Examination
1
Explain how you would use the Hurdles or Barrier concept to ensure the safety and shelf-life
of a new food product you are developing?
Define water activity
Discuss the relationship between water activity and percent moisture as
water is added to rehydrate a food. Include as part of your answer an explanation of the
relationship between water activity and the safety and wholesomeness of the food. A properly
labelled figure must be included as part of your answer.
Describe what happens to bacteria in a food when the water activity is changed from 0.998 to 0.945 and why some bacteria can survive and other die.
(10 points) Describe why Staphylococcus aureus can survive and grow but Pseudomonas fluorescens cannot when each is transferred from a broth with a water activity of 0.98 to a broth with a water activity of 0.90.
Describe two types of microbial activity which influences the wholesomenes
and/or safety of foods.
Describe what you believe are the main function(s) and goal(s) of food microbiologists?
How do bacteria reproduce?
Draw the growth curves you would expect to obtain for the growth of Staphylococcus aureus in a broth at 12C and 35C. Label each curves.
What is the most common bacterial cause of foodborne illness in the United States?
What are the two most common causes of a foodborne outbreak.
Where do most incidences of foodborne illness occur?
Define the following terms:
Take Home Question (20 points)
You have been hired to develop a new pasta sauce for the "Wildcat" Food Company. This
product is to have a 14-day shelf-life at 10C, which means that the pathogen of concern must
not reach hazardous levels for 21-days.
What is the minimum salt concentration and pH value necessary to achieve this shelf-life under
aerobic conditions for Salmonella typhimurium at 10C. The initial population is
50/gram and the level of concern is 300,000/g.
Justify your answer by giving the generation time, lag phase duration and time for
microorganism to reach level of concern.
Salt Concentration =
pH =
Generation Time =
Lag Phase Duration =
Time To Reach Level of Concern =
BONUS QUESTION (15 points)
Determine the number of generations, generation time and growth rate that occurred during the logarithmic phase of growth under the following conditions. Show all calculations.
At 8 a.m Monday, September 18, you inoculate a broth with Staphylococcus aureus (1500 cells/ml) and incubated the culture at 35C. At 10:30 a.m. when the organisms entered its logarithmic phase of growth the population was 3120 cells/ml. The population was 3,250,000/ml when the end of the logarithmic phase of growth was reached at 8:15 p.m. that evening.
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Contents.
Examination
2
Pathogen with the lowest water activity for growth:
All or some strains of this species are coagulase-positive:
Species in this genus tend to be radiation resistant:
Genus which contains species capable of oxidizing ethanol to acetic acid:
Species presently creating a health problem due to transovarian contamination of eggs:
Species responsible for "eyes" in Swiss cheese:
Species which may produce both a heat-stable and heat-labile enterotoxin:
Psychrotrophic foodborne pathogen:
Gram-positive rod that is an intercellular parasite
Leuconostoc mesenteroides subsp. cremoris can utilize citrate only
when the pH
is:
Species considered to be oxidase-positive:
Species which produces non-diffusible pigment:
Present times and temperatures used for pasteurization of milk is based on the:
Only Kanagawa-positive strains of this pathogen are considered to cause foodborne
illness:
Species in this genus are acid-alcohol fast during some stage of its growth
cycle:
Luciferase involved in the emission of a light or bioluminescent in species in this
genus:
Gram-positive rod which causes foodborne infection:
Gram-positive cocci used in the manufacture of yogurt:
Pseudomonas aeruginosa produces the following pigment (s):
Species which may produce a heat-stable enterotoxin:
Species which produces a crystal protein used as a bioinsecticide:
Species which shows a characteristic darting or corkscrew motion when viewed under the phase contrast microscope:
Species considered to be a human pathogen:
Gram-positive, catalase-negative rod:
Species responsible for yersiniosis:
"Citric Acid Fermenter" or species capable of producing diacetyl from citrate:
Species responsible for thermophilic flat-sour defect in canned foods:
Species which may release a toxin during sporulation in the intestinal tract:
Lowest temperature reported for growth of proteolytic strains of Clostridium
botulinum :
Species used in the manufacture of some surface-ripened cheeses:
Species used to determine time-temperature requirements for processing canned foods
with pH above 4.5:
Gram-positive species which can establish in the intestinal tract of humans:
Species considered to be the most heat resistant sporeformer found in foods:
Irreversible step in spore outgrowth:
Foodborne illness due to a neurotoxin produced in the food:
Species used in the manufacture of fermented meats:
Test used to distinguish members of the Family Enterobacteriaceae from
members
of
the Family Pseudomonadaceae :
Anaerobic species that may produce an enterotoxin:
Species that has been reported to causes diarrhea in humans equal to or exceeding that
caused by salmonellae and shigellae:
Species Which May Produce a Fatal Illness to Persons with High Serum Iron Levels:
Requires a Special Atmosphere (5% Oxygen, 10% Carbon Dioxide & 85% Nitrogen for its
Isolation:
Foodborne Pathogen(s) Capable of Growth below 5C (Psychrotrophic):
Pathogen that is motile at 25C, not motile at 37C
For each of the following give a characteristic for each organism
which could be used to differentiate it from the paired organism. For ONE of the organisms
in each pair, state where or why it might be important in the food industry.
Example
Clostridium thermosaccharolyticum
Desulfotomaculum nigrificans
Clostridium perfringens
Bacillus cereus
Escherichia coli
Salmonella typhimurium
Gluconobacter oxydans
Acetobacter aceti
Pseudomonas fluorescens
Pseudomonas aeruginosa
Lactococcus lactis subsp. lactis
Leuconostoc mesenteroides subsp. cremoris
Describe the carrier states that may occur when foods containing certain pathogenic
gram-negative enteric bacteria are consumed by humans.
Why are human carriers of concern to the food industry?
Describe the pathogenic mechanisms involved in foodborne illness for the following:
Describe the inhibition of spores in cured meat products.
What would you tell the public regarding raw foods of animal and marine origin and their role
in helping to control foodborne illness?
Why is botulism a greater potential hazard in packaged raw fish than in packaged raw
meat?
BONUS QUESTION (20 points)
Species
Mold Species That Can Grow at Low pH and in Reduced Oxygen Tension in Canned
Fruit and Fruit Drinks::
Genus of yeast which reproduces by fission:
Genus of mold reported to contain species capable of producing mycotoxins:
Yeast species which may show resistance to some preservatives (benzoic acid, sulfur dioxide,
acetic acid) used in foods:
Considered to be one of the 10 species of yeasts responsible for spoilage of foods processed
and packaged under GMP:
Species which has lowest requirement for available water of any microorganism
known:
Mold species which produces a rennet substitute used in cheese making:
Mold species which forms very heat resistant ascospores:
Critical temperature in thermal processing of animal products to ensure destruction of
viruses:
All stages of the life cycle of this foodborne pathogen occurs within a host:
Protozoan illness which may be associated with cysts in meat and of concern to pregnant
women.
Mold Species Involved in Flavor Characteristics of Surface Ripened Cheeses:
Type of Reproduction Observed for Teleomorphic Molds:
Genus of mold reported to contain species capable of producing aflatoxins:
Genus of yeast which reproduces by fission:
Two viruses most commonly implicated in foodborne viral illnesses.
Fishborne illness characterized by both gastrointestinal and neurologic symptoms.
Differentiate the following types of reproduction observed for fungi and give a genus for
each type. A properly labelled figure is acceptable.
Name and describe seven (7) types of reproduction observed for teleomorphic and
anamorphic fungi and give a genus for each type. A properly labelled figure is
acceptable.
Discuss the composition of the microflora you would expect to observe for the inner tissue
and external surface of beef carcass for the following conditions:
Describe four (4) microbial interrelationships you would expect to observe in foods and give
one (1) example for each.
Describe the three (3) principles involved in the various methods used for the preservation of
foods and give one (1) example how each principle can be achieved.
As a food microbiologist, how would you explain to the average consumer what determines
the wholesomeness (fitness) of a food?
Define or Explain the Following in Relationship to Their Importance in the Food Industry
Why Is Water That Is Safe to Consume from the Public Health Standpoint Not Always
Suitable for Use in Food Manufacturing Plants?
Define biofilms and indicate why they are a concern to the food industry.
You have been working in the Quality Control lab at Wildcat Foods for a month when
you noticed a dramatic increase in the incidence of thermophilic incubator spoilage of
canned peas produced by the company.
Describe the Sequence of Events That Occur When a Bacteriophage and Susceptible
Bacterium Meet.
Describe the steps you would use to determine the cause of the increased spoilage. Include
in your discussion the procedure(s) you would use to determine the D-value and z-value of
the spoilage organism.
BONUS QUESTION
A broth culture of Staphylococcus aureus is heated at 57.6C for 22 minutes. Describe,
including media you would use, how you would determine the following:
Describe How You Would Determine the Dr Value of a Bacteria You Isolated.
Gram-positive, Catalase-negative Rod:
The Color of Fecal Coliform Colonies on Membrane Filters:
The Reason(s) Solid Samples must Be Diluted Before Being Enumerated:
When Determining Coliforms by Membrane Filtration, Results Should Be Based on the
Sample Volume Which Gives:
Bacteria That Reduce TTC Produce Colonies That Are:
Samples Should Be Diluted So That Agar Plates Used to Determine Coliforms
Contain:
Chemical Used to Neutralize Chlorine in Water Prior to Microbiological Testing:
Incubation Temperature Used to Distinguish Fecal from Non-fecal Coliforms:
Considered a Microbiological Criteria:
Preservative With Antimicrobial Activity at pH 7:
Sorbate Would Be Most Effective Against:
A Chemical Cannot Be Used as a Food Additive If It:
After 0.1 ml of Sample Has Been Dispersed to a Petri Dish, the Pipette Should Be Touched to
a Dry Area on the Plate:
Considered the Most Heat Resistant Pathogen of Concern in Milk:
Species Responsible for the Characteristic Flavor and Appearance of Blue-veined
Cheese:
The pH of Media Should Be Determined at:
Temperature That Agar Media Should Be Temperated at Before Being Used to Pour
Plates:
Samples Should Be Diluted So That Plates Used to Determine the Aerobic Counts
Contain:
Propionates Are Effective Against:
More Sulfide Dioxide Would Be Present At:
How Long Would it Take to Reduce 109 Bacillus stearothermophilus to 1 at
121C. Dr = 5.8 min):
Germicidal Lamps Used in Ultraviolet Treatment of Foods Emit Radiation at:
Preservation of Foods by Low Temperature Is Based on:
Blanching Fruits and Vegetables Will Result In:
Undesirable Characteristic(s) for a Chemical Preservative:
Temperature Range Used to Store Most Perishable Foods:
Generally Considered to Result from Freezing:
Temperature Range Where Decline in Microbial Population During Freezing or Storage
Is the Greatest:
The D Value for Staphylococcus aureus Would be Higher in:
Agar contact method used in a laboratory experiment to determine the sanitary condition of
food contact equipment:
Matching Question.
Indicate which incubation condition would be the best for the isolation of bacteria in the
following genera. Select only the one best condition.
____ 1. Bacteroides
A. Aerobic
Indicate the Procedure (Whether Pour Plates or Surface Spread Plates), Medium (Media),
and Incubation Conditions (Temperature and Time) That You Would Used for the
Following Enumerations. Spell out the Name of the Media the First Time Used, Then
You Can Use its Abbreviation.
Number of Coliforms in Milk.
Percentage of Coagulase-positive Staphylococcus aureus in Lemon-cream
Pie.
List the Preservative for Each of the Following:
Name the Microorganism or the Illness for Each of the Following:
Define or Explain the Following in Relationship to Their Importance in the Food
Industry
List in Order the 12 Steps You Would Used to Establish a HACCP Program in a
Plant.
You Discovers That Your Freezer Containing Poultry, Beef, Fruit and Vegetables Has Been
off for Some Time. What Would You Do with the Items in Their Freezer? Give Reason(s)
for Your Actions.
Discuss the differences that slow and fast freezing have on microorganisms
BONUS QUESTION
A Broth Culture of Staphylococcus aureus Is Heated at 57.6C for 22 Minutes.
Describe, Including Media You Would Use, How You Would Determine the
Following:
The identification markings on ten (10) tubes containing pure cultures of the species listed
below became illegible during storage. Using the gram stain and a maximum of six (6)
additional tests or procedures, outline how you would determine the identity of the culture in
each tube. Give reactions for each test or procedure used. A properly labelled flow diagram,
containing tests or procedures and results, is acceptable.
Bacillus cereus
Clostridium perfringens
Leuconostoc mesenteroides subsp. cremoris
Lactobacillus acidophilus
Lactobacillus viridescens
Micrococcus luteus
Staphylococcus aureus
Lactococcus lactis subsp. cremoris
Proteus vulgaris
Pseudomonas putida
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Contents.
Multiple Choice Questions. Circle ALL correct answers. If the correct answer
is NONE OF ABOVE, the correct answer with the correct spelling must be given in order to
get credit for the question. Examination
3
Give a microbial species or microbial group that could be involved in the following (Species
or group must be spelled correctly to obtain credit):
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Contents.
Multiple Choice Questions. Circle ALL Correct Answers. If the Correct
Answer Is NONE OF ABOVE, the Correct Answer must Be Given in Order to Get Credit
for the Question. Final
Examination
___ 2. Campylobacter
____ 3. Clostridium
____ 4. Lactobacillus
____ 5. Pseudomonas
____ 6. Selenomonas
B. Anaerobic Gas Pak jar
C. Carbon Dioxide (CO2) Gas Pak
D. Glove Box
E. 5% O2, 10% CO2, 85% N2
F. Roll tube
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Contents.
RETURN TO:
FSC 530 Food Microbiology Home Page
Food Science Home Page
Department of
Animal Sciences Home Page
College of Agriculture Home Page
University of Kentucky Home Page
URL
http://www.uky.edu/Agriculture/FoodScience/FSC530/exams.html