Lecture 8 Flashcards
What is the purpose of virulence factors?
They promote pathogenicity and are active only at optimal temperatures while dormant at cold ones.
Explain the effect heat shocking has on bacteria
Heat shocking is the process of exposing bacteria to more heat and by doing so increasing the D value or the time it takes to kill 90 percent of the bacterial population.
Why is it necessary to speed up cooling and how do you do so?
It’s necessary to speed up cooling because cooling slowly can cause more foodbourne illness than not heating properly. You can do this by placing bacteria into shallow trays rather than deep pots.
Difference between risk and hazard
Risk: Likelyhood for a foodbourne illness to occur
Hazard: The potential for a foodbourne illness to occur
How are bacteria classified based on temperature?
Mesophiles grow at warm temperatures( 20 degrees-45 degrees)
Psychotrophs: can tolerate cold(15-20 degrees)
Thermophiles grow at very high temperatures
Multiple Hurdle technology
Technology used to reduce water activity and increase acidity, increasing the number of obstacles for bacteria to grow reducing pathogenicity for longer periods of time.
How should foods be handled to analyze for microbes? What must be done before analysis?
Foods should be placed into a sterile bag containg buffer solution, homogenized by placing it into a mixer and then a pipetting 1:10 dilution of the solution.
What are common ways to analyze bacteria?
1) Aerobic plate count- can take a lot of time and requires media preperation
2) Direct microscopy- Counting microbes by looking at them
3) Flourescent staining- Uses flourescent staining to diffrentiate between living bacteria and dead bacteria in a large number of cells.
4) Bacterial metabolic processes their ability or their ability to consume various products such as sugar, starch etc. and the time it takes to do this depends upon their breakdown time
Conventional methods take 6-8 days
Rapid methods- 8 hours
1. Food sample must be infected.
2. Must be placed into growth environment
3. Time must pass before colony enumeration occurs, difficult if shelf life of food is low. So it must be done fast.
Sensitivity and Specificity
Sensitivity: The smallest number of bacterial cells that a method can detect. In most cases the lowest number or the number it can at least detect is between 10^2 to 10^5.
Specificity: The ability for a target method to ignore all other bacterial cells and only identify the presence of a specific microbe.
Required testing protocols
Pathogenic: Must be tested close to 1 cell per unit of mass of food.
Spoilage: Need more to contaminate food
Toxin: Needs to be lots to contaminate foods
What are immunologically based methods? Latex agglutination test vs. immunomagnetic test
is the quick detection of pathogens, toxins or allergens based on the presence of specific antigens that they contain which will react with specific antibodies. These are signified through
-agglutamination/clustering
-flourescent dye colorings indicating enzymatic reactions
-immuno bands
The process involves polyclonal b cells binding to multiple epitopes of a given antigen and monoclonal b cells produced bind to single epitopes on antigens.
Latex agglutination test is when beads cover food sample covered by antibody which attact specific microbe leading to agglutamation. Immunomagnetic test is the same thing as latex aglutination but this time the beads are magnetic and can remove the microbe from the antibody microbe complex.
describe some Molecular methods
PCR: Dna is extracted from cell, primers specific to microbe is used to amplify dna fragment and dna is sequenced to compare to other pathogens in database. Disadvantage: Can’t tell the difference between living or dead cell
QPCR: DNA is transcribed to RNA and removed from
cell, replicated by primers and then transcribed back to DNA. Can be used to detect the difference between living and dead cells.
