Introduction Flashcards
Intrinsic factors
Factors inherent to the food (ph, water activity, nutrients)
Extrinsic factors
Factors external to the food (temp, gas, atmosphere)
Autotrophic
Carbon from CO2 through carbon fixation
Heterotrophic
Carbon from organic coompounds
Chemotrophic
Energy from chemical
Phototrophic
Energy from light
Lithotrophic
Reducing equivalents come from inorganic compounds
Organotrophic
Reducing equivalents come from organic compounds
Anaerobic terminal electrons acceptors are not found where
In food bacteria
Thermophilic
Grow at 50C or above
Thermoduric
Survive pasteurization
Psychrotrophic
Grow in fridge
Cryophilic
Grow in freezer
Halophilic
Grow in salt
Aciduric
Survive at low pH
Turgor pressure
Exists because bacteria live in environments more dilute than cytoplasm, causes a net influx of water
Gram positive
Thick peptidoglycan
Gram negative
Thin peptidoglycan, outer membrane
Teichoic acids
On gram positive
30-60% of cell weight, anchored to peptidoglycan
Lipopolysaccharide
On gram negative
Lipid A core, repeating oligosaccharide (O antigen)
Sex pili
Used for bacteria to attach to each other and transmit DNA from cell to cell
Found in enteric bacteria but not universal among bacteria
K antigen
Capsule
Repeats HMW structures to form capsule
O antigen
Lipopolysaccharide
Consist of lipid and polysaccharide; joined by covalent bond
In gram negative
F antigen
Fimbriae
Both gram neg and pos
Rarely used in classification
H antigen
Flagella
Based on reaction with the flagellin protein
5 physiological/physical states of bacteria
Vegetative, injured, VBNC, biofilms, sporulated
Injured cell
Can grow on non-selective media but not selective media
What can adding a peroxide detox to injured cells do
Help them over come damage caused by oxygen toxicity
VBNC
Cannot be cultured on any media even though viability can be demonstrated by non-culturable methods
How can VBNC viability be demonstrated
Cytological methods
Substrate responsive metabolism
VBNC is most often induced by…
A nutrient limitation
Signal transduction
Protein spans membrane, molecule binds protein and elicits response
Quorum sensing
Autoinducers diffuse through membrane to elicit response
What does auto induced mean
Signal compound is made by a gene product of the same regulon of the thing that is affected (transcribed)
Two component signal transduction consists of…
Histidine kinase and response regulator
Pleiotrophic
Occurs when one gene influence two or more seemingly unrelated phenotypic traits
Endospores
Differentiated cells that are very resistant to heat and cannot be easily destroyed
What does it mean that bacterial chromosomes are plastic
The combinations of genes present will be different in every isolate (some missing, some unique)
Core genome
Genes shared by all members of a certain group
Pangenome
Genes are present in any member of a certain group
Accessory genome
Genes that are present in a subset of members of a certain group
Prophage
Bacteriophage genome inserted into the circular bacterial DNA chromosome
Lysogenic conversion
The process by which a prophage converts a nonpathogenic bacteria to a pathogen
Defective prophage
Can no longer form infective phage because of loss of essential genes
Why can DNA elements be suspected of being defective prophages
- not common in all strains of a species
2. carry genes related to other pathogens
Plasmids
Circular molecules of dsDNA that are self replicating (in some cases linear)
What do plasmids carry
Genes which encode for products which can benefit the bacteria under certain circumstances
Insertion sequence elements
Smallest transposons, only encode the transposon, can interrupt gene function
Usually have inverted repeat on either end
Composite transposons
When two IS elements bracket other genes and and take them with them when they move
Vertical gene transfer
Transmission of DNA from mother to daughter cells
HGT
Movement of DNA from one bacteria to another
Three divisions of foodborne illness
Intoxication, infection and toxicoinfection
Intoxication
Ingestion of toxin that grew in the food
Must be present in its active form
Infection
Illness after eating viable cells
Multiply in digestive tract
Toxicoinfections
Illness after eating a large number of cells that sporulate, colonize, or die and release the toxin
Natural sources of contamination
Surface of cut fruit, damaged tissues, skin, GI tract
External sources of contamination
Air, soil, sewage, water, etc.
4 factors that influence microbial growth
Temperature, redox potential, pH, water activity
For every 10C rise in temp…
Catalytic rate of an enzyme doubles
Redox potential
Measures potential energy difference in a system generated by a coupled reaction
Something is oxidized, something is reduced
Redox potential in food is influenced by…
Chemical composition, processing treatments, and storage condition
Fresh food and plants are in a __ state because….
Reduced
BC of the reducing potential of biomolecules (when cell resp stops it changes the redox potential)
Why do anaerobes die in the presence of oxygen
They lack superoxide dismutase necessary to scavenge toxic oxygen free radicals
Controlled atmosphere packaging
Atmosphere in storage facility is altered
Hard to do
Modified atmosphere packaging
Food is enclosed in a high gas barrier packaging material; air is removed from package and flushed with gas(es)
Vacuum packaging
Removal of air and then sealed
Gas flushing
Used to extend the life of other products such as fresh pasta, bakery products, cooked eggs and fresh seafood
Most bacteria have a pH range of…
2-3 units
In general, gram pos grow at __ pH than gram neg
lower
Acids that have a __ dissociation rate are more problematic for bacteria
Lower
What has a low dissociation rate
Weak acids
Common acids used in foods
Acetic acid, propionic acid, lactic acid, citric acid, sorbic acid, benzoic acid
Citric acid
Antimicrobial activity is unclear
Aw: 0
Aw: 1
0 = dry 1 = pure water
Osmophiles
Organisms live in high sugar environments
Xerophiles
Organisms live in very dry environments
3 methods for removing water from food
Dehydration
Crystallization
Adding solutes (salt, sugar, honey, starch)
Hurdle technology
Assaults multiple homeostatic processes, most effect when it combines two stressors that act by different mechanisms
