Lecture 1- Food is an Ecosystem Flashcards
Anaerobic Metanogens
Eat CO2
Phototrophs
Eat sunlight/CO2, produce O2
Anaerobic Metanogens
Make CH4
Aerobic Methanotrophs
Eat CH4
Aerobic Methanotrophs
Makes CO2
Ecosystem
is a series of interactions between the environment and the organisms that inhabit it
Food ecosystems are composed of intrinsic and extrinsic factors. What are intrinsic factors?
Factors inherent to the food (pH, water activity, nutrients)
Definition of extrinsic factors
Factors external to the food (temperature, gaseous atmosphere)
What is the usual growth of bacteria (think of graph)
Lag phase: plateau
Log, or exponential growth, phase
Stationary phase
Death, or logarithmic decline, phase
Autotrophic
Carbon from CO2 through carbon fixation
Heterotrophic
Carbon from organic compounds
Mixotrophic
can combine auto and heterotrophy
Chemotrophic
energy is obtained from external chemical compounds
Phototrophic
energy is obtained from light
Lithotrophic
reducing equivalents come from inorganic compounds
Organotrophic
reducing equivalents come from organic compounds
Aerobic organisms
use O2 as a terminal electron acceptor (this is the most energetically favorable reaction)
Fermentation
use organic carbon as a terminal electron acceptor, therefore, fermentative organisms are considered anaerobes
Facultative anaerobes
an organism that can grow with or without oxygen
What are the 4 things that bacteria need to have to grow and divide?
- Must have carbon for building the array of chemical substances of which they are composed (anabolism)
- Bacteria must have a source of energy for living (catabolism)
- Must have a source of electrons to be used in energy conservation and biosynthetic reactions
- Must have an electron acceptor
Denitrification
nitrate as an electron acceptor
Sulfate Reduction
sulfate as an electron acceptor
acetogenesis
CO2 as an electron acceptor
Lactic Acid Bacteria
Produce large quantities of lactic acid from CHO
Proteolytic Bacteria
hydrolyze PRO in food because they produce extracellular proteinases
Lipolytic bacteria
hydrolyze TGs because they produce extracellular lipase
Termophilic bacteria
bacteria that are able to grow > 50C
Thermoduric Bacteria
able to survive pasteurization temps
Psychrotrophic bacteria
able to grow at refrigerated temps (<5C)
Cryophilic bacteria
able to grow at freezer temp. (<0C)
Halophilic bacteria
able to survive high salt concentrations (>10C)
Aciduric bacteria
able to survive low pH
Osmophilic bacteria
able to grow at a higher osmotic environment
Spore formers
able to produce spores
Coliforms
used as an index for sanitation
fecal coliforms
used as an index for sanitation, presence indicates fecal contamination
enteric pathogens
can cause gastrointestinal infection
What organism is the main issue when meat is stored chilled?
psychotropic organisms like listeria
What organism can be present in heat processed meats like lunch meat?
Since these products can be stores anaerobically, pychrotrophic facultative anaerobes may dominate
What type of organism is responsible for spoilage in non-temperature abused milk?
Psychrotrophs
Why can microorganism grow rapidly in fish?
fish have high water availability, pH of the tissue, and the availability of C and N
What pH must you can your food for it to be safe from Clostridium?
lower than 4.6
Can staphylococcus toxin survive the canning process?
Yes, toxin can survive the process of canning and cause food poisoning following the consumption of the product
Injured cells
more sensitive to selective agents (antibiotics) and may have increased nutritional requirements
Microbial injury is important in food microbiology for several reasons (3)
- If injured cells appear dead due ti the use of selective media in thermal studies, the thermal resistance will be underestimated and the true “kill” values will be low
- Injured cells make escape routine detection post-processing leading to faster spoilage or a safety problem
- the “selective agent” may be a common food ingredient such as salt, organic acid, or suboptimal temperature
Viable But not Culturable (VBNC) and examples
VBNC- a state in which cells cannot be cultured on any media even though their viability can be demonstrated by non-culturable methods
It is a survival strategy for non-sporulating species
During transition rod shaped cells shrink and become spherical bodies
EX: Salmonella, Campylobacter, E.coli, Shigella, Vibrio
How do you demonstrate that the cells are still viable through cytological methods? (3)
- Structural integrity of the bacterial cytoplasmic membrane indicated life, while deterioration of this membrane indicates that the cell is dead
- Fluorescent nucleic acid strains (red) are incubated with cells, if they permeate the cell it indicates the cell is dead
- Counter stain is used to stain the cell wall (green). Bacteria with intact cell membranes stain free, whereas bacteria with damaged membranes stain red
How doe you demonstrate that the cells are still viable through substrate responsive metabolism? (2)
- Cells can be incubated with a nutrient and an antibiotic that inhibits cell division
- live cells elongate, but do not divide
Can VBNC be resuscitated? If so, how?
Yes, by temperature shifts and a gradual return of nutrients.
Cellular communication: Signal Transduction
two component regulatory systems where one PRO spans the membrane, picks up a signal and then reacts based on a response regulatory PRO
Who uses it?: L monocytogenes, S.aureus, Lactic acid
Cellular communication: Quorum Sensing
Systems are built on autoinducers which diffuse through the cellular membrane to initiate a specific response when a certain population density has been reached
Who uses it? S. enteric, E.coli, V. cholerae
Pleiotrophic
occurs when one gene influences two or more seemingly unrelated phenotypic traits
Biofilms
aggregation of cells, often of multiple species, into heterogeneous complex structures that are attached to a solid surface
More resistance to heat, chemicals and sanitizers the planktonic cells, making them imp. to the food industry
Endospores
differentiated cells that are very resistance to heat and cannot be easily destroyed, even by chemicals
