Control of Microbial Growth Lecture Flashcards
reducing or eliminating microbial
population.
microbial control
range from complete eradication of
microorganisms to the mere inhibition of
their growth, and the goal of the
treatment will influence the control
method chosen.
microbial control
only reduces the microorganisms
boiling
- the complete removal of all life forms from a given surface by
any method. Absolute
sterilization
- Treatment of an object or surface to make it safe to handle
and free from disease transmission
decontamination
reduction in the number of pathogenic microorganisms to the
point where they no longer pose a threat of disease. s
disinfection
- Less lethal process than sterilization.
disinfection
a chemical agent used in inanimate objects.
disinfectant
- a chemical agent used in human tissue to
prevent infection.
antiseptic
used on skin
antiseptic
- removal of microbes from limited area
degerming
- kills microbes
biocide/germicide
- only inhibits growth, not killing
bacterostasis
freezing is an example of what kind of microbial control
bacteriostasis
Reduce the number of pathogens to an acceptable levels for
public health
sanitation
refers to microbial contamination.
sepsis
is the absence of significant contamination.
asepsis
Removal of pathogens from living tissue
antisepsis
techniques prevent microbial contamination of
wounds.
aseptic surgery
effectiveness of antimicrobial treatment depends on (6)
Number of microbes and microbial characteristics
§ Presence of organic load such as pus, blood,
sputum and others.
§ Time of exposure
§ Type of materials to be decontaminated.
§ Method of microbial control appropriate to the
material.
§ Capacity of the facility
material with antimicrobial properties
copper
material that is resistant to corrosion
stainless steel
most resistant to least resistant
prions
endospores of bacteria
mycobacteria
cyst of protozoa
vegetative protozo
gram - bacteria
fungi including most fungal forms
virus without envelopes
gram + bacteria
virus with lipid envelopes
when to decontaminate?
§ Before and after using equipment and work surfaces.
§ Before disposing infectious materials such as gauze, wound
dressing, syringes, disposable lab materials used in
microbiology lab.
§ Before re-using re-usable materials.
common modes of action of methods of control (3)
Damage to plasma
membrane of pathogen
(bacteria, fungi,
protozoa)
Denaturation of cellular
proteins of the pathogen
Damage to DNA of the
pathogen
physical methods of control
temperature
radiation
filtration
reduction of water activity
temp of >500C, Vaporizes organic material on nonflammable
surfaces but may destroy many substances in
the process
incineration
temp of 100 C, Thirty minutes of boiling kills vegetative forms of
bacteria but may not kill bacterial endospores.
There are also toxins that are not inactivated at
100C.
Boiling
100 C, Three 30-minute intervals of boiling, followed by
periods of cooling kills bacterial endospores.
intermittent boilding
121 C for 15 minutes at 15 p.s.i
Kills all forms of life including bacterial endospores.
The substance being sterilized must be
maintained at the effective temperature for the
entire time
autoclave and pressure cooker
160 C for 2 hours/150 C for 150
minutes.
Used for materials that must remain dry. Good for
glassware, metal, but not most plastic or
rubber items.
dry heat (hot air oven)
170 C for 1 hour
Same as above. Note that increasing the
temperature by 10 C shortens the sterilizing
time by 50 %.
Dry heat (hot air oven)
63-66 C for 30 minutes
Kills most vegetative bacterial cells, including
pathogens such as streptococci, staphylococci
and Mycobacterium tuberculosis.
pasteurization (batch method)
72 C for 15 seconds
Effect on bacterial cells is similar to batch method.
For milk, this method has fewer undesirable
effects on quality or taste
pasteurization (flash methods)
Most dependable for decontamination
autoclave
the autoclave is filled with steam to a pressure of ____ resulting in a temperature of ___
15-17 psi
121 C
hazards of autoclaving for sterilization
Explosive breakage of glass vessels during opening
and unloading.
§ Burns
§ Destruction of materials due to pressure and/or heat.
For materials that can be damaged by moist
heat or are impenetrable to moist heat.
dry heat sterilization
denatures proteins- autoclave: Steam under pressure
what kind of heat
moist heat
kills by oxidation
dry heat sterilization
reduces spoilage organisms and pathogens
pasteurization
refrigeration temperature
0-7
stops all microbial growth.
low temperature
deep freezing
Not damaging to most microorganisms
and, when brought up to suitable
temperatures, the microbes will begin
growing again.
low temperature
Microorganisms preserved in liquid
nitrogen is in what temp
-196
Destroys microorganisms with
high-energy electromagnetic
waves such as gamma rays, Xrays, UV light or electron
beams.
radiation
At high levels, ____ rays and
___ rays can denature proteins.
gamma
xrays
At lower doses, gamma rays
and X-rays collide with various
molecules (often water),
producing highly reactive
species, such as ____ and
___ radicals.
hydroxyl
hydride
uses shorter wavelengths i.e.
gamma rays, X-rays, or electron beams
ionizing radiation
Principal effect is ionization of water forming hydroxyl radicals
ionizing radiation
- UV-C irradiation at wavelength 280 to 100 nm.
non ionizing radiation
UV Radiation with longest to shortest nm
UVA
UVB
UVC
UV that causes premature aging, wrinkling of skin, implicated in skin cancer
UVA
UV that causes skin cancer, cataracts, sunburn
UVB
UV that is extremely dangerous, blocked by the ozone layer
UVC
source of radiation
cathode ray tubes
use of radiation
Sterilization and decontamination in medical supplies and
food industries.
- Food preservation
– kill by heat; not antimicrobial
what electromagnetic wave
microwaves
remove of microbes from heat-sensitive
compounds such as antibiotics and vitamins.
filtration
Physically removes microbes by employing
membranes whose pores are too small to allow
their passage.
filtration
Does not effectively remove viruses from
solution
filtration
example of filtration method control
filter sterilization
§ Uses the principle of filtration
facemasks
§ Blocks release of virus-filled droplets when you cough or sneeze.
facemasks
facemasks for COVID-19
N95 respirator mask
surgical masks
filters out 95% of the smallest particles in air
(size of 0.1 to 0.3 um)
n95 respirator masks
shield large droplets from sick person
surgical masks
used in
modern microbiology
laboratories.
membrane filter
made from polymers of
cellulose acetate, cellulose
nitrate, polycarbonate,
polyester, polypropylene or
polysulfone.
membrane filter
size of membrane filters
§ 0.01µm, 0.22µm, 0.45µm
size of high efficiency particulate air filter
0.3 um
what BSL is required for processing COVID-19 related samples
BSL-3
laboratory in DLSUD is what biosafety level
BSL-2
