Lecture 11: Food Microbiology

Question 1

1) Give examples of microbes in food
2) What helps produce cheese?

Answer 1

1) Molds help us make soy sauce, beer and wine fermentation, bacteria make air pockets and holes in swiss cheese
2) Bacterial lactic acid production

Question 2

1) Why does food go bad?
2) What are the two types of factors of microbial growth in foods?

Answer 2

1) Food goes bad because of microbes; for example, milk curdles (proteins coagulate) while going bad and pH decreases. This allows molds and yeast to take over.
2) Intrinsic and extrinsic

Question 3

1) List the intrinsic factors of microbial growth in foods
2) List the extrinsic factors of microbial growth in foods

Answer 3

1) Intrinsic: Composition, physical, and biological state
2) Extrinsic: Temperature, relative humidity, gasses, contaminating microorganisms

Question 4

1) How does temperature and heat affect microbial growth? How can atmosphere be changed to affect growth?
2) Give 2 examples of foods with antimicrobial activity

Answer 4

1) Low temperature and low humidity decrease growth. CO2 can be injected into packaging to prevent growth during shipment.
2) Fruits and vegetables have coumarins (antimicrobial) and spices are antimicrobial

Question 5

Describe the 3 Genome Watch articles discussed in class

Answer 5

1) -omics: for example, metabolomics, lipidomics (study metabolism pathways), proteomics (study proteins) was used to study lactobacillus (beneficial bacteria) in bee guts
2) CRISPR-CAS
3) Those with COVID-19 had a limited amount of immunomodulatory bacteria; made their symptoms more severe

Question 6

Describe the 6 Research Highlights articles discussed in class

Answer 6

1) Gut flora impact on obesity in IBD
2) Phage in the Pseudomonas strain can make proteins that protect phage DNA and form crystalline droplets that coat the host cell
3) Increased CO2 emission of soil bacteria grown in “global warming” conditions (vs control)
4) Necro signaling: Dying bacteria can secrete signals to living cells to warn about antibiotics
5) Virus causes host to attract mosquitos; but can be reversed
6) COVID-19 loss of smell; does not infect olfactory cells but changes their surface

Question 7

What are some examples of specific intrinsic factors for microbial growth on food?

Answer 7

1) Food composition
2) pH
3) Physical structure
4) Availability of water

Question 8

1) Low pH of food leads to what kind of microbial growth? 2) What about high pH?

Answer 8

1) Low leads to yeasts and molds
2) High leads to bacteria

Question 9

How is the physical structure of food altered when we eat?

Answer 9

Grinding, mixing, etc increases surface area

Question 10

What protection against microbial growth do fruits and vegetables have?

Answer 10

Spillage microorganisms have enzymes that protect

Question 11

How does water affect food spoilage? What else can affect food spoilage?

Answer 11

There is less spoilage if 1) dry or 2) add sugar or salt

Question 12

Give 9 examples of methods used to control food spoilage

Answer 12

1) Filtration
2) Low-temperature
3) High-temperature
4) Water availability
5) Ultra-high temp pasteurization
6) Chemical-based preservation
7) Radiation
8) Microbial product-based inhibition
9) Packaging

Question 13

Define filtration and low-temperature

Answer 13

Filtration: removes microbes from liquids
Low temperature: slows but doesn’t kill

Question 14

1) Give 2 examples of high temperature controlling microbes on food
2) How can water availability control microbes on food?

Answer 14

1) High temperature: pasteurization, canning
2) Water availability: drying vs storing in liquid

Question 15

________ microorganisms prefer a dry environment
________ microbes grow best under osmotic conditions

Answer 15

-xerophilic; -osmophilic

Question 16

1) Is ultra high temperature pasteurization shelf-stable? What does it kill?
2) What is chemical-based preservation closely regulated by?

Answer 16

1) Shelf-stable, kills bacteria
2) The FDA

Question 17

1) When is radiation effective at controlling microbes? What does it use?
2) Give 2 examples of microbial product-based inhibition

Answer 17

Radiation: effective for moist foods (radappertization); also use electron beams
Microbial product-based inhibition: bacteriocins (nisin) and bacteriophage spray

Question 18

Describe how packaging can control microorganisms on food

Answer 18

Through a ‘modified atmosphere’ (60% CO2 or high-O2)

Question 19

1) Are molds unicellular or multicellular?
2) What can molds make?
3) What can molds cause?
4) How do molds reproduce?
5) What do molds secrete?

Answer 19

1) Can adopt multicellular arrangement
2) Can make filaments (fuzzy)
3) Cause allergies
4) Reproduce through spores
5) Secrete enzymes
Yeast: single-celled, can cause infection if immunocompromised, reproduce through mitosis (budding), fermentation of sugars into CO2 plus alcohol.

Question 20

1) Are yeast single-celled or multicellular?
2) What can yeast cause? When?
3) How do yeast reproduce?
4) What do yeast do to sugar?

Answer 20

1) Single-celled
2) Can cause infection if immunocompromised
3) Reproduce through mitosis (budding)
4) Fermentation of sugars into CO2 and alcohol.

Question 21

What are the two types of food related disease? Describe them.

Answer 21

1) Food-borne infections: ingestion of pathogen-grown-invasion/ toxin production (food poisoning) (toxins made in body)
2) Food intoxications: results from microbial growth in food products (toxins made in food)

Question 22

Name 6 food-borne microbes

Answer 22

1) Salmonella
2) Norovirus
3) Campylobacter
4) Toxoplasma
5) E. coli 0157
6) Listeria

Question 23

What is the incubation period, symptoms, and food sources of Salmonella?

Answer 23

Incubation: 8-48 hours
Symptoms: Gastroenteritis (diarrhea, fever, vomiting).
Food source: Fruits, vegetables, poultry, eggs, cheese

Question 24

What is the incubation period, symptoms, and food sources of Norovirus?

Answer 24

Incubation: 12-48 hours (‘cruise ship virus’)
Symptoms: Diarrhea, fever, nausea
Food source: Produce, shellfish, salad, sandwiches

Question 25

What is the incubation period, symptoms, and food sources of Campylobacter?

Answer 25

Incubation: 2-5 days
Symptoms: Diarrhea, fever, cramps
Food source: Poultry, contaminated water

Question 26

What is the incubation period, symptoms, and food sources of Toxoplasma?

Answer 26

Incubation: 1-3 weeks
Enlarged lymph nodes, headaches, myalgia.
Food source: Raw meat, contaminated water (& cat litter box)

Question 27

What is the incubation period, symptoms, and food sources of E. coli 0157?

Answer 27

Incubation: 1-10 days
Symptoms: Severe diarrhea, vomiting, HUS (hemolytic uric syndrome)
Food source: Contaminated water, raw milk/ fruit/ veggies, hamburger meat

Question 28

What is the incubation period, symptoms, and food sources of Listeria?

Answer 28

Incubation: 3-70 days
Symptoms: Fever, stiff neck, confusion, myalgia
Food source: Deli meats, hot dogs, raw milk and dairy, soft cheese (survives in fridge).

Question 29

1) Does food intoxication require growth of disease-causing microbes?
2) How fast do symptoms manifest?

Answer 29

1) Growth of disease-causing microorganisms not required
2) Symptoms manifest quickly

Question 30

1) Where is Staphylococcus aureus (SA) normally found?
2) Describe when its growth and toxin production occurs and if it’s heat-stable
3) What are its symptoms and how fast do they manifest?

Answer 30

1) Introduced into food during preparation
2) Growth and toxin (heat-stable) production occurs as food sits out.
3) Nausea, vomiting, stomach cramps, and diarrhea as little as 30 minutes after you eat something (up to 2 hours).

Question 31

1) Where is Clostridium perfringens found?
2) What does it do in its production of gut-toxin?

Answer 31

1) Growth in rewarmed meat dishes
2) Sporulation in gut-toxin production

Question 32

1) Where is Botulinum found?
2) Describe its mortality

Answer 32

1) Growth in anoxic foods (canned goods) = toxin.
2) Toxin absorbed in gut = high mortality.

Question 33

What are the two forms of Bacillus cereus?

Answer 33

Short form (emetic form) and long form (diarrheal form)

Question 34

Name the 2 forms of Bacillus cereus and describe their heat stability, incubation times, and symptoms

Answer 34

1) Emetic form: Toxin heat-stable, 1-6 hours, vomiting, and cramps
-Fried rice, sprouts, cucumbers
2) Diarrheal form: Toxins heat-labile, 8-16 hours, diarrhea and cramps

Question 35

What are the 4 places in which food can be contaminated?

Answer 35

1) Production: spraying fields with contaminated water, contamination before harvest
2) Processing: using contaminated water to wash
3) Distribution: being left in warm weather before distribution
4) Preparation: being contaminated by a human in the kitchen

Question 36

What are 3 traits found in the ideal food-borne pathogen detection method?

Answer 36

1) Specificity and sensitivity
2) Speed
3) Simplicity.

Question 37

Describe the 3 levels of food-borne pathogen testing and when each happens

Answer 37

1st level: Testing to prevent (before it leaves farm)
2nd level: Testing to protect (prior to consumption)
3rd level: Testing to recover (determine origin of an outbreak)

Question 38

True or false: It can take a lot of time to detect pathogens

Answer 38

True

Question 39

Microbes are involved in what 3 aspects of food?

Answer 39

Safety, quality, and nutrition

Question 40

Name 4 types of groups that may respond to a food-borne pathogen outbreak

Answer 40

1) Local agencies
2) State agencies
3) CDC
4) Federal regulatory agencies: FDA, USDA’s Food Safety and Inspection Service (FSIS), etc

Question 41

How can lactic acid bacteria (LAB) be used? (5 ways).
Describe each.

Answer 41

1) Mesophilic fermentation: Lactococcus lactis used to make milk richer; buttery flavor.
2) Thermophilic fermentation: S. thermophilus and L. bulgaricus
3) Probiotic: live microorganisms, which when administered in adequate amounts, confer a health benefit for the host
4) Microbial dietary adjuvants: immunomodulation, control of diarrhea, anticancer, Crohn’s disease
5) Ethanolic fermentation: wine, beer, etc

Question 42

What temperatures do mesophilic and thermophilic lactic acid fermentation take place at?

Answer 42

1) Mesophilic: 20-30C
2) Thermophilic: 45C