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Food Micro 420 Exam 2
Terms in this set (100)
Xantham gum originates from what organism?
Energy applied makes more fluid
What is an example of a Pseudoplastic product used in Food Micro?
Pickled grass = Cow food
What acid contributes most to the fermentation of Silage?
50% of people carry Staphylococcus aureus in their natural flora of what on their body?
Thicker Cell Wall/More Peptidoglycan: + OR -
What does the Cell Wall do?
Provides shape, protection from lysis, protection from chemicals, & encloses cell
Thinner Cell Wall/Less Peptidoglycan: + OR -
Dye retention in the Gram stain is clearly dependent on what structure of the cell?
In cold weather, lipids are: THICK or THIN?
In cold weather, lipids are more: UNSATURATED or SATURATED?
In warm weather, lipids are: THICK or THIN?
In warm weather, lipids are more: UNSATURATED or SATURATED?
Grow: 0 ⁰C
Optimum: 15 ⁰C or lower
Max: 20 ⁰C
Grow: 0-7 ⁰C
Optimum: 20-30 ⁰C
Max: 35 ⁰C
Grow: 15-20 ⁰C
Optimum: 30-40 ⁰C
Max: 45 ⁰C
Grow: 55 ⁰C or higher
Optimum: 55-65 ⁰C
Organism that requires oxygen for growth
Requires a small amount of oxygen for growth However:
•larger amounts of oxygen are toxic to this organism
•anaerobic environment inhibits growth
Oxygen is toxic to this organism
Does not require oxygen for growth but may use it if available
An organism that does not use oxygen in metabolic reactions but can grow in its presence
Sum total of all chemical reactions in living cells
Microorganisms breakdown large complex molecules to produce simpler molecules and release energy. Some of the energy is stored (ATP) and the remainder is given off as heat.
Microorganisms use simple molecules together with this stored energy (ATP) to synthesize complex molecules.
What unique component is found in the YEAST CELL WALL?
numerous branches under food surface (roots)
Fruiting bodies of Molds
T/F: Hyphae can be vegetative OR reproductive.
Reproductive hyphae form (Molds)
Subsurface hyphae produce WHAT to digest substrate.
Leuconostoc mesenteriodes produce WHAT while growing in sucrose.
• Filamentous Fungi
• Wide Range of Foods
Spores are formed on the BLANK hyphae.
Cross and longitudinal septa on conidia
Cause brown and black rot of fruits and tubers
What are the 4 basic methods to determine "total" numbers of microorganisms?
1) Standard Plate Count (SPC)
2) Most Probable Numbers (MPN)
3) Dye Reduction Techniques
4) Direct Microscopic counts (DMC)
Standard Plate Count (SPC) Method
1) Homogenize sample
2) Serial Dilution
5) Count CFUs (viable cells)
What do you use to homogenize food sample?
Spiral Plate Method
1) Known volume of sample is added to machine
2) Decreasing amount of sample is dispensed onto a rotating agar plate in a spiral formation
3) Count CFUs
Advantages to Spiral Plating
1) Less agar media
2) Fewer Plates
3) More plates per hour can be made
4) Little training needed
Disadvantages to Spiral Plating
1) Food particles can block dispenser stylus
2) More suited for liquid foods
3) Expensive equipment
1) Homogenized food is pre-filtered to remove large particles and then filtered again through a 0.45 um pore size filter to trap bacterial cells.
2) Cells on membrane filter can be stained
3) Cells on membrane can be placed on agar for colony formation
3 Membrane Filter Techniques
1) Direct Epifluorescent Filter Technique (DEFT)
2) Microcolony DEFT
3) Hydrophobic Grid Membrane Filter (HGMF)
Direct Epifluorescent Filter Technique (DEFT)
1) Prefiltered sample is filtered through 10 um pore size nylon filter and may be treated to lyse cells and prevent clogging
2) Filter stained with acridine orange
3) Filter dried
4) Cells counted with Epifluorescent microscopy
Advantages to Direct Epifluorescent Filter Technique (DEFT)
2) Difference is live and dead cells (Orange: Green)
3) Low # of cells can be detected
Microcolony DEFT method
1) Filter with trapped cells is placed on agar (Selection)
2) Incubation (3-6 hrs) (3= Gm -, 6= Gm+)
3) Viewed under microscope
Advantages to Microcolony DEFT
2) Results within 8 hours
Where is Streptococcus pyogenes normally found in the human body?
Back of the throat
Streptococcus pyogenes is what kind of pathogen?
Different antibodies produced
What makes S. aureus such a good pathogen?
1) Poor competitor in fresh foods
2) 50% of Humans have it present as natural flora of the nasal cavity
3) Problems in cooked foods
Blocks acetylcholine release
What human pathogen is the fastest growing at 40 oC?
Clostridium perfringens, 7 minute generation time
How does heat worsen Clostridium perfringens virulence?
1) Cooking actually "shocks" spores --> activates
2) Temp. Abuse Food
3) Eat food with lots of spores
What 4 factors are required for potentially hazardous foods?
2) Nutrient Rich
3) pH greater than 4.6
4) Support microbial growth
What pH is best for microbial growth?
Which organism has the widest pH range?
What is Water activity (aw)?
Measure of free water available for microbial growth
Lowest # of target organisms that can be detected by the method
Refers to the sensitivity of the method
Technique involving the use of a nutrient rich medium (usually a broth) that allows growth of microorganisms to detectable levels
Allows for growth of all organisms (target and background)
Allows growth of the target organism to detectable levels while inhibiting growth of the background organisms (Commonly used for Human pathogens)
Ability of a method to differentiate the target organism from a background microflora (higher specificity = fewer false positives)
A sample that tests positive by the microbiological analysis but tests negative based on cultural methods
A sample that tests negative by the microbiological analysis but tests positive based on cultural methods
Fingerprinting Foodborne Microorganism
Differentiate strains (serotypes or serovars) of microorganisms and Track the source of pathogen that caused a disease outbreak
Used to differentiate within species (use specific antibodies to identify homologous antigens)
What L. monocytogenes serotypes are disease causing outbreaks?
Serotypes 1 and 4 (4b causes 65-80% of outbreaks)
Based on high specificity of a phage for its bacterial host (phage surface receptors specific for cell's surface receptors)
How do you test for bacteriophage typing?
1) Inoculate agar
2) Mark 15-20 squares on back of agar plate
3) Drop a unique phage suspension in each square
5) Clear zone = Cell Lysis
Clear zones from cell lysis due to phage
Pulsated Field Gel Electrophoresis (PFGE) method
1) Genomic DNA from isolated pathogen digested by one or more enzymes (restriction nucleases)
2) Digested DNA added to gel well
3) Pulsed (times ramped from 1-100)
Technique for separating substances based on differences in their migration rate (differences in size)
DNA fragments (negatively charged) travels through gel toward the positive electrode (anode)
Observing differences in 16S rRNA
1) DNA extracted from pathogen linked to disease outbreak
2) DNA digested with restriction endonucleases
3) Fragmented DNA run through gel electrophoresis labeled with cDNA probe
Natural part of plant and animal tissues
Properties of the storage environment
Is pH: INTRINSIC or EXTRINSIC?
Water Activity (Aw): INTRINSIC or EXTRINSIC?
Oxidation: INTRINSIC or EXTRINSIC?
Nutrient Content: INTRINSIC or EXTRINSIC?
Antimicrobial Constituents: INTRINSIC or EXTRINSIC?
Biological Structures: INTRINSIC or EXTRINSIC?
Storage Temperature: INTRINSIC or EXTRINSIC?
Relative Humidity: INTRINSIC or EXTRINSIC?
Presence and Concentration of Gases: INTRINSIC or EXTRINSIC?
Presence and activities of other organisms: INTRINSIC or EXTRINSIC?
What is pH?
Hydrogen ion concentration
What is Water Activity?
Measure of free water available
Equilibrium Relative Humidity (ERH)
Divide ERH/100 = %
3 Ways to lower Aw of a food
1) Addition of solutes, ions, or hydrophilic
Name 5 Foodbourne human enteric pathogens that can grow at refrigerator temperatures.
1) Yersinia entercolita
2) Clostridium botulinum Type E
3) Some Strains of Bacillus cerius (Serotypes 1 and 4)
Oxidation-Reduction Potential is influenced by:
1) Chemical Composition
2) Specific Food Processing Treatment
3) Storage Condition (in relation to air)
Water is required the least for what?
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