Final Exam Flashcards
How are food ecosystems impacted?
By generation and utilization of energy
Affect host ecosystems when ingested
What are intrinsic food ecosystems?
Factors inherent to the food: pH Aw Nutrients Changes over time as bacteria grow and produce by-products
What are extrinsic food ecosystems?
Factors external to the food:
Temp
Gases in atmosphere
Change over time as bacteria grow and produce by-products
What are the stages of bacterial growth & division?
Lag phase (no growth; min number)
Log/exponential growth phase
Stationary phase (no growth; max number)
Deat/logarithmic decline phase
What are the requirements for bacterial growth and division?
Carbon (anabolism)
Energy (catabolism)
Source of electrons
Electron acceptor
What are the types of carbon for bacterial building?
Autotrophic: carbon from CO2 carbon fixation
Heterotropic: carbon from organic compounds
Mixotrophic: both auto & heterotrophy
What are the types of energy sources of bacteria?
Chemotrophic: energy from external chemical compounds
Phototrophic: energy from light
What are the types of sources of electrons for bacteria?
Lithotrophic: reducing equivalents from inorganic compounds
Organotrophic: reducing equivalents from organic compounds
What are the types of electron acceptors?
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
Lactic acid bacteria:
Produce relatively large quantities of lactic acid from carbohydrates
Proteolytic bacteria:
Hydrolyze proteins in food to produce extracellular proteinases
Lipolytic bacteria:
Hydrolyze triglycerides to produce extracellular lipases
Types of bacteria based on temperature:
Thermophilic: can grow above 50C
Thermoduric: can survive pasteurization temps
Psychotropic: can grow at fridge temp
Cryophilic: can grow at freezer temp
Halophilic bacteria:
survive high salt (above 10%) concentrations
Aciduric bacteria:
Survive low pH
Osmophilic bacteria:
Grow at higher osmotic environments
What is the difference between coliforms and fecal coliforms?
Both: used as an index for sanitation
Fecal coliforms: presence indicates fecal contamination
What are enteric pathogens?
Can cause gastrointestinal infection
What is the number of bacteria in meat?
Right after slaughter: 10^1-3cells/inch
Ground meat: 10^4-5cells/gram
Heat processed: 10^1-2cells/gram
What is the main bacterial issue to meat?
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
What is the number of bacteria in raw milk?
Raw milk: 10^3 cells/mL
- Higher in cows with mastitis
Pastuerizaed milk: 10^4cells/mL
What causes milk to be good for microbial growth?
High in carbs (lactose) & protein
- Carbon and energy sources
What best bacteria grow in milk?
Before pasteurization = psychotrophs
After pasteurization = thermodurics & bacteria that enter post pasteurzation (from equipment, handling, air…)
Why are fish and shellfish good or bad for bacterial growth?
Good: - High in protein - High Aw, pH - Availalbe carbon and nitrogen Bad: - Low in fat & carbs - HIgh in salt (need halophiles)
What makes vegetables, fruits, and nuts good/bad for bacterial growth?
High in carbs Stored at room temp pH: - Veggies = 5-7 - Fruits = 4.5 or lower
How much bacteria is in vegetables and fruit?
Veggies = 10^4-7 cells/gram Fruits = 10^3-4 cells/gram
Why is pH important in canned foods?
If below 4.6 = mesophiles germinate & produce toxins
If above 4.6 = mesophiles not an issue unless temperature abused
What major pathogen is in canned foods?
Staphylococcus
The toxins can survive canning process
What is the cell membrane responsible for?
Solute transport
Electron transport
Establishment of electrochemical gradients
ATP synthesis
Synthesis of lipids
Secretion of proteins
Secretion & uptake of intercellular signals
Why does turgor pressure exist on bacteria?
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
What is the difference between gram-negative & gram-positive bacteria?
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
What is the process of the gram stain?
- Apply crystal violet (purple)
- Apply iodine (to bind crystal violet to gram +)
- Traps crystal violet in peptidoglycan of gram + (called mordant) - Wash in alcohol to remove from gram -
- Add safranin (counterstain pink)
- Binds to gram - to see under light microscope
Function of fimbrae & pili:
Mediate attachment to cells
Mediate genetic exchance
Transmit DNA
Types of pili:
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
What are the serotypes based on cell surface structures?
K antigen (capsule) O antigen (lipopolysaccharide) F antigen (fimbriae) H antigen (flagella) * typing scheme differs between each type of bacteria
What are injured cells?
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
Why are injured cells important in food microbiology?
- 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
How are injured cells repaired?
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
What is VBNC?
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
How can VBNC cells be demonstrated?
Cytological methods
Substrate responsive metabolism
How is VBNC demonstrated through cytological methods?
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
How is VBNC demonstrated through substrate responsive metabolism?
Incubated with a ntureint and an antibiotic
- Inhibits cell division
Live cells elongate but do not divide
* used for Lm
