question
Why are some microorganisms called "normal microbiota"?
answer
Because they are microorganisms that colonize a host without causing disease; also called normal flora.
question
How does the host usually benefit from normal microbiota?
answer
By preventing the overgrowth of harmful microorganisms. This phenomenon is called microbial antagonism, or competitive exclusion. They compete for attachment against pathogens, producing acid and producing Bacteriocins (bacterial toxins that prevent growth of other bacteria "kill invading bacteria")
question
Define a differential medium. What is its purpose?
answer
Makes it easier to distinguish colonies of the desired organism from other colonies growing on the same plate because they grow with different characteristics
question
Define a selective medium. What is its purpose?
answer
Contains chemicals that allow/encourage some types of bacteria to grow, while inhibiting/suppressing the growth of other types.
question
Why is MacConkey agar considered both selective and differential?
answer
- Inhibits the growth of Gram positive organisms due to the presence of crystal violet, so this medium is selective for gram-negative bacteria.
- It can distinguish between groups of bacteria on the basis of a color change reaction
- It can distinguish between groups of bacteria on the basis of a color change reaction
question
Why is EMB agar considered both selective and differential?
answer
- The dyes Eosin and Methylene blue inhibit Gram positive organisms from growing, so this medium is selective for gram-negative bacteria.
- The medium differentiates based on the ability to ferment lactose (and/or sucrose.) Organisms that cannot ferment the sugars produce colorless colonies and those that ferment the sugars with some acid production produce pink or purple colonies, organisms that ferment the sugars and produce large amounts of acid form colonies with a green metallic sheen.
-This medium is commonly used to detect the presence of fecal coliforms (like E. coli)
- The medium differentiates based on the ability to ferment lactose (and/or sucrose.) Organisms that cannot ferment the sugars produce colorless colonies and those that ferment the sugars with some acid production produce pink or purple colonies, organisms that ferment the sugars and produce large amounts of acid form colonies with a green metallic sheen.
-This medium is commonly used to detect the presence of fecal coliforms (like E. coli)
question
Why is blood agar useful as a medium?
answer
Most pathogens grow well because its an enriched medium and differential for hemolysis
question
Why might people make a Gram stain directly from a clinical specimen?
answer
Allows for quicker assessment of possible antibiotics for treatment.
question
Why is aseptic technique important in the laboratory?
answer
To avoid contamination and avoids lab workers from potentially getting infected from the sample
question
Why is aseptic technique important in patient care?
answer
To minimize potential contamination of staff and other patients, and help contain the pathogen that cause the infection.
question
A patient has an abscess on their neck. Describe the procedures you could use to determine what organism is causing the abscess.
answer
You could obtain a sample from the patient and use Koch's postulates to help determine the particular pathogen causing the disease.
question
Blood agar
answer
Enriched and differential medium, 5-6% sheep blood, Most pathogens grow well; differential for hemolysis
question
Mannitol salt agar (MSA)
answer
Selective and differential medium, 7.5% NaCl, mannitol,
phenol red, Isolates Staphylococcus spp.
phenol red, Isolates Staphylococcus spp.
question
Chocolate agar
answer
Enriched medium, Cooked hemoglobin, Isolates Many fastidious pathogens grow well
question
Modified Thayer-Martin agar (MTM)
answer
Selective and enriched medium, Cooked hemoglobin,
antibiotics, Isolates Neisseria spp.
antibiotics, Isolates Neisseria spp.
question
MacConkey agar
answer
Selective and differential medium, Lactose, bile salts,
neutral red, crystal violet, Isolates Gram-negative enteric bacilli
neutral red, crystal violet, Isolates Gram-negative enteric bacilli
question
Eosin methylene blue agar (EMB)
answer
Selective and differential medium, Lactose, eosin,
methylene blue, Isolates Gram-negative enteric
bacilli
methylene blue, Isolates Gram-negative enteric
bacilli
question
Examining growth on EMB agar, how might you distinguish Escherichia coli from Enterobacter aerogenes?
answer
Through their colonies physical characteristics,
E. coli: metallic green color.
Enterobacter aerogenes: thick pink, mucoid color
E. coli: metallic green color.
Enterobacter aerogenes: thick pink, mucoid color
question
Examining growth on MacConkey agar, how might you distinguish Escherichia coli from Enterobacter aerogenes?
answer
E. coli: red color colonies surrounded by a fuzzy looking halo
Enterobacter aerogenes: Pink/Red color colonies that are glistening and mucoid
Enterobacter aerogenes: Pink/Red color colonies that are glistening and mucoid
question
Examining growth on EMB agar, how might you distinguish Escherichia coli from Staphylococcus aureus?
answer
E. coli: metallic green color.
Staphylococcus aureus: thick pink, mucoid color
Staphylococcus aureus: thick pink, mucoid color
question
How can you distinguish among the three UTI-causing pathogens on the HardyCHROM UTI plate?
answer
By, their growth and characteristics such as color and if they grew.
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