Week 7 Flashcards
What chemical/physical agents are used to control growth of MO’s?
Heat
Radiation
Toxic chemicals
Microbial growth helps
curb the transmission of infectious microbes
Examples of microbial growth control practical applications
- routinely wash fresh fruits and vegetables to remove attached microorganisms
- inhibit microbial growth on body surfaces by washing.
Sterilization
killing or removal of all microorganisms (including viruses)
* In many circumstances, sterility is not required.
Decontamination
the treatment of an object or surface to make it safe
to handle
Disinfection
a process that directly targets pathogens although it
may not eliminate all microorganisms.
Disinfection Requires
agents called disinfectants
that actually kill microorganisms or severely
inhibit their growth.
Where is microbial growth control used extensively?
Industry
Medicine
Home
What are 3 classes of physical controls?
- Heat: is the most widely
- Radiation
- Filtration
How is effectiveness of heat as a sterilant quantified?
By decimal reduction time (D)
What is Decimal reduction time?
The time required at a given temperature for a 10-fold reduction in
the viability of a microbial population.
What is the relationship between D and temp?
exponential
What are the types of heat?
- Moist heat has better penetrating power
- Dry heat.
Temperature
heat killing proceeds more rapidly as the
temperature rises.
What is thermal decimal time?
- Another way to characterize the heat sensitivity of an organism
- The time it takes to kill all cells at a given temperature.
How to determine thermal decimal time?
Samples of a cell suspension are heated for different times, mixed with
culture medium, and incubated.
* Is independent of the original cell number
* A longer time is required to kill all cells in a large population than in a
small one.
What factors influence the effectiveness of heat?
- The presence of endospore-forming bacteria in a heat-treated sample can influence both the decimal reduction and thermal death times.
- The medium in which heating takes place
* This is especially relevant in food canning procedures.
an endospore is?
- very dehydrated
- contains calcium dipicolinate
- contains small acid-soluble spore proteins (SASPs) that help confer heat stability on the structure.
pH
Microbial death is more rapid at acidic pH, and acidic foods such as tomatoes, fruits, and pickles are easier to sterilize than neutral-pH foods such as corn and beans.
High concentrations of sugar, proteins, and fats do what?
decrease heat penetration and usually increase the resistance of organisms to heat
High salt concentrations do what?
may either increase or decrease heat resistance, depending on the organism.
What is an autoclave?
a sealed heating device that uses steam under pressure
to kill microorganisms
What temp kills endospores?
endospores requires heating at temperatures
above the boiling point of water at 1 atm.
who discovered pasteurization?
Louis pasteur
How does pasteurization work?
At the temperatures and times standardized for the
pasteurization of food products, all known pathogenic
bacteria are killed.
What is flash pasteurization?
To pasteurize milk, the liquid is passed through a tubular heat
exchanger. Careful control of flow rate and the size and temperature of
the heat source raises the temperature of the milk to 71°c for 15 sec
(or even higher temperatures for shorter time periods after which it is
rapidly cooled.
what does pasteurization do?
uses heat to significantly reduce rather than
totally eliminate the microorganisms found in liquids, such
as milk.
Physical microbial killing agents
- Heat
- Radiation
- ultraviolet (UV) light, X-rays, and gamma rays
- Filtration
What does radiation need to be between to kill exposed organisms?
220 and 300 nm
What is UV radiation useful for?
disinfecting surfaces and air
Where do we use UV radiation in day to day life?
▪ to decontaminate and disinfect the work surface of laboratory laminar
flow hoods equipped with a “germicidal” UV light
▪ air circulating in the hospital
▪ food preparation rooms
What is poor with UV radiation
poor penetrating power, limiting its use to the
disinfection of exposed surfaces or air
What is ionizing radiation
is electromagnetic radiation of sufficient energy
to produce ions and other reactive molecular species from
molecules with which the radiation particles collide.
The unit of ionizing radiation
Roentgen
The standard for sterilization
the absorbed radiation dose,
measured in rads (100 erg/g) or grays (100 Gy=100 rad)
X-rays or gamma rays
have sufficient energy and penetrating power
to kill microorganisms in bulk items such as food products and
medical supplies.
Radiation is used to sterilize these pieces in lab/life
- surgical supplies
- plastic labware
- Drugs
- even tissue grafts
- certain foods and food products such
- fresh poultry
- meat products
- spices
When is filtration used?
Heat-sensitive liquids that are not sterilized by radiation are typically
sterilized by filtration.
what is the average filter pore size
0.2 μm average size is a
minimum requirement
What are the several types of filters are in routine use in microbiology
depth filters
*membrane filters
*nucleopore filters.
What are depth filters?
a fibrous sheet made from an array of overlapping paper
or glass fibers that traps particles in the network of fibers
What are membrane filters
- The most common filters used for liquid sterilization in the
microbiology laboratory - Composed of high-tensile-strength polymers
manufactured in such a way as to contain a large number
of tiny pores.
What are nucleopore filters
A type of membrane filter
* Made from a thin polycarbonate film that is treated with
radiation and then etched with a chemical, yielding very
uniform-sized holes.
What are nucleopores commonly used for?
to isolate
specimens for scanning electron microscopy.
cidal agents
Agents that actually kill are called -cidal agents, with a prefix indicating the type
of microorganism killed
* Bactericidal agent
* Fungicidal agent
* viricidal agent
static agents
Agents that inhibit growth are called -static agents,
* bacteriostatic agent
* Fungistatic compounds
* viristatic compounds
what is an AMA
natural or synthetic chemical that kills or inhibits the
growth of microorganisms.
Antibacterial agents are classified as
-static, -cidal, or -lytic
bacteriostatic agents
typically inhibitors of some important biochemical process
* bind relatively weakly
* if the agent is removed, the cells can resume growing.
* Some antibiotics, such as the sulfonamides, work in this
way.
* The clinical value of bacteriostatic antibiotics is their ability
to keep a pathogenic bacterium from multiplying until the
immune system can rid the body of the pathogen.
Bactericidal agents
bind tightly to their cellular targets and by definition kill the
cell.
* the dead cells are not lysed, and total cell numbers,
reflected in the turbidity of the culture, remain constant.
* for example formaldehyde
Bacteriolytic agents
kill cells by lysing them
* affects both viable and total cell numbers
* Example:
* detergent that ruptures the cytoplasmic membrane
* the antibiotic penicillin, which inhibits bacterial cell wall
synthesis, resulting in cell lysis.
What is the minimum inhibitory concentration (MIC)
determining the smallest amount of the agent needed to
inhibit the growth of a test organism
What is one way to determine MIC of a given agent
inoculate a series of tubes of liquid growth medium
containing a test organism and dilutions of the agent.
