Midterm I Flashcards
What is an ecosystem?
Series of interactions between the environment & organisms that inhabit it
Impacted by generation & utilization of energy
Food ecosystems affect host ecosystems
What are the two types of food ecosystems compositions?
Intrinsic: factors inherent to the food - pH - Water activity - Nutrients Extrinsic: factors external to the food - Temperature - Gaseous atmosphere Can change over time as bacteria grow & produce bi-products Can be heterogenous on a micrometer scale
What are the 4 stages of bacterial growth & division?
- Lag phase
- log/exponential growth phase
- Stationary phase
- Death/ log decline phase
What is needed for bacterial growth & division?
Bacteria must have carbon (Anabolism)
- To build the array of chemical substances they are composed of
Bacteria must have a source of energy (catabolism)
Bacteria must have a source of electrons
- To use in energy conservation & biosynthetic reactions
Bacteria must have an electron acceptor
What are the ways bacteria gain carbon?
Autotrophic: carbon from Co2 through carbon fixation
Heterotrophic: carbon from organic compounds
Mixotrophic: autotrophic + heterotrophic
What are the sources of energy for bacteria?
Chemotrophic: energy is obtained from external chemical compounds
Phototrophic: energy is obtained from light
What are the sources of electrons?
LIthotrophic: reducing equivalents come from inorganic compounds
Organotrophic: reducing equivalents come from organic compounds
What are the different electron acceptors?
Aerobic organisms: use oxygen
Fermentation: use organic carbon (anaerobes)
- Other forms of fermentation = succinate fermentation or oxalate fermentation
- The other forms have very low energy yield
- Other anaerobic TEAs not common in food
Facultative anaerobes: can use oxygen or not
What are the non-taxonomic groupings of bacteria?
Lactic acid bacteria Proteolytic bacteria Lipolytic bacteria Thermophilic bacteria Thermoduric bacteria Psychrotrophic bacteria Cryophilic bacteria Halophilic bacteria Aciduring bacteria Osmophilic bacteria Spore formers Coliforms Fecal coliforms Enteric pathogens
If bacterial growth can occur, what will be the highest number of microbes?
Those that can grow optimally in the conditions provided (intrinsic & extrinsic)
Raw meat:
Carcasses after slaughter have 10^1-3cells/square inch (not many)
Meat is stored chilled
- Psychotropic organisms are main issue (Listeria)
Ground meat:
Can have 10^4-5cells/g
Lunch meat is heat processed & contains several chemicals to reduce bacteria & increase shelf life (50+ days)
- Heat processing can reduce microbes to 10^1-2cells/g
Stored anaerobically
- Psychotropic facultative anaerobes are main issue
Raw milk:
Contains 10^3cells/mL
- Higher in cows with mastitis
High in carbohydrates (lactose) & protein
- Great sources of carbon & energy for microbial growth
Refrigerated to preserve
- Psychotrophs still grow
Pasteurized milk:
Pasteurization kills all pathogens & most microbes, but milk quickly becomes contaminated from equipment, handling, & air
- Contains 10^4cells/mL
- Thermodurics survive pasteurization
Psychotrophs cause spoilage if milk is properly stored
Fish & shellfish:
Rich in protein & low in fat & carbs Microbes come from harvest environment - Based on water pollution & temperature - Can grow rapidly from Aw, pH, C & N availability Marine environment (high salt): - Halophiles are common Human waste polluted waters: - Several varied pathogens (including Vibrio cholerae)
Vegetables, fruit, & nuts:
High in carbs pH - Vegetables = 5.0-7.0 - Fruits = 4.5- Stored at room temp Consumed after minimal processing This all equals good growth for bacteria, yeasts, & mold Sources of contamination - Soil, water, air, animals, insects, birds, equipment, harvesters... Cell count: - Vegetables = 10^4-7cell/g - Fruits = 10^3-4cells/g
Canned food:
Hermetically sealed containers given heat treatment
pH:
- If below 4.6, mesophiles can germinate (produce toxins such as Clostridium)
- If above 4.6, mesophiles can’t grow but if cans are temperature abused, thermophilic spores grow & spoil food
Staphylococcus: can’t grow, but toxins can survive canning process
- If S. grows before canning, toxins survive & cause poisoning from consumption
What is the difference between coliforms and fecal coliforms?
Both: used as an index for sanitation
Fecal coliforms: also indicates presence of fecal contamination
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
What is the cell wall (peptidoglycan) responsible for?
Turgor pressure (protects for cell bursting)
- Bacteria live in environments more dilute than the cytoplasm (causes net influx of water)
Defining feature of gram + vs -
What does the cell wall of gram + bacteria contain?
Peptidoglycan cell wall
- With teichoic acids that comprises 30-60% of dry cell weight (several functions)
- With fimbrae & pili found on some bacteria
Plasma membrane
What does the gram - cell wall of bacteria contain?
Outer lipid membrane (lipopolysaccharide)
- Consists of lipid A, core, & repeating oligosaccharide (O-antigen)
With fimbrae & pili found on most bacteria
Peptidoglycan cell wall
Plasma membrane
How does the gram stain work?
Apply crystal violet (purple dye) Apply iodine (mordant) (traps crystal violet in peptidoglycan) Alcohol wash (decolorization of gram neg) Apply safranin (counterstain) (for gram neg) *Differentiates cell wall by physical properties (thickness/amt of peptidoglycan)
What is a bacterial capsule made of?
Polysaccharide
Multiple roles