Final Exam

Question 1

How are food ecosystems impacted?

Answer 1

By generation and utilization of energy

Affect host ecosystems when ingested

Question 2

What are intrinsic food ecosystems?

Answer 2

Factors inherent to the food:
pH
Aw
Nutrients
Changes over time as bacteria grow and produce by-products

Question 3

What are extrinsic food ecosystems?

Answer 3

Factors external to the food:
Temp
Gases in atmosphere
Change over time as bacteria grow and produce by-products

Question 4

What are the stages of bacterial growth & division?

Answer 4

Lag phase (no growth; min number)
Log/exponential growth phase
Stationary phase (no growth; max number)
Deat/logarithmic decline phase

Question 5

What are the requirements for bacterial growth and division?

Answer 5

Carbon (anabolism)
Energy (catabolism)
Source of electrons
Electron acceptor

Question 6

What are the types of carbon for bacterial building?

Answer 6

Autotrophic: carbon from CO2 carbon fixation
Heterotropic: carbon from organic compounds
Mixotrophic: both auto & heterotrophy

Question 7

What are the types of energy sources of bacteria?

Answer 7

Chemotrophic: energy from external chemical compounds
Phototrophic: energy from light

Question 8

What are the types of sources of electrons for bacteria?

Answer 8

Lithotrophic: reducing equivalents from inorganic compounds
Organotrophic: reducing equivalents from organic compounds

Question 9

What are the types of electron acceptors?

Answer 9

Aerobic organisms: use oxygen
Fermentation: use organic carbon (fermentative organisms = anaerobes)
- Succinate fermentation or oxalate fermentation: low energy-yielding fermentation forms
Facultative anaerobes: grow with or without oxygen
Strict anaerobes:
- Denitrification: nitrate
- Sulfate reduction: sulfate
- Acetogenesis: CO2

Question 10

Lactic acid bacteria:

Answer 10

Produce relatively large quantities of lactic acid from carbohydrates

Question 11

Proteolytic bacteria:

Answer 11

Hydrolyze proteins in food to produce extracellular proteinases

Question 12

Lipolytic bacteria:

Answer 12

Hydrolyze triglycerides to produce extracellular lipases

Question 13

Types of bacteria based on temperature:

Answer 13

Thermophilic: can grow above 50C
Thermoduric: can survive pasteurization temps
Psychotropic: can grow at fridge temp
Cryophilic: can grow at freezer temp

Question 14

Halophilic bacteria:

Answer 14

survive high salt (above 10%) concentrations

Question 15

Aciduric bacteria:

Answer 15

Survive low pH

Question 16

Osmophilic bacteria:

Answer 16

Grow at higher osmotic environments

Question 17

What is the difference between coliforms and fecal coliforms?

Answer 17

Both: used as an index for sanitation

Fecal coliforms: presence indicates fecal contamination

Question 18

What are enteric pathogens?

Answer 18

Can cause gastrointestinal infection

Question 19

What is the number of bacteria in meat?

Answer 19

Right after slaughter: 10^1-3cells/inch
Ground meat: 10^4-5cells/gram
Heat processed: 10^1-2cells/gram

Question 20

What is the main bacterial issue to meat?

Answer 20

Psychotrophic bacteria (ex. Listeria)
Due to meat being chilled during storage
Many heat processed meats to reduce bacteria & increase shelf life (over 50 days)
- Can be stored anaerobically

Question 21

What is the number of bacteria in raw milk?

Answer 21

Raw milk: 10^3 cells/mL
- Higher in cows with mastitis
Pastuerizaed milk: 10^4cells/mL

Question 22

What causes milk to be good for microbial growth?

Answer 22

High in carbs (lactose) & protein

- Carbon and energy sources

Question 23

What best bacteria grow in milk?

Answer 23

Before pasteurization = psychotrophs

After pasteurization = thermodurics & bacteria that enter post pasteurzation (from equipment, handling, air…)

Question 24

Why are fish and shellfish good or bad for bacterial growth?

Answer 24

Good:
- High in protein 
- High Aw, pH
- Availalbe carbon and nitrogen
Bad:
- Low in fat & carbs
- HIgh in salt (need halophiles)

Question 25

What makes vegetables, fruits, and nuts good/bad for bacterial growth?

Answer 25

``` High in carbs Stored at room temp pH: - Veggies = 5-7 - Fruits = 4.5 or lower ```

Question 26

How much bacteria is in vegetables and fruit?

Answer 26

``` Veggies = 10^4-7 cells/gram Fruits = 10^3-4 cells/gram ```

Question 27

Why is pH important in canned foods?

Answer 27

If below 4.6 = mesophiles germinate & produce toxins | If above 4.6 = mesophiles not an issue unless temperature abused

Question 28

What major pathogen is in canned foods?

Answer 28

Staphylococcus | The toxins can survive canning process

Question 29

What is the cell membrane responsible for?

Answer 29

Solute transport Electron transport Establishment of electrochemical gradients ATP synthesis Synthesis of lipids Secretion of proteins Secretion & uptake of intercellular signals

Question 30

Why does turgor pressure exist on bacteria?

Answer 30

Bacteria live in environments that are more dilute than the cytoplasm Causes net influx of water, resulting in pressure being directed out against the cell wall

Question 31

What is the difference between gram-negative & gram-positive bacteria?

Answer 31

``` Gram + - Peptidoglycan cell wall (w/ Lipoteichoic acid comprising 30-60% of weight) - Plasma membrane - Fimbrae & pili in very few Gram - - Outer lipid membrane (w/ lipopolysaccharide consisting lipid A, core, & O antigen) - Peptidoglycan - Plasma membrane - Fimbrae & pili in most ```

Question 32

What is the process of the gram stain?

Answer 32

1. Apply crystal violet (purple) 2. Apply iodine (to bind crystal violet to gram +) - Traps crystal violet in peptidoglycan of gram + (called mordant) 3. Wash in alcohol to remove from gram - 4. Add safranin (counterstain pink) - Binds to gram - to see under light microscope

Question 33

Function of fimbrae & pili:

Answer 33

Mediate attachment to cells Mediate genetic exchance Transmit DNA

Question 34

Types of pili:

Answer 34

Adhesive pili: have adhesins Sex pili: attach to each other & transmit DNA from a donor cell - Found in enteric bacteria (not universal) - Ex. F plasmid contains code for sex pili in E. coli

Question 35

What are the serotypes based on cell surface structures?

Answer 35

``` K antigen (capsule) O antigen (lipopolysaccharide) F antigen (fimbriae) H antigen (flagella) * typing scheme differs between each type of bacteria ```

Question 36

What are injured cells?

Answer 36

Due to sublethal stressors Unable to grow on selective media, but can grow on non-selective media - More sensitive to selective agents & may have increased nutritional requirements

Question 37

Why are injured cells important in food microbiology?

Answer 37

- If they appear dead, resistance will be underestimated & the "kill" values will be low - May escape detection post-processing, leading to faster spoilage - "selective agent" can be a common food ingredient such as sald, organic acid, or suboptimal temperatures

Question 38

How are injured cells repaired?

Answer 38

Required new RNA & protein synthesis May seem an extended lag phase Reestablishes membrane integrity Temperature is critical (can be delayed w/ suboptimal temp) Peroxide detox agent can help damage from oxygen toxicity

Question 39

What is VBNC?

Answer 39

Viable but not culturable - Can't be cultured on any media Survival strategy for non-sporulating species - Ex. Salmonella, Campylobacter, Excherichia, Shigella, Vibrio Morphologically different from a normal vegetative cell Caused mostly by nutrient limitation; also by salt concentration, chemicals, or temp shifts - Removed by temp shifts and gradual return of nutrients Up to 99% of bacteria can be unculturable

Question 40

How can VBNC cells be demonstrated?

Answer 40

Cytological methods | Substrate responsive metabolism

Question 41

How is VBNC demonstrated through cytological methods?

Answer 41

Structural integrity indicates life, deteriation indicates cell death Fluorescent nucleic acid stains (red) are added - If permeate cell, deterioration occurred & cell is dead Color stain used for cell wall (green) - If cell wall is intact will see green; if deteriorated will see red

Question 42

How is VBNC demonstrated through substrate responsive metabolism?

Answer 42

Incubated with a ntureint and an antibiotic - Inhibits cell division Live cells elongate but do not divide * used for Lm