MCB101 Exam III

Flashcards Are For An Introductory Microbiology Lab. They Cover Multiple Topics Form Different Kinds Of Bacteria To Different Biochemical Tests, Etc. Covers Labs 15-19.

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Side ASide B
microorganisms that cause illness or disease
3 places foodborne illnesses come from
presence of pathogens in IT, the production of a toxin by a path. in the gut, ingestion of a toxin from growth on food
most foodborne illness result in ____, but can be especially dangerous in _____.
diarrhea children, elderly and immunocompromised
found in animal intestines especially poultry, transmitted in uncooked meat
camplyobacter jejuni
an infection of camplyobacter jejuni causes:
fever, headache, muscle pain, diarrhea, abdominal pain and nausea
found in intestines of birds or mammals, transmitted in undercooked eggs,meat, and milk
a salmonells infection causes:
fever, chills, aches, abdominal pain, and may be serious if it spreads to blood
found in the intestines of mammals(cattle)
Escherichia coli
an e.coli infection causes:
diarrhea, dysentery, kidney failure, blindness, paralysis, death
most foodborne illnesses are caused by:
fecal-oral cycle pathogens
the USDA's standard for maximum permissible number of bacterial cells in hamburger is:10
10^7 cells/gram
hamburger should be cooked to:
160 degrees Farenheit
in the hamburger contamination lab, what type of medium did we use?
3M petrifilm cultures to get a total aerobic bacteria count and a coliform count
What volume of liquid is used to inoculate a 3M Petrifilm culture?
1.0 ml
A 0.1ml aliquot of a 10-2 dilution of the sample gives 90 colonis.What is the concentration of coliform bacteria?
9.0 x 10^2
On a 3M Petrifilm culture for E.coli, a colony of a fecal coliform appears:
blue and is associated with gas bubbles
What is the term for microorganisms that can grow and cause food spoilage in the refrigerator?
What type of microorganism is Penicillium?
fungus (mold)
The food preservative sodium nitrite is:
an inhibitor of pyruvate-ferrodoxin oxidoreductase
Nitrites are added to meat because it gives meat a pink color and inhibits:
Clostridium botulinum
How do propionate and benzoate prevent microbial growth?
They increase the proton concentration of the cytoplasm in microbes.
Which one of the following substances is not classified as a disinfectant? bleach, alcohol, phenol, tetracylcine
An antiseptic is
an antimicrobial substance that is used to kill or inhibit microorganisms on the skin
chemical disinfectants are more lethal to bacteria at ______
higher concentrations
____ was used as a disinfectant in hospitals for many years.
The Snyder Test is used to:
check for high numbers of glucose-fermenting, acid-tolerant bacteria in saliva.
Snyder Test Agar will turn fully yellow only if the pH drops below:
In ethanol fermentation yeast produce one molecule of ___ for every molecule of ethanol they make.
Both ethanol and lactic acid can inhibit:
the growth of undesirable microorganisms in food products.
The predominant sugar found in grape juice is:
The production of yogurt is an example of:
a microbial succession that primarily involves two species of bacteria.
process of yogurt production:
scald milk to 80C, allow to cool below 65C, add commercial yogurt, incubate at 43C
if 100 grams of sugar is converted to ethanol in 100% efficient reaction, the yeast produces:
51 grams of ethanol and 49 grams of carbon dioxide
Yogurt production primarily involves:
the fermentation of milk sugar,lactose, to produce lactic acid.
What two bacteria are used to make yogurt?
Lactobacillus bulgaricus and Streptococcus thermophilus
nitrite converted to nitrate is:
an oxidation reaction
ammonia converted to nitrite is:
an oxidation reaction
nitrate converted to elemental nitrogen (N2) is:
a reduction reaction
elemental nitrogen (N2) converted to ammonia is:
a reduction reaction
The oxidation of ammonia to nitrate is called:
Nitrosococcus bacteria can produce energy by oxidizing:
ammonia to nitrate
Some strains of Pseudomonas bacteria can reduce:
nitrates to nitrogen gas
The enzyme urease breaks down urea to:
ammonia and CO2
The breakdown of amino acids and other nitrogen-containing organic compounds to release ammonia is called:
Trommsdorf reagents produce a ____ color when they react with nitrite (NO2-).
dark blue inky
Trommsdorf reagent ___ can burn your skin or cause holes to appear in your clothing.
For the nitrate reductase test, a color change to blue after the addition of zinc indicates a:
NEGATIVE test result (nitrate was not reduced by the bacteria).
For the ammonia oxidation test, a color change to blue after addition of zinc indicates a:
POSITIVE test. (Bacteria oxidized the ammonia completely to nitrate.)
Trommsdorf reagents do not react with:
Nitrification is also called:
ammonia oxidation
Nitrification is a two-step process. ____ carries out the first step while ____ carries out the second step.
Nitrosomonas,Nitrosococcus, & Nitrosospirina/ nitrobacter,nitrosococcus, and nitrospira
Nitrification is an:
aerobic process
nitrification ____ energy (ATP)
Denitrification is an:
anaerobic process
Mammals excrete excess nitrogen primarily in the form of:
most bacteria and aquatic animals excrete excess nitrogen in the form of:
The main carbon source in the ammonia broth used in Experiment 19C is:
The carbon source in nitrate broth (Ex. 19b) is:
a mixture of organic compounds
The only organisms that can convert elemental nitrogen (N2) to organic forms are:
certain prokaryotes
why is hamburger especially subject to contamination by pathogens?
the chopping process mixes anny surface bacteria that are present as well as air in with the meat
name the bacteria that cause foodborne illness:
camplyobacter jejuni, clostridium botulinum, clostridium perfringens, e.coli, salmonella, listeria monocytogenes, shigella, staph. aureus
for hambuger contamination lab, what tubes did you use for the uncooked meat and what were they labeled?
three 9.9ml and one 9.0ml tubes of saline, 10^-3, 10^-5, 10^-7, and 10^-6
in hamburger contamination lab, what tube did you use for the 120 degree meat and the 160 degree meat?
9.9ml saline tube for the 10^-3 120 degree, and 9.0ml saline tube for the 10^-2 160 degree
at what temperature do you incubate the 3M petrifilms?
37 degree C
how do you calculate the total number of cell/gram of meat?
dilution facter X number of colonies
spoilage from microorganisms causes a loss of up to ___% of all food grown for human consumption
small organic acids from carbohydrates can cause food to tast ____.
longer chain fatty acids made ffrom the breakdown of fats can cause a food to taste ____.
the breakdown of proteins can yield ammonia, amines, and hydrogen sulfide that make food ____.
physical methods for controlling microbial growth on food:
heat (dry,moist, or pasteurization), filtration, desiccation, osmotic pressure and radiation (ionizing and nonionizing)
sulfer-based preservatives
when looking at the diameter of a mold colony:
the smaller the diameter, the more effective the preservative was
a paper disk is soaked with a substance and placed on the surface of an agar medium that has been uniformly inoculated with a microorganism
disk diffusion test
factors that affect the size of the zone of inhibition observed in a disk diffusion test
concen. of the antimicrobial agent, substance being tested,species of microorganism tested,rate of diffusion of substance through agar, conditions
what fermentable sugar and pH indicator dye are in the Snyder test agar?
dextrose (glucose), bromcresol green
difference between snyder test agar and OF-glucose agar
starting pH of snyder is more acidic (4.8), snyder will not turn yellow until it reaches a much lower pH
from of anaerobic metabolism in which the terminal electron acceptor, or oxidizing agent, is an organic compound.
process in wine production where dead yeast cells settle to bottom and are transferred to different tank.
what does scalding the milk do in yogurt production?
it will kill any contaminating bacteria, drive off oxygen to enhance anaerobic conditions, and reduce water content
how do you calculate to mass of alcohol produced
multiply the mass of carbon dioxide lost by 1.045
the conversion of atmospheric nitrogen (N2) to ammonia is caled:
nitrogen fixation
use of nitrogen or ammonia by incorporating into amino acids or proteins, opposite of mineralization
nitrogen assimilation
process of reducing nitrate to ammonia except that nitrogen is not lost from the soil
assimilatory nitrate reduction
nitrogen fixation is catalyzed by the enzyme:
chemistry of trommsdorf reagents
sulfuric acid in II react with nitrite to produce nitrous acid which then reacts w/ iodide to form iodine, starch in I from blue complex with iodine
a yellow-orange result for urea broth indicates:
a negative result, does not degrade urea to ammonia
a bright pinkish-red result for urea broth indicates:
a positive result, degrades urea to ammonia
for hamburger lab, TA prepares the 10^-1 sample by:
mixing 10G of hamburger with 90ml of sterile saline
what organism was used to contaminate hamburger?
for the aerobic plate count petrifilms, you use the ____ side of the spreader to distribute the sample
for the viable plate count, what volume do you spread on the petri plates?
to estimate the number of colonies on aerobic petrifilms:
count the number of colonies in 2 squares, average them, and multiply by 20
how many petri plates do you use for ex. 16 (food preservatives)?
how much 2% propionate stock solution should you add tot he petri dish in order to get a final concentration of 0.3%?
how long do you wait after mixing agar w/ preservatives before moving or inoculating the plate?
15 to 20 minutes, then inoculate
what technique should be used to inoculate potato dextrose agar w/ penicillium?
place a drop in the center of the plate and allow to dry
penicillin and tetracycline are:
alcohol, tincture of iodine, and bactine are:
for ex.17 you prepare two plates of:
s.epidermis and e.coli
the negative control for ex. 17 is:
a drop of water
for ex. 17, how much solution do you add to the plates to test?
5 microliters
for the snyder test, what do you do to distribute sample throughout tube?
roll gently between hands
snyder test is incubated for:
more than 25 hours
sugar used in agar medium for growing lactic acid:
sugar used in PDA, the agar for growing yeasts, is:
how much sugar is present in 8oz. of Welch's grape juice?
40 grams
how much sugar do you add to the grape juice?
30 grams
how much warm water do you use to activate the yeast?
how much yeast do you put into the grape juice?
2-3 grams
on day 1 of wine production, you take a sterile loop of the mixture and:
streak a PDA plate
what days do you check pH for wine production?
day 1 and 5
what days do you calculate ethanol production for wine ex.?
day 5
what days do you smell the mixture to detect ethanol production in wine?
days 2,3,4 and 5
what days do you observe the bottle of wine to detect gas?
days 2,3,4 and 5
metallic zinc can reduce nitrate to:
when setting up urease test in 19a, you inoculate urea broth with:
4 loopfuls
used in 19b to inoculate both nitrate and PBE broths but not in 19a:
pseudomonas aeuignosa
show a positive result in urease test:
proteus vulgaris
used to inoculate 2 tubes of ammonia broth in 19c, one gets air and one does not:
shows a negative result in the urease test:
serratia marcescens
linear plots plot:
Log AU vs. time
semi-log plots plot:
AU vs. time
takes over when the pH drops below 5 in yogurt production:
lactobacillus bulgaricus
gros most udring the late stage of yogurt production:
lactobacillus bulgaricus
glutamic acid is made from alpha-keto-glutarate plus ammonia:
nitrogen assimilation

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