the red blood cells.
What specific components are released from lysed red blood cells in Chocolate Agar (CAP), and which organisms benefit from them?
When red blood cells are lysed in Chocolate Agar, hemin ('X' factor) and NAD ('V' factor) are released. These factors are essential for the growth of fastidious organisms such as N. gonorrhoeae and Haemophilus spp., which cannot grow on standard sheep blood agar.
What is the purpose of colistin and nalidixic acid in Columbia CNA with Blood agar?
In Columbia CNA with Blood agar, colistin and nalidixic acid are inhibitory agents. Colistin disrupts the cell membranes of gram-negative organisms, while nalidixic acid blocks DNA replication in susceptible organisms, effectively suppressing the growth of most gram-negative bacteria and allowing gram-positive bacteria to grow.
Which pH indicator is used in MacConkey Agar, and what color indicates lactose fermentation?
MacConkey Agar uses neutral red as its pH indicator. Lactose fermenting organisms will produce acid, lowering the pH and causing the colonies to appear pink to dark pink.