Lecture 4: Spoilage/Pathogens

Question 1

How do yeasts reproduce?

Answer 1

1. Budding

2. Fission

Question 2

Name and describe the two different possible life stages of bacteria

Answer 2

1. Vegetative cells (Normal organism)
   • Vegetative pathogen - active, growing form; Easier to kill
   • Growing or able to grow
2. Spores - When conditions are poor; harder to kill
   •Not able to grow - lays dormant until conditions are ripe (100s of years)
   •Resistant to heat, cold, drying (survive pasteurization)
   • Will germinate and grow under ideal conditions
   • eg: C. botulinum, Bacillus

Question 3

Name and describe the growth factors of pathogens

Answer 3

1. Food
 • Water
• Source of energy (food) - CHO, PRO; Less common starches & cellulose
 • Source of nitrogen (amino acids)
 • Vitamins and related growth factors
• Minerals
2. Acidity - Majority of foods are <7pH
 •Bacteria - grow in 7-9pH range
•Molds cover widest range - 2-12pH
 • Yeast is middle
3. Time  
 • 2hr Danger Zone (40-140 F)
 •Spoilage organisms may grow slowly over the shelf life of food (months to years)
4. Temp 
 • Majority organisms are mesophiles (50-122 F)
 •But are organisms that can grow from 14-194 F
5. Oxygen
6. Moisture/ Water Activity
 •Influenced by the presence of solutes (salt, sugar)
 •Does not correlate with moisture
 •>.85 Aw

Question 4

What is the relationship between spoilage and foodborne illness?

Answer 4

Spoilage - Microorganisms cause an undesired change to the food’s smell, taste, appearance, texture; No human health risk
• Yeast in juice
• Mold on cheese & bread
•Bacteria - spoiled milk, sulphur-y smell, swollen packaging

Foodborne Illness/ Pathogenic - Microorganism causes illness
• Public health hazards

Question 5

Describe Clostridium botulinium

Answer 5

• Anaerobic
• Spore forming
• Produce toxin- botulin (same toxin as Botox)
• Most common foods:
- home-canned goods
- low acid foods (i.e. asparagus, beets, corn)
- Honey (infant)
• Has to process in 121oC to kill both spores and bacteria cells.

Question 6

Describe Escherichia coli

Answer 6

• Facultative anaerobic
• Non-spore forming
• Produce toxin - shiga
food vehicles: meat, fresh produce
- exist in all warm blood animals’ intestine, feces and raw meat contamination
• Bacteria cells is easy to kill (71oC but spores are heat resistant 100oC)

Question 7

Describe Listeria monocytogenes

Answer 7

• Facultative anaerobic
• Non-spore forming
• Pregnant women need to watch out for it.

Question 8

Describe Salmonella

Answer 8

• Facultative anaerobic
• Non-spore forming
• All strains are pathogenic
• Poultry and eggs are most important carrier
• Killed by heat treatment (72oC).

Question 9

If a food contains 24,000 CFU/mL, how many serial dilutions you have to make in order to get ideal plate count.

Answer 9

Goal is to get 30-300 CFU/ml in order to accurately count bacteria. Dilutions are by factors of 10, so that means you want to get the 24,000 per sample down to 240 (to fit within the 30-300 parameters). So in order to do that, you move the decimal (or divide by 10) two times. Therefore, you need to do two dilutions of factors of 10