Ch.7 Controlling Microbial Growth Flashcards
what is sterilization?
removal/destruction of all living microbes
and spores and viruses
what is disinfection?
killing of vegetative pathogens on a surface
(inanimate objects); usually w/chemicals
what is antisepsis?
reduction of pathogens from living tissue
(sepsis /asepsis)
what is degerming?
removal of transient microbes from skin by mechanical
cleansing or by an antiseptic.
what is sanitation?
Relates to hygienic practices; reduction in overall total
microbial numbers to safe level
what can reduce cell numbers at a negative logarithmic rate?
exposure to antimicrobials
what happens during bariostatic treatment?
growth inhibitory
no cell killing
what happens during bactericidal treatment?
Cell killing
Cells remain intact
what happens during bacteriolytic treatment?
cell killing
cells are lysed(destroyed)
Killing occurs at what?
some logarithmic rate NOT all at once
what does the D value=?
1 minute
what is the efficacy of antimicrobial agent ?
decimal reduction time or Dvalue
what occurs during the decimal reduction time or D-value?
time for agent to kill 90% of population
what factors influence the efficacy of antimicrobial treatments?
- number/type of microbes present
- organic land
- exposure time/dose
4.pH, temperature
what are the targets of antimicrobial agents?
plasma membrane
proteins(through heat,pH or heavy metal)
nucleic acids (breakage,denaturation or chemical alteration
what are the physical agents to control microbes?
1.High temp & pressure
2.Pasterizuation
3.Dry Heat Sterilization
how is high temp used to control microbes?
-Boiling: 10 minutes @ 100⁰C
– Steam under pressure
– Autoclave: 15
psi/121⁰C/15 min
how is pasteurization used to control microbes?
mild heat; for
food/beverages
– Low temp/Long time (LTLT):
63°C/30 minutes
– Flash pasteurization; short time (HTST): 72°C/15 seconds (flash pasteurization)
– Ultra-high temperature (UHT):
140°C/>1 second
how is dry heat sterilization used to control microbes?
Incineration
Hot air-170 C 2 hr
Autoclave 121C 15 min
physical agents to kill microbes:
4.Cold Temp
5.Filtration
6.Desiccation
7.Osmotic Pressure
8.Nonionizng radiation
9.Ionizing radiation
what does cold temp do to microbes?
slows growth
what is cold temp used for?
microbial preservation
cell preservation
food preservation
what is filtered to kill microbes?
aqueous solutions and air
what uses membrane filtration?
heat liable liquids
0.45 um, 0.2 um pore sizes
what removes microbes >0.3 um?
HEPA(air)
what is the best for surface disinfection?
non-ionizing radiation
what is the effect of non ionizing radiation?
creates mutations
abnormal DNA bonds
does not peneratate well
wavelength 200-300 um
what are the effects of ionizing radiation?
DNA breakages
ionizes water to release OH
fragments nucleic acids
penetration radiation
wave length <0.1 nm
what chemical methods of control?
1.Pheonolics
2.Halogens
3.Alochols
4.heavy metals
5.surface active surfeits
6.chemical preservative
7.Gaseous Sterilants
how are phenolics used as chemical methods of control?
disrupt lipids of plasma
membrane & denature proteins.
– Remain active on surfaces after application.
how are halogens used as chemical methods of control?
alter protein synthesis & membranes
ex: iodine
chlorine bleach: oxidizing agents
what does alcohol do as a chemical method of control?
requires water
denature proteins
dissolves lipids
ex:ethanol and isopropanol
what are heavy metal use for as chemical method?
denature proteins
can be toxic–> use ay low concentration
ex:
Ag,Hg, and Cu
how are surface-active agents, and surfactants used for chemical methods?
Mimic phospholipid
structure and disrupt
membrane integrity
how are chemical preservatives used as control chemical methods?
control molds/bacteria in foods/cosmetics
– Organic acids: alter internal pH; inhibit metabolism
Ex:
* Sorbic acid, benzoic acid
how are gaseous sterilants used as chemical methods?
denature, modify proteins
ex:
– For heat->sensitive material -plastics
– Ethylene oxide
what is resistance to disinfectants dependent on?
concentration
is this true or false
Resistance more likely at lower concentrations of disinfectant
true
microbial resistance to biocides
most resistant to least resistant
prions
endospores of bacteria
mycobacteria
cysts of protozoa
negative protozoa
gram-negative bacteria
fungi, including most fungal spores
viruses without envelopes
gram-postive bacteria
viruses with lipid envelopes
what method kills endospores?
sterilization
what is the use-dilution test?
metal rings dipped in test bacteria
dried cultures are placed in disinfectant for 10 min at 20 C
rings are transferred to culture to determine whiter bacteria survived treatment
what is the disk diffusion method?
filter disks soaked in chemical agent are placed on plate inoculated with bacteria
analyze zones of inhibition (proportional to effectiveness of disfencatnt)
