Answer all questions on the general answer sheet provided (IN PENCIL). Choose the most correct option.
1. Lipopolysaccharide of bacterial cell walls contains which of the following:
a. Lipid A
b. N-Acetylglucosamine
c. Peptidoglycan
d. Porins
e. N-Acetylmuramic acid
2. What organism was the subject of the Gruinard experiment?
a. Salmonella typhi
b. Clostridium botulinum
c. Clostridium tetani
d. Bacillus anthracis
e. Wingardium leviosa
3. Members of the same bacterial genus must have at least what percentage identity in rRNA sequence?
a. 70%
b. 97%
c. 95%
d. 93%
e. 63%
4. Which of the following are common genera of plant surface flora?
a. Bacillus
b. Erwinia
c. Cladosporium
d. Lactobacillus
e. All of the above
5. Normally meat surfaces should have approximately how many bacteria per cm2?
a. 101-102
b. 103-104
c. 104-105
d. 106-107
e.
Session 1, 2019 – FDS202 Page 3 of 12
6. If a bacterium has a specific growth rate (μ) of 0.2 h-1 what is the approximate generation time of this organism?
a. 20 mins
b. 30 mins
c. 120 mins
d. 180 mins
e. 220 mins
7. Which of the following is NOT an intrinsic factor of foods?
a. nutrients
b. growth factors
c. inhibitors
d. relative humidity
e. pH
8. The limit of water activity under which microorganisms generally don’t grow is?
a. 0.6
b. 0.9
c. 0.2
d. 0.8
e. 0.7
9. Redox potential of food is greatest under which of the following conditions?
a. High O2; Low pH
b. Low O2; Low pH
c. High O2; High pH
d. Low O2; High pH
e. Redox potential is not affected by O2 concentration and pH
10. Plasmids are primarily transferred between bacterial cells naturally by which of the following processes?
a. Conjugation
b. Transformation
c. Bacteriophage infection
d. Transposons
e. Telekinesis
11. Thermoduric psychrotrophic bacteria are:
a. often endospore forming and Gram positive
b. usually not present in raw milk
c. are easily killed by pasteurization
d. only grow well under high pressure
e. are never endospore forming, and usually Gram negative
Session 1, 2019 – FDS202 Page 4 of 12
12. The pH of fish flesh post-mortem is approximately:
a. 4.6 – 4.8
b. 5.4 – 5.5
c. 6.2 – 6.5
d. 7.5 – 7.8
e. 8.5 – 8.8
13. Spoilage of aerobically stored, chilled red meats (not plastic wrapped) is usually by:
a. Gram positive bacteria, such as Lactobacillus
b. Fungi, such as Botrytis cinerea
c. Gram negative bacteria, such as Pseudomonas species.
d. Strictly anaerobic bacteria
e. All of the above
14. HTST pasteurisation of fresh milk is generally:
a. 72°C for 10min
b. 121°C for 2-3sec
c. 65°C for 30min
d. 72°C for 15sec
e. 90°C for 1min
15. Most bacteria generally grow well between pH values of:
a. 2 – 4.5
b. 3 – 5
c. 4 – 5.5
d. 6 – 8
e. 8 – 9.5
16. Chopping or mincing meat will cause its Eh value to:
a. Slightly increase
b. Slightly decrease
c. Not change
d. Increase significantly and then later decrease with microbial growth
e. Decrease significantly and then later increase with microbial growth
17. Generally, the bacteria commonly associated with marine fish spoilage:
a. Are introduced by handling and storage
b. Are pyschrotrophic and can handle a range of sodium concentrations
c. Have a tolerance to high pressures
d. Are mesophilic
e. Produce extracellular lipases that encourage triglyceride hydrolysis
Session 1, 2019 – FDS202 Page 5 of 12
18. Nitrite, a food preservative, has over the years attracted some scrutiny because:
a. It is only very poorly inhibitory to bacteria
b. It reacts with amino acids to form nitrates
c. It reacts with air to form carcinogenic compounds
d. It reacts with secondary amines to produce N-nitrosamine, a carcinogen
e. It converts myoglobin in meat to oxyhaemoglobin
19. The change in pH of mammalian muscle after death is due to which of the following?
a. The metabolism of proteins to produce amino acids
b. The increased redox potential following cell metabolism
c. The liberation of fatty acids from intracellular storage sites
d. The glycolytic breakdown of glycogen and the accumulation of lactic acid
e. The glycolytic breakdown of glycogen and the accumulation of acetic acid
20. Apart from water, the major components of cow’s milk are which of the following?
a. Casein and fat
b. Casein, fat and lactose
c. polysaccharides and fat
d. Salt and lysozyme
e. Lactose, fructose and casein
21. The following is a correct combination of thermodurics that can survive mild pasteurisation in milk:
a. Pseudomonas, Acinetobacter, Alcaligenes, Flavobacterium, Bacillus
b. Microbacterium, Micrococcus, Enterococcus, Lactobacillus, Alcaligenes tolerans
c. Microbacterium, Micrococcus, Enterococcus, Lactobacillus, Escherichia coli
d. Pseudomonas, Acinetobacter, Alcaligenes, Flavobacterium, Bacillus, Microbacterium
e. A combination of b and d
22. The real incidence of food-borne disease compared to the reported incidence is estimated to be:
a. 1:1
b. 1:50
c. between 25:1 and 100:1
d. between 2:1 and 10:1
e. very close to 100%
Session 1, 2019 – FDS202 Page 6 of 12
23. After death, the pH of mammalian muscle drops to approximately:
a. 4.0 – 4.5
b. 5.4 – 5.6
c. 6.5 – 6.8
d. 7.2 – 7.5
e. 8.5 – 8.8
24. Ultraviolet radiation causes the death of micro-organisms mainly by:
a. The formation of covalently linked dimers between adjacent adenine bases in DNA
b. The formation of hydrogen bonds between H+ and OHˉ ions
c. The formation of covalently linked dimers between adjacent thymine bases in DNA
d. Absorption of the energy causing cells to heat up
e. The absorption of free energy by sulphur containing amino acids
25. Gamma radiation causes the death of micro-organisms by:
a. The formation of covalently linked dimers between adjacent purine bases in DNA
b. The formation of hydrogen bonds between H+ and OHˉ ions
c. The formation of covalently linked dimers between adjacent thymine bases in DNA
d. The production of free radicals that react with chromosomal DNA
e. The absorption of free energy by sulphur containing amino acids
26. A major disadvantage of the use of UV radiation in food processing is:
a. It can cause pigmentation of the food
b. It causes the food to release radiation after packaging
c. It has poor penetration into foods and liquids containing solutes
d. It causes uneven heating of the food
e. It kills viruses very efficiently but bacteria very poorly
27. In countries with high standards of food safety, the most common cause for microbial food borne diseases is which of the following?
a. high humidity
b. cross-contamination
c. poor sanitation
d. lack of wide-spread vaccination
e. temperature abuse
Session 1, 2019 – FDS202 Page 7 of 12
28. To confirm the identity of Staphylococcus aureus and to distinguish it from Staphylococcus epidermidis, a test is performed to detect which enzyme?
a. Amylase
b. Phosphatase
c. Catalase
d. Coagulase
e. Gluconase
29. The presumptive identification of Staphylococcus aureus is determined by the appearance of deep black bacterial colonies on what agar?
a. Violet Red Bile agar
b. Baird-Parker agar
c. Egg Yolk agar
d. Mannitol Salts agar
e. Rappaport-Vassiliadis agar
30. With regard to the use of gases to inhibit microbial growth in foods, the main difference between CAP and MAP is which of the following?
a. With CAP, the levels of gases are constantly monitored and adjusted
b. In MAP, the packaging is permeable to the surrounding atmosphere
c. CAP and MAP are essentially identical methods
d. In MAP the gas levels remain constant throughout storage
e. All of the above options are correct
31. Which medium is used for enrichment of Clostridium botulinum from a food sample?
a. Cooked meat broth
b. Lysine agar
c. Horse blood agar
d. Sabouraud’s agar
e. Serum agar
32. Botulism, caused by Clostridium botulinum is best described as:
a. a mild gastroenteritis that resolves in a few days
b. an often fatal, neurological disease
c. an infection of the body by live bacterial cells
d. a disease that causes strong contraction of muscles
e. none of the options are correct
Session 1, 2019 – FDS202 Page 8 of 12
33. Salmonella are best described by which of the following statements?
a. Gram positive bacteria that normally live in soil and water
b. Endospore forming bacteria, widely distributed in the environment
c. Common inhabitants of the gastrointestinal flora of animals
d. Gram negative rods
e. options (c) and (d) are both correct
34. A selective and differential medium used to isolate Escherichia coli is:
a. Baird-Parker agar
b. Blood agar
c. Tomato juice agar
d. Lysine agar
e. MacConkey agar
35. Listeria monocytogenes can cause invasive diseases that are most severe in:
a. pregnant women and the elderly
b. healthy young adults (18-25 yrs)
c. young women
d. meat handlers and veterinarians
e. none of the options is correct
36. The four major categories of diarrhoeagenic Escherichia coli can be distinguished based on their:
a. Lysogenic bacteriophages
b. Distinct, genetically encoded virulence factors
c. Association with endotoxins
d. Independence from capsule production
e. Lactose fermentation and similar biochemical reactions.
37. Select the most correct answer regarding bovine spongiform encephalopathy (BSE):
a. These are bacteria that can only grow inside human cells
b. These are prions, which are proteins that can cause disease
c. They are associated with the nervous tissue of diseased cattle
d. They are easily inactivated by heat or by chemical disinfectants
e. Options b. and c. are both correct
38. Bacteriocins are best described as:
a. peptides secreted by bacteria that inhibit other bacterial species
b. bacterial carbohydrates that inhibit a wide variety of other species
c. components of the Gram positive cell wall
d. bacterial genes that code for antibiotics like penicillin
e. fungal toxins (mycotoxins)
Session 1, 2019 – FDS202 Page 9 of 12
39. High pressure processing (HPP), also called Pascalization, can be best described as:
a. A method for rapid transfer of liquid foods between storage vats
b. A form of homogenisation used in milk processing
c. The application of very-high pressure to kill microbes
d. The simultaneous application of very-high pressure and high temperatures
e. A pasteurisation method performed at normal atmospheric pressure
40. In hazard analysis of food production processes, it is important to identify microbial hazards related to:
a. Microbial flora of raw materials or ingredients
b. Potential for microbial contamination at various steps in the processing
c. Microbial flora associated with packaging materials
d. Steps or conditions that allow microbial growth to occur
e. All of the above options are correct.
[Go to the next section, on the following page] Session 1, 2019 – FDS202 Page 10 of 12
SECTION 2 – SHORT ANSWER QUESTIONS –
Question 1. (10 marks total)
a) Name 2 genera of bacteria that dominate the normal flora of dry skin in humans. (2 marks)
b) Why is it that fruit spoilage is much more commonly associated with yeasts and moulds than with bacteria? (2 marks)
c) Describe three (3) ways that CO2 can inhibit microbial growth? (6 marks)
Question 2. (10 marks total)
a) Outline the inhibitory or damaging effects that occur to bacterial cells as they are cooled from room temperature to freezing at -18°C. [there are at least 3 such effects] (5 marks)
b) How does vacuum packing (VP) differ from modified atmosphere packing (MAP) in regard to the prevention of food spoilage by bacteria? (5 marks)
Question 3. (10 marks total)
In relation to food microbiology briefly define the following terms and abbreviations: (2 marks for each term)
a. Nisin
b. Chymosin
c. Lactose
d. EHEC
e. Real Time PCR
Question 4. (10 marks total)
Write a brief essay on techniques that are used for detection and enumeration of microorganisms in foods, using diagrams to illustrate your answer. (10 marks) Session 1, 2019 – FDS202 Page 11 of 12
Question 5. (10 marks total)
a) What is scombroid poisoning and how does it occur? (4 marks)
b) Describe the features of food borne illness caused by Campylobacter species, including the type of organism, source, transmission, prevention and type of disease(s). (6 marks)
Question 6. (10 marks total)
By the end of a 6-hour air flight, many of the passengers had already become violently ill, with vomiting and diarrhoea. Illness appeared within 1-2 hours after the meal had been served. Passengers were allowed a choice of 2 different dishes for this meal. A food poisoning incident is suspected. Answer the questions (a and b) below.
a) Given the relatively short time between the meal and first symptoms, what type of food poisoning do you think is most likely? Give the full names of two likely pathogenic bacteria (from different genera). (2 marks)
b) If you assume the outbreak was caused by the organism you have given in part (a), what laboratory evidence would provide the most convincing case that the symptoms were indeed caused by this organism? End your answer with a sentence that logically links the evidence to your final conclusion. (8 marks)
Question 7. (10 marks total)
a) Name three species of lactic acid producing bacteria used in dairy fermentations. (3 marks)
b) Define the terms homofermentative and heterofermentative. (2 marks)
Answer Part c) or d) but not both.
c) Discuss the importance of genetics in strain development of lactic acid bacteria. (5 marks)
OR
d) Describe how diacetyl overproducing strains of lactic acid bacteria are engineered. (5 marks)
Session 1, 2019 – FDS202 Page 12 of 12
Question 8. (10 marks total)
Compare and contrast HACCP planning and simple End Point Testing in food production. Describe a real life example of where testing failed and outline the possible consequences of such a failure. (10 marks)
