chapter 13 - control of microbial growth Flashcards
clean (term)
relative term, doesn’t necessarily mean clean of everything
- microbial load can be reduced by washing, vacuuming, and dishwashing but is this clean enough
whether it is clean enough or not depends on the intended use of an object or surface
why clean and not sterilize everything?
- sterilization often requires time
- is labor intensive
- may degrade the quality of the item being treated
- or even have toxic effects on users
biosafety levels ranked by the severity of disease and ease of transmission
(low) BSL-1→ BSL-2 → BSL-3 → BSL-4 (high)
low-risk microbes → high-risk microbes
BSL-1
biosafety level 1: low-risk microbes
- microbes are not known to cause disease in healthy hosts
- pose minimal risk to workers and the environment
e.g. nonpathogenic strains of E. coli
BSL-2
biosafety level 2
- microbes are typically indigenous
- are associated with diseases of varying severity
- pose moderate risk to workers and the environment
e.g. Staphylococcus aureus
BSL-3
biosafety level 3
- microbes are indigenous or exotic
- causes serious or potentially lethal diseases through respiratory transmission
e.g. Mycobacterium tuberculosis
BSL-4
biosafety level 4: high-risk microbes
- microbes are dangerous and exotic
- poses a high risk of aerosol-transmitted infections, which are frequently fatal without treatment or vaccines
- few labs are at this level
e.g. Ebola and Marburg viruses
terms used to describe antimicrobial measures
- sterilization
- disinfection
- antisepsis
- sanitation
sterilization
process by which ALL living cells, spores, and viruses are destroyed on an object
disinfection
the killing or removal of DISEASE-PRODUCING organisms from inanimate surfaces
- it does not necessarily result in sterilization
antisepsis
similar to disinfection, but applies to removing pathogens from the surface of LIVING tissues, such as skin
sanitation
consists of reducing the microbial population to safe levels
- usually involves: cleaning and disinfecting an object
antimicrobials fall into 2 broad classes…
- cidal agents
- static agents
cidal agents
major class of antimicrobes
- kills microbes
bactericidal, algicidal, fungicidal, virucidal
- depending on what type of microbe is killed
static agents
major class of antimicrobials
- inhibit or control growth
bacteriostatic, algistatic, fungistatic, virustatic,
- depending on what type of microbe is inhibited
6 criteria for selection of disinfectant
1. must be fast-acting in the presence of organic materials
2. must be effective against all microorganisms without destroying tissue or acting as a toxin if ingested
3. easily penetrate the material to be disinfected without discoloration or damage
4. easy to prepare and stable in the environment where it is to be used
5. inexpensive and easy to use
6. not have an unpleasant odor
there is no perfect disinfectant that meets all criteria
microbial death curve
a logarithmic function which demonstrates the rate of microbial death
- e.g. can evaluate the degree of microbial control and to describe the progress and effectiveness of a particular protocol
several factors influence the speed at which lethal damage accumulates
1. the initial population size
- the larger the population, the longer it takes to decrease it to a specific number
2. population composition
- i.e. are spores involved?
3. concentration of agent or dose for radiation
4. duration of exposure
5. presence of organic material (e.g. blood, feces)
- ones that can inhibit disinfectant action
- organic load
can microbes be controlled without chemicals
yes, physical agents are often used to kill microbes
- or control their growth
commonly used physical control measures include…
- temperature extremes
- pressure (usually combined with temperature)
- filtration
- irradiation
high temperature and pressure ways of killing microbes
- moist heat
- dry heat
