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
What are fimbrae & pili?
Protein fibrils extending from the cell surface
Found in most gram -
Found in some gram +
Function not always known
- Mediate attachment to other cells or surfaces
- Adhesive pili have adhesins (proteins)
- Some mediate genetic exchange
- Sex pili used for bacteria to attach to each other & transmit DNA
Where are sex pili found?
Different from other pili
Found in enteric bacteria
Ex. E. coli: coded by a conjugative transmissible plasmid (F plasmid)
What are bacterial flagella?
Not the same as eukaryotic flagellum in composition, structure, & mechanisms of action
Stiff, helical filament
Rotates like a propeller
What are serotypes?
Groups within a single species of microorganisms that share distinctive surface structures
What are the different physiological & physical states of food bacteria?
Vegetative Injured Viable but not culturable Communicating in structured communities Sporulated
What are injured bacterial cells?
Caused by sublethal stressors
Unable to grow on selective media
- Can be more sensitive to selective agents
- Can have increased nutritional requirements
Repair: process by which cells recover from injury
Why are injured bacteria important?
If injured cells appear dead, the thermal resistance will be underestimated & the true “kill” values will be low
Injured cells escape routine detection post-processing which leads to faster spoilage or a safety problem
The “selective agent” may be common food ingredient
How do bacterial cells repair from injury?
Requires de novo RNA & protein synthesis May seem an extended lag phase Membrane integrity is reestablished Adding a peroxide detox agent can repair damage from oxygen toxicity Temperature is critical
What are viable but not culturable (VBNC) bacteria?
A state in which cells can’t be cultured even if viable
Survival strategy for non-sporulating species
Morphologically different from a normal vegetative cell
- Rod-shaped cells shrink & become spherical
Most often induced by nutrient limitation
- Also by salt conc., exposure to chemicals, temp shifts
Can be repaired by temp shifts & gradual return of nutrients
Up to 99% of bacteria may be unculturable
How can viability of VBNC bacteria be tested?
Cytological methods
Substrate responsive metabolism
What are the cytological methods of VBNC testing?
Structural integrity of cytoplasmic membrane indicates life
- Fluorescent NA stains (red) are incubated cells
- Counterstain (green) stains cell wall
- If bacteria stains green, cell wall is intact; if bacteria stains red, the membrane is damaged
What are the substrate responsive metabolism methods of VBNC testing?
Cells can be incubated in a nutrient & an antibiotic that inhibits cell division
- LIve cells will elongate, but no divide
Specific method for Lm
What is Quorum Sensing?
Regualtes genes that would be useless to isolated cells but useful to large populations
Low pop = extracellular conc. of signal molecule is low & signal molecule diffuses away from cell
High pop = Extracellular conc increases & all signal molecules diffuse back into cells causing:
- phenotypic response
In gram neg bacteria: N-acyl homoserine lactones (AHLs) act as the signaling molecule
Waht are the two cellular communication types?
Signal transduction: two component regulatory systems where one protein spans the membrane, picks up a signal, & reacts based on a response regulator protein
Quorum sensing: systems built on autoinducers which diffuse through the cellular membrane to initiate a specific response when a certain pop density has been reached
Difference: quorum sensing trigger molecule diffuses into the cell but not in signal transduction
What is signal transduction?
A way to communicate between bacteria
Consist of a histidine kinase receptor & a response regulator
Signal molecule binds to N-terminus on outside of membrane spanning kinase
- Protein kinase transduces signal across membrane using conformation change that increases kinetic activity on the inside
- Phosphorylates a response regulator protein that changes:
- gene expression
- enzymatic activity
- flagellar rotation
- another phenotype
What does Pleiotrophic mean?
Occurs when one gene influences two or more seemingly unrelated phenotypic traits
What is a biofilm?
An aggregation of cells (can be multiple species) into a heterogeneous complex structure that attaches to a solid surface
Composed by microcolonies hta have defined boundaries allowing fluid channels to run through the biomatrix
uses cell-to-cell communication (most likely Quorum sensing) so undifferentiated cells don’t fill the channels (don’t clog the pores)
- Channels needed to bring in nutrients & carry out waste
More resistant to heat, chemicals, sanitizers
Waht are endospores?
Differentiated cells that are very resistant to heat & can’t be easily destroyed (even by chemicals)
Found in most soil samples
What are the genetics of bacteria?
Most ahve one chromosome (main genomic element) that contain most of the genes
Usually circular chromosomes
Plastic (combinations of genes present different in each individual)
What are the different types of genomes?
Core genome: genes shared by all members of a certain group (species)
Pangenome: genes present in any member of a certain group
Accessory genome: genes present in a subset of members of a certain group
What are the mobile genetic elements of bacteria?
Bacteriophage
Plasmids
Pathogenicity Islands
Transposons
What is lysogenic conversion?
A prophage changing a non-pathogenic bacteria to a pathogen
What are defective prophages?
Bacteriophage that can’t form infective phage due to loss of essential genes
DNA elements of bacteria strains are suspected to be defective prophages
What is a plasmid?
Circular molecules of dsDNA which are self replicating
- Carry genes which encode for products that can benefit the bacteria under certain circumstances (but aren’t essential)
Can be few thousand to few hundred-thousands bp
Each cell can have multiple plasmids
Passed horizontally & vertically
What are pathogenicity islands?
Large DNA elements integrated into bacterial chromosomes containing genes for special properties on the bacteria that carry them
- Bacteria carrying them can occupy special ecological niches
Not carried by all strains & not integrated plasmids or prophages
Can move between bacteria
Have an integrase gene allowing them to integrate into a region of the host DNA
Have a repeated sequence at the ends of their sequences, involved in integration
What are transposons?
DNA elements able to hop between places in chromosomal DNA
Encodes its own transposaes, so it carries the ability to hop
Types:
- Insertion Sequence (IS) elements: single transposon
- Composite transposons: multiple acting as vehicle
What are insertion sequence (IS) elements?
Smallest transposons, only encoding the transposase
Can interrupt gene function by inserting in middle of gene
Usually have inverted repeat at either end
What are composite transposons?
When two IS elements bracket other genes & carry those genes with them when they move
What are the categories of foodborne diseases?
Intoxication
Infection
Toxicoinfection
What is intoxication?
Occurs after ingestion of a bacterial or mould toxin
Toxin must be present in active form
Once toxin is producing viability, microbe isn’t needed
Toxins are better able to withstand processing better than the organism
What is infection?
Caused by viable bacterial cells or viruses
Viable cells are able to multiply in the digestive tract
What are toxicoinfections?
Caused by ingestion of large numbe rof viable cells of some pathogenic bacteria
Cells either sporulate, colonize, or die, releasing the toxins
What are the human factors for illness?
Infants, old, sick, pregnant, immunocompromised more susceptible
Due to how much eaten, & how many organisms in that serving
What are the basic sources of pathogen contamination?
Processed food can gain microbes from processing environment while nonprocessed, healthy, fresh has sterile internal tissues
Natural:
- Surface of cut fruit, damaged tissues, skin, feathers, GI tract
External
- Air, soil, sewage, water, feed, human, ingredients, equipment, packages, insects
Sources of pathogen contamination in plants:
microbes on surface
present from environment (ex. raw sewage in soil)
Reduce bacterial load via:
- Treated sewage
- Washing with clean water
- Storage at low temp (if viruses there before frozen, can survive)
- Workers practice good hygiene
Sources of pathogen contamination in animals:
Carry microbes in their body
Food producing animals can carry human pathogens without showing symptoms
Meat can be contaminated from GI tract during slaughter
Dairy contamination due to fecal material on udder surafces, eggs
Reduce bacterial load via:
- Effective husbandry
- Avoid overcrowding
- Use clean food/water
- Test flocks for presence of pathogens before slaughter
- Careful removal of GI tract
- Harvest fish from clean water
What are sources of pathogen contamination from the air?
Microbes in dust & moisture droplets Mostly bacterial or mold spores, yeast, some gram + bacteria Air in highly contaminated areas can contain pathogens Reduce by: - Removing potential sources - Controlling dust particles - Using positive air pressure - Reducing humidity - Installing UV lights
What are sources of pathogen contamination in sewage?
Used as fertilizer
Particularly enteropathogenic bacteria
What are human sources of pathogenic contamination?
Carrying environmental contamination into processing plants
Sick workers
What are sources of pathogenic contamination from water?
Contaminated water
Seafood washed or maintained in contaminated seawater
use presh potable water
What are sources of pathogenic contamination from equipment?
Contaminated by any source
It then spreads the contamination to future batches
What are the factors that influence microbial growth?
Temperature
Redox potential
pH
Water activity
How does temperature influence microbial growth?
most improtant environmental factor
For every 10C rise in temperature, catalytic rate of an enzyme doubles (vice versa)
- Microbial growth is accomplished by enzymatic rxns
There is a maximal possible rate for enzymatic rxns (optimal temp)
- If it goes too high, protein denaturation & lysis occurs
- If it goes too low, membrane gelling occurs & transport processes are too slow for growth
Psychotrophs: can grow at refrigerated temps, but grow faster at room temp
How does the redox potential effect microbial growth?
Redox potential is the measurement of the potential energy difference in a system generated by a coupled rxn in which one substance is oxidized & a second is reduced (primary energy generator) Reducing agent is electron donor Oxygen in best electron acceptor Influenced by: - Chemical comp - Processing treatment - Storage conditions Fresh food spoils when cellular respiration stops & O diffuses in
What are the different types of redox potentials
Aerobes: need free O2
Anaerobes: only transfer electrons via fermentation (die in O2)
- Lack superoxide dismutase needed for O2)
Facultative anaerobes: can use free O2 or bound O2
Microaerophiles: grow better with low O2
Aerotolerant anaerobe: tolerate O2, but don’t grow in it
What are the types of atlering atmosphere packaging to preserve food?
Controlled atmosphere packaging (CAP)
Modified atmosphere packaging (MAP)
Vacuum packaging (VP)
What is controlled atmosphere packaging?
Atmosphere in storage facility is altered & gases are controlled
Expensive
Used for long-term storage for fruits & vegetables
What is modified atmosphere packaging (MAP)?
Food is enclosed in a high gas barrier packaging material
Air is removed, then gases are added & package is hermetically sealed
Stops enzymatic & respiratory activities of fresh foods
- Anaerobes can grow
Extend life of products (non-meat)
What is vacuum packaging (VP)?
Air is removed from package & package is hermetically sealed
Extend shelf life of meat products
- No gases added so anaerobes can’t grow
Why is pH important for microbial growth?
Bacteria = pH 2-3 - Gram + grow at lower pH Acidophiles = 1-4.5 Neutrophiles = 5.5-8.5 Akaliphiles = 7.5-11.5 (rare) Weak acids (have lower dissociation rate) are more problematic for bacteria
