Lab Material Flashcards
BPA
Baird-Parker Agar
isolation of Staph aureus
composition of BPA:
sodium pyruvate (protect damaged cells) egg yolk (diagnostic agent)
NA
Nutrient Agar
Nonspecific
SDA
Sabouraud Dextrose Agar
dermatophytes/fungi/yeast
Conditions of SDA:
acidic
Where does the term “Gram-stain” come from?
Hans Christian Gram (microbiologist)
Order of reagents for performing a Gram stain:
Crystal violet
Iodine
Decolorizer
Safranin
What does a Gram stain indicate? How?
Gram-positive vs Gram-negative (presence of cell wall)
- positive: cell wall will retain crystal violet (purple)
- negative: no cell wall, stained with safranin (pink)
A HHD agar showing colonies surrounded by yellow indicates what type of bacteria? Why?
homofermentative LAB (lactobacilli) produce more acid -> bromocrescol green becomes yellow
What color will streptococci colonies be surrounded by on a HHD agar? Why?
blue-green
produce less acid, bromocresol green stays green
How could we safely reduce the salt content of sauerkraut to 1%?
Use starter culture (L. mesenteroides) to bring down pH safely while making flavor compounds
How does the bacterial population change in the sauerkraut process?
beginning: heterofermentative (make flavors)
2-3 days: homofermentative (acid tolerant) take over
end conc: 10^8 to 10^9
What is the advantage of OGYE vs SDA? Why is this?
gives higher yeast counts
uses antibiotic (oxytetracycline) to kill competition instead of low pH (stresses yeast)
The main organic acid in grape wine is: ____. The main organic acid in strawberry wine is: _____.
tartaric acid
citric acid
What are the uses for each component in OGYE agar?
oxytetracycline: kill competing bacteria
glucose: sugar as food
yeast extract: provide peptides/AA for growth
agar: set gel
What are the purposes of the agents in ADPA?
tartic acid: lower pH (inhibit most microbes)
Dextrose: growth stimulant
Potato infusion: nutrients
What are the purposes of the agents in ADPA?
tartic acid: lower pH (inhibit most microbes)
Dextrose: growth stimulant
Potato infusion: nutrients
What agar is recommended for isolation of Listeria monocytogenes? What is the appearance of the colonies?
PALCAM Agar
Listeria will be grey-green, with black precipitate
What are the agents in PALCAM Agar that make it highly selective?
LiCl
ceftazidime,
polymixin B
Acryflavine HCl
Mannitol fermenting microbes on a PALCAM agar will appear:
with yellow halo/yellow colony
What does the abbreviation ‘spp.” mean?
referring to subspecies
What medium is used to dilute bacterial solutions?
0.1% peptone saline
What is the catalase test?
drop H2O2 onto colony on slide - watch for bubbles
bubbles indicate CATALASE POSITIVE (has catalase enzyme)
Pasteurized milk is heated at ___ for ____.
Raw milk is milk that has been kept below ____.
63C, 30 min +
40C
What agar is used to differentiate between homofermentative and heterofermentative LAB? What is the important ingredient?
HHD agar Bromocresol green (indicator)
What is the appearance of heterofermentative bacteria on HHD agar? Why?
colorless colonies surrounded by various colors
produce less acid -> less strong of a color change
What is the carb source in HHD media?
fructose
Why is it important to monitor sugar content in maple syrup?
If not sufficiently concentrated, spoilage will occur
Can mold grow on maple syrup?
Yes; if not sufficiently heat treated, or stored too long after opening (common problem)
The agar commonly used for Kirby-Bauer tests: ______.
Why? (3)
Mueller Hinton Agar
- “loose” agar - allows for antibiotic to easily diffuse, giving clear zone of inhibition
- nonselective (can use for many diff. organisms)
- starch will absorb toxins from bacteria (prevent from interfering with antibiotic action)
What does TSA contain? (2)
soy/casein peptones (organic nitrogen)
NaCl (or other salt): maintain osmotic equilibrium or select for halotolerance
What is TSA used for?
general growth media, cultivation/storage/maintenence/transport of pure cultures
According to disc diffusion test inhibition zones, bacteria are classified as:
resistant, intermediate, sensitive
The greater the zone of inhibition diameter, the more _____ the microbe
sensitive
Canned foods are classified based on _____.
acidity
What is TSM and what is it used for? What is done to further acidify the media?
tomato serum media
cultivate/enumerate Lactobacilli
Can adjust to pH 5.1 by adding 1 mL/100mL 10% lactic acid
What is PCA used for?
Plate count agar: nonselective, total viable bacteria growth
What is DTB and what is it used for?
Dextrose Tryptone Broth
cultivate/enumerate spoilage organisms from low/med acid canned food
How much of the sample should be added to 10 mL Dextrose Tryptone broth?
2g of food sample
What is the recommended procedure/mediums for examining spoilage microbes in low/med acid canned food?
aerobic culture in DTB, at 35 and 55C
anaerobic culture in Liver Broth, at 37 and 55C
What is liver broth? what growth does it support?
liquid with liver particles
saccharolytic/putrefactive; mesophilic/thermophilic;
anaerobic (agar plug)
What is the procedure/media for examining spoilage microbes in high acid canned food?
aerobic culture in tomato serum broth, transfer to DTA or acidified Sab Agar, at 25, 37, 55C
anaerobic culture in tomato serum broth (with agar plug); incubate at 25, 37, 55C
Describe the color change in DTB and why it occurs:
purple -> yellow
due to microbes consuming dextrose and making acid (Bacillus and other “flat sour” organisms)
What signifies bacterial growth in anaerobic tubes?
turbidity
rising of agar plug (gas production)
A 0.5 MacFarland standard is equivalent to:
10^8 inoculum
