40 Questions
What is the characteristic coloration of the medium resulting from red blood cell lysis?
Chocolate-brown
Which bacterial pathogens require enriched medium for growth?
Neisseria gonorrhoeae and Haemophilus species
What is the purpose of Eosin Methylene Blue (EMB) agar?
To differentiate between lactose fermenters and non-fermenters
What type of colonies are typically produced by lactose-fermenting E. coli on EMB agar?
Flat, dark colonies with a green metallic sheen
What is the purpose of Mueller Hinton Agar (MHA)?
To perform routine susceptibility testing by the Kirby-Bauer disk diffusion technique
What does a smaller zone of inhibition (ZOI) indicate in the Kirby-Bauer disk diffusion technique?
Lower sensitivity to the antibiotic
What does the absence of a zone of inhibition (ZOI) indicate in the Kirby-Bauer disk diffusion technique?
The organism is resistant to the antibiotic
What is the name of the technique used with Mueller Hinton Agar (MHA) for susceptibility testing?
Kirby-Bauer disk diffusion technique
What type of medium is Eosin Methylene Blue (EMB) agar?
Differential medium
What is the purpose of red blood cell lysis in the preparation of the medium?
To give the medium a characteristic color
What is the primary location of Enterobacteriaceae species?
Intestine
What is the term for a part of an organ that appears to be separate in some way?
Lobe
Which of the following organisms ferment lactose?
E.coli
What is the purpose of enrichment medium in microbiology?
To support the growth of fastidious bacteria
What is the composition of blood agar?
Autoclaved basal media with 5% defibrinated mammalian blood
What is the purpose of heating the blood to 80°C in chocolate agar?
To lyse red blood cells
What is the term for resembling mucus?
Mucoid
What is the purpose of MacConkey agar?
To differentiate between lactose-fermenting and lactose-non-fermenting bacteria
Which of the following bacteria is a lactose-non-fermenting organism?
Salmonella
What is the function of NAD in chocolate agar?
To provide nutrients to fastidious bacteria
What is a pure culture?
A laboratory culture containing a single species of organism.
What is the purpose of using a solidification agent in solid and semi solid media?
To solidify the media.
What is the main difference between nutrient agar (NA) and nutrient broth (NB) culture?
NA contains a solidifying agent, while NB does not.
What is the purpose of the spread plate technique?
To isolate and enumerate microorganisms in a mixed culture.
What is the result of a single cell occupying an isolated portion of the agar surface?
A visible colony of similar cells.
What is the characteristic of semi solid media?
It contains a low amount of agar.
Why is agar used in solid and semi solid media?
Because it is a solidifying agent.
What is the main advantage of using solid media?
It is easier to isolate microorganisms.
What is broth culture?
Any type of liquid used to grow bacteria.
What is the result of spreading bacteria on the surface of a solid medium?
A visible colony of similar cells.
What is the primary objective of cultivating microorganisms?
To maintain viable populations under controlled laboratory environments
What type of medium is tryptic soy broth (TSB)?
All-purpose medium
What is the characteristic of enriched media?
Contains growth factors, vitamins, and other essential nutrients
What type of medium is brain heart infusion (BHI)?
Complex medium
What is the purpose of selective media?
To inhibit the growth of unwanted microorganisms
What is the characteristic of MacConkey agar?
Contains bile salts and crystal violet
What is the use of BHI broth in laboratory settings?
Food safety tests and antibiotic sensitivity tests
What is the characteristic of complex media?
Precise chemical composition is unknown
What is the difference between chemically defined and complex media?
Chemically defined media have a complete chemical composition, while complex media do not
What is the purpose of culturing microorganisms?
To maintain viable populations under controlled laboratory environments
Study Notes
Importance of Media for Culturing Microbes
- The primary objective of cultivating microorganisms is to maintain viable populations of these organisms under controlled laboratory environments.
- Cultivating microorganisms is a challenging process due to their highly specific nutritional and environmental requirements and the diversity of these requirements among different species.
Nutritional Requirements of Microbes
- All-purpose medium: Tryptic Soy Broth (TSB)
- Specialized media: used in the identification of bacteria and are supplemented with dyes, pH indicators, or antibiotics
- Enriched media: contains growth factors, vitamins, and other essential nutrients to promote the growth of fastidious organisms
- Chemically defined medium: complete chemical composition of a medium is known (e.g. EZ medium)
- Complex media: contain extracts and digests of yeasts, meat, or plants, and the precise chemical composition is not known (e.g. nutrient broth, TSB, Brain Heart Infusion (BHI))
Types of Media
- Selective medium: inhibits the growth of unwanted microorganisms and supports the growth of the organism of interest (e.g. MacConkey agar)
- Enrichment medium: general purpose enrichment agar that can nourish and support the growth of gram-positive as well as gram-negative bacteria (e.g. blood agar)
- Differential medium: distinguishes between different microorganisms based on their metabolic characteristics (e.g. Eosin Methylene Blue (EMB) agar)
MacConkey Agar
- Contains bile salts and crystal violet, which interfere with the growth of many gram-positive bacteria and favor the growth of gram-negative bacteria, particularly the Enterobacteriaceae
- Lactose-fermenting organisms (e.g. E. coli) grow as pink to red colonies with or without a zone of precipitated bile
- Lactose-non-fermenting organisms (e.g. Salmonella, Shigella) form colorless or clear colonies
Blood Agar
- Enriched medium that supports the growth of fastidious bacteria and inhibits the growth of some bacteria like Neisseria and Haemophilus
- Contains 5% defibrinated mammalian blood (e.g. horse, sheep, human) added to the autoclaved basal media (TSA or Columbia Agar)
Chocolate Agar
- Enriched growth medium used for the isolation of pathogenic bacteria
- Nonselective, enriched growth medium that supports the growth of fastidious bacteria
- Contains red blood cells that have been lysed by slowly heating to 80°C, releasing intracellular nutrients
Obtaining Pure Culture
- A pure culture is a laboratory culture containing a single species of organism
- Obtained by transferring a small sample into new, sterile growth medium in such a manner as to disperse the individual cells across the medium surface or by thinning the sample many fold before inoculating the new medium
- Can be accomplished by spreading bacteria on the surface of a solid medium so that a single cell occupies an isolated portion of the agar surface
Solid vs. Semi-Solid vs. Liquid Media
- Solid media: contains a solidification agent (e.g. agar) and is used for the growth of microorganisms
- Semi-solid media (deep culture): prepared with a lower concentration of agar (0.2 to 0.5%) to observe motility of bacteria
- Liquid media (broth culture): a liquid used to grow bacteria, does not contain a solidification agent
Spread Plate Technique
- A method of isolation and enumeration of microorganisms in a mixed culture
- Distributes microorganisms evenly and makes it easier to quantify bacteria in a solution
This quiz covers the importance of media for culturing microorganisms, methods of obtaining pure cultures, and types of media used for bacterial growth.
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