control of bacterial growth Flashcards
define sterilization
complete killing of all living microbes including spores
define contamination
treatment of objects or surfaces to make them safe to handle
define disinfection
control of pathogens on inanimate objects
define antisepsis
control of pathogens in living tissues
define sanitization
process to lower microbial loads
define ‘cidal’ biocides or germicides
they kill microbes
- bactericide (bacteriocide)
- fungicide
- viricide
define ‘static’
they do not kill microbes but inhibit growth
- bacteriostat
- fungistat
- -viristat
define sepsis
bacterial contamination
define asepsis
absence of bacterial contamination
what are some of the factors influencing the effectiveness?
- # of mirobes
- environmental conditions
- time of exposure
- microbial characteristics
define the mode of action: alteration of membrane permeability
leaks cellular contents
define the mode of action: damage to proteins
denaturation
define the mode of action: damage to nucleic acids
damaged DNA or RNA will interfere with cell division and protein synthesis
what are 3 physical ways to kill bacteria
- heat
- radiation
- filtration
what is the most common method to kill bacteria?
heat
what does heat do to bacteria?
denatures proteins
what is the thermal death point?
the lowest temp at which all microbes in a particular suspension will be killed in 10 min
what is moist heat?
boiling at 100 C (10-15 min)
does moist heat kill spores?
no
what is steam under pressure (autoclave)
steam at 15 psi raises temp to 121 C
does autoclave kill spores?
yes
how do you know if the autoclave is done?
autoclaving tape
what is pasteurization?
0heat sensitive liquids( milk, fruit jiuce, etc)
- intended to kill pathogens
- lowers bacterial numbers and prolongs shelf life
how do you pasteurize something?
high-temp, short time (HTST)
72 C for 15 sec
how do you do ultra-high temp pasteurization?
milk is heated to 140 for 3 sec
is dry heat as effective as moist heat?
no
what is flaming?
sterilization of inoculating loops
what is incineration
contaminated materials and carcasses
what is hot-air sterilization?
heating at 170 C for 2 hours
-used for glass wares
what is radiation?
electromagnetic waves: microwaves, Xrays, gamma rays, etc
- ionizing
- nonionizing
what is ionizing radiation?
wavelength
what is nonionizing radiation?
- wavelength >nm
- UV rays
- damages DNA by causing bonds to form between thymine (thymine dimers)
do microwaves have much antimicrobial activity?
no, other than the effect of heat generated
what is filtration?
sterilize heat sensitive liquids
- membrane filters used to exclude bacteria
- High efficiency particulate air (HEPA) filters are used in hospitals and labs
what was the first chemical used as a disinfectant?
phenol
what do we use now instead of phenol?
phenolics (derived from phenol, less irritant and more effective)
what is the mode of action of phenol and phenolics?
disruption of cytoplasmic membrane
what chemical is used as a standard to measure the effectiveness of all disinfectants?
phenol
what are the standard organisms used as standards for testing disinfectants?
salmonella typhi and staphylococcus aureus
what is the chart for phenol coefficient
1 = same as phenol >1 = more effective
what compounds are halogens?
iodine and chlorine
-effective antimicrobial compounds
what is one of the oldest and most effective antiseptics?
iodine
what is tincture of iodine?
iodine in aqueous alcohol
what is iodophore?
iodine complexed with an organic molecule for slow release (betadine)
what happens to chlorine in water?
becomes hypochlorus acid (HOCl), which is a strong oxidizing agent
what do alcohols kill?
people… and vegetative cells, but not the spores
What is the mode of action of alcohol?
denature proteins and disrupts cytoplasmic membrane by dissolving lipid
which is more effective, isopropanol or ehtanol?
isopropanol
what heavy metals are disinfectants?
silver, mercury, copper and zinc
what heavy metal is used as an algaecide in water troughs?
copper sulfate
what heavy metal is used in foot baths?
zinc chloride
what are surfactants?
surface active compounds
-soaps and detergents
how do soaps work?
-no antiseptic action, but mechanically remove bacteria due to scrubbing
what are used in cleaning dairy utensils and equipments?
acid-anionic surface active compounds
what are quaternary ammonium compounds?
cationic detergents
- more effective against gram +
- no effect on spores
benzalalkonium chloride and cetylpyridinium chloride are what?
quaternary ammonium compounds
what are some oxidizing agents?
-ozonem hydrogen peroxide, benzyl peroxide and peracetic acid
what is ozone used for?
disinfecting water
why is hydrogen peroxide not useful in infected open wounds
it is rapidly broken down to water and o2 by catalase
where is hydrogen peroxide useful?
in deep wounds caused by anaerobes because released o@ would kill them
when is benzoyl peroxide useful?
in treating wounds infected by anaerobic bacteria
what does peracetic acid kill?
spores
what is used in the food processing industry and in disinfection of medical equipment?
Peracetic
what are aldehyde’s mode of action?
inactivate proteins by forming covalent bonds with amino acids
what is formalin used for?
to inactivate bacteria and toxins in vaccine preparation
what is glutaraldehyde used for?
bactericidal and sporicidal
what is ethlene oxide used for?
- gaseous sterilizers
- effective against all microbes and spores but requires several hours
what is the mode of action of ethylene oxide
denatures proteins
what is ethylene oxide used for?
sterilizing medical equipments
-suspected carcinogen
