The control of Microbrial Growth Flashcards
Compare and contrast Sterilization vs Commercial Sterilization
Sterilization
-Destroys ALL forms of life (microorganism, spore and viruses; may or may not include prions)
Commercial Sterilization: Sufficient heat treatment to kill C. Botulinum endospores in canned food
Differentiate between Disinfection vs Antispepsis
Can a disinfectant also be an antiseptic?
Disinfection:
treatment used to Kill or inhibit microorganisms on INANIMATE objects
-Disinfectant: a chemical used for this purpose (ex: Bleach)
Antisepsis; treatment used to kill or inhibit microorganism on LIVING TISSUE
Antiseptic: chemical used for this purpose (ex: Mouthwash)
YES, a disinfectant can also be an antiseptic
what is the meaning of Cidal vs Static when discussing bacteria?
BacteriCidal: Kills bacteria
BacterioStatic: Inhibits bacterial growth
What is Degerming?
Degerming: removing microbes form a limited area
What is sanitization?
Sanitization: Reduce or Eliminate pathogenic agents on the surfaces
What is Sepsis and Asepsis?
Sepsis: The PRESENCE of toxin or pathogenic organism in blood and tissue
Asepsis: the ABSENCE of contamination by Unwanted bacteria
Explain the rate at which bacterial populations die
Bacterial populations die at a constant Logarithmic rate
one log decrease= 90% of population killed
What are the methods of controlling microbrial growth ?
Methods of Controlling microbrial growth:
Physical
-Heat
*Moist heat
*Pasteurization
*Dry Heat
-Filtratrion
-Cold
-High pressure
-Dessication
-Radiation
Chemical
What are factors that influence the effectiveness of antimicrobial treatments?
-Number of microbes
-Environmental influences:
1.Presence of organic matter often inhibits chemical antimicrobrials (ex: biofilm, bodily fluids)
2.Suspensions rich in fats and proteins protect microbes from heat treatments
3.Temperature (chemical reactions are temperature dependent
-Time of exposure
-Microbrial characteristics
What are of the actions of Microbial Control agents? What else can be damaged in the cell by these agents?
Actions of Microbial Control Agents:
Damage to the plasma membrane
-The plasma membrane is susceptible due to its lipid and protein components
-Increased permeability allows cellular content to leak into the surrounding medium
Damage to proteins and Nucleic acids
-Some microbial control agents damage pre-existing cellular proteins/nucleic acid by breaking both non covalent and covalent bonds
-Other agents interfere with synthesis of new DNA, RNA, and protein synthesis
The endozime Bio-clean (only enzymatic detergent designed to target and destroy pathogens) can also be damaged
REVIEW
How is Heat used on microorganism? Differentiate between functions of Moist vs Dry Heat
Heat
-Frequently used to eliminate microorganisms
-Moist heat kills microbes by denaturing proteins (enzymes)
-Dry heat OXIDIZES organic molecules–> Protein denaturation.
Also dries and can incinerate (destroy) cells.
define Thermal Death point (TDP), Thermal Death Time (TDT) and Decimal Reduction Time (DRT, or D value)
Heat resistance varies among different microbes
Thermal Death Point (TDP); is the lowest temperature at which ALL the microbes in a liquid culture will be killed in 10 minutes
Thermal Death Time (TDT): is the LENGTH of time required to kill ALL bacteria in a liquid culture at a given temperature.
Decimal Reduction Time (DRT, or D Value): is the length of time required to kill **90% of a bacterial population of a given temperature; D value
What are the different types of Moist Heat and how do they differ? Which method is the most effective at moist heat sterilization?
Types of Moist Heat
1) Boiling: 100 degrees C kills all vegetative bacterial pathogens, fungi + their spores and MOST Viruses within 10 minutes (usually faster)
-endospores can survive up to 20 hours
(fungi spores less resistant than endospores)
2) Autoclaving (sterilization by steam under pressure) is the MOST EFFECTIVE method of moist heat sterilization
-The Higher the pressure, the Higher the temperature
-Steam at a pressure of about 15 psi (121 degrees C) kills all organism and their endospores in about 15 mins.
(psi; pounds/square inch)
Describe the relationship between the pressure and temperature of steam at sea level. At what value of psi are most bacteria killed?
Pressure also allows liquids to reach 121 degrees C during Autoclaving
-Most bacteria are killed at 60,000 pounds per square inch (psi) of pressure
The higher the pressure (in psi; excess of atm pressure), the higher the temperature (degrees C)
How must the autoclave guage changed when operating at high altitudes? Why?
At higher altitudes, atmospheric pressure is less.
Hence to reach sterilizing temperatures (121 degrees C), and be able to kill bacteria, in a place like Denver, Colorado (high altitude), you will need autoclave gauge to be Higher than 15 psi (shown in table for pressure at sea level)
How does the Autoclave work? What are the instruments used?
An Autoclave
(machine that uses steam under pressure to kill bacteria)
-Air must be completely exhausted to reach the temperature expected for given pressure
(contains exhaust valve that removes steam after sterilization, safety valve, pressure gauge, operating valve: controls steam from jacket to chamber; Door, sediment screen, thermometer, pressure regulator (for steam supply), Steam supply, automatic ejector valve (closes on contact with pure steam when air is exhausted)
How does the container size affect the autoclave sterilization times for liquid solutions?
The larger the container size, and greater the liquid volume, the LONGER period of time is needed for sterilization time (using autoclave)
(smaller containers, reach sterilization temps faster)
When is steam sterilization most effective? Explain how dry materials are wrapped
What are other sterilization indicators are there?
Stream sterilization is the MOST Effective when the organisms are directly contacted by the steam or in an Aqueous liquid. If necessary, dry materials should be wrapped in Aluminum FOIL (trapping air in the bottom of a container is sometimes unavoidable.
Aluminum foil keeps the items “dry” (prevents the access of the steam) They will not be sterilized with the times/temperatures used for autoclaving.
Other sterilization technique: paper with endospores, that have organism that grow at high temps
What occurs in Pasteurization? What type of organisms are involved? What are the equivalent treatments used
Pasteurization
-Eliminates pathogens and reduces spoilage organisms (prolongs refrigerated shelf-life) without altering flavor
-Although many thermoduric (heat resistant) organisms survive, they are unlikely to cause disease or causes milk to spoil
- The concept of equivalent treatments
-Vat pasteurization/Low temperature long time
(LTLT); Pasteur’s original method ) 63 degrees Celsius for 30 mins
2) High temperature- short-time (HTST): 72 degrees C for 15 sec- used for most milk pasteurization today
products other than milk have their own pasteurization times and temperatures
Why do pasteurization times and temperatures vary for different food products?
Pasteurization times and temperatures vary for different foods b/c heating is less efficent in viscous foods (heating cream),and fats in foods are protective
How does dairy industry routine measure the effectiveness of pasteurization?
Dairy industry used PHOSPHATASE test (enzyme found in raw milk , that is destroyed with pasteurization)
Besides Pasteurization, how else can milk be sterilized? How does this differ in different countries?
Milk can be sterilized using Ultra High-Temperature : heated at 140 degrees C for 2-5 seconds
-milk is sterilized and Stored at Room Temperature (RT) for 6 moths-year
(some countries do not support use of this technique for milk products; meanwhile some countries have high percentage os using this system (countries like Belgium, Germany, Portugal use it; while Denmark and Greece do not.)
What are the different types of Dry Heat Sterilization? Which method has an equivalent treatment to Autoclave?
Dry Heat Sterilization
-Hot-Air Sterilization (put in oven)
-Direct flaming to a red glow (put over flame unit light is red hot)
-Incineration (burning)
The equivalent treatments:
Hot-Air; heat at 170 degrees C for 2 hours
Autoclave: heat at 121 degrees C for 15 mins (Heat transfer is faster in liquid)
(Hot-Air takes longer because heat transfers slower in air)
What methods of filtration are used to remove bacteria?
Filtration
-High-Efficiency Particulate Air (HEPA) filters: remove microbes > 0.3 um
(A HEPA air filter can reduce the amount of airborne allergens; do so by trapping harmful particles through a fine mesh)
-Membrane filtration: removes microbes >0.22 um (composed of nitrocellulose, cellulose acetate and other polymers) Now with 0.01 um pore size
-Filtration eliminates bacteria by separating the microbes from rest of liquid( sterilized medium)
What is the apparatus of membrane filtration?
Membrane filtration apparatus:
Flask of sample, membrane filter (agar) cap (of agar plate)
cotton plug in vacuum line: ensures sterility
vaccum line
In what situation is filtration the only practical way to eliminate undesirable microbes?
A solution that is Sensitive to heat and Needs to be sterilized
Explain which methods at Low Temperatures affect microbrial growth and how effective they are
Low Temperatures
1) Refrigeration- 0.7 degrees C is Bacteriostatic (stops growing) for most microbes
Psychrotrophs wil still grow slowly and eventually alter food
2) Deep freezing- renders microorganisms dormant , but does NOT necessarily kill them
-ice crystals formed during freezing disrupt cellular and molecular structure of cells (slow-freezing is more harmful than rapid)
-Survival after thawing depends on the microorganism and the time. (frozen 1 year, 1/3 to very few vegetative cells survive depending on strain)
(better to slowly thaw after freezing)
How does High Pressure affect microbial growth ?
High Pressure
Very High pressure (3-5 mins) (87,000 psi)
(deepest part of ocean is 16,000 psi) applied to a liquid suspension is instantly transferred equally through a sample food package in a flexible container (like fruit juices)
**Cell Death is linked to Denaturaion of various proteins, phospholipid gelation and irreversible damage resulting in loss of membrane, leakage **
-Can be used without heat and inactivates most vegetative cells (spore removal requires heat, low pH or pressure cycles)
-Colors, flavors and nutrient values retained.
How does Desiccation affect microorganims? What are the main two Food preserving methods? What determines Vegetative cell resistance and rank the organisms from highest to lowest resistance
Desiccation (process of drying organisms out; removing water (dehydration); microbes cannot grow or divide)
- **Metabolism is prevented in the absence of water, but cells can remain viable for years
-Lyophilization/Freeze drying can be uses as a food preservation method: coffee and fruit in dry cereal
-Air drying, which uses Warm air, is also used as a food preservation method: raisins, apples, etc
Vegetative cell resistance is Species Dependent
(ex; N. gonorrhea, 1 hr; M. tuberculosis , months)
Resistance: Endospores>vriuses>Vegetative cells
(endorses have highest resistance)
