MICR221 Lecture 5 - Chemical Control Methods (NOT FINISHED) Flashcards
what are the 3 chemical control methods for controlling microbial growth?
disinfectants
antiseptics
preservatives
what is the purpose of chemical control methods?
used to reduce the number of microbes to acceptable numbers instead of physical control methods
what are disinfectants?
chemicals that are capable of killing microorganisms but can not be applied to living tissue
where are disinfectants applied in the lab?
applied to inanimate surfaces and used in discard jars + buckets
what are antiseptics?
chemical agents that kill or inhibit the growth of microorganisms that are sufficiently non-toxic enough to be applied to living tissues
what are preservatives?
substances or chemicals that are included in pharmaceutical preparations or foods to prevent the microbial spoilage of the product
when are disinfectants used?
disinfection of equipment occurs when equipment can not be sterilised by other methods (e.g physical control methods)
what is the primary use of antiseptics?
used for antisepsis of the skin
how do the chemical control methods of disinfectants, antiseptics and preservatives kill cells in terms of rate of cell death?
they all do not simultaneously kill all or cells or instantly kill all cells, they kill the cells at constant rate
what are the 10 conditions that influence the effectiveness of antimicrobial agents?
population size properties of the chemical agent (dilution + pH) type of microbe phase of growth of the microbe polymer, capsule or lipid production altered cell wall/membrane/modified sensitive sites cellular aggregation/biofilms resistant structures microbial interactions environment factors
how does population size influence the effectiveness of antimicrobial agents?
population size influences as only a fraction of the microorganisms die during a given time interval. The time it takes to achieve sterility/reduce the microbes to acceptable numbers depends partly on the number of organisms present at the beginning of sterilisation
e.g if 90% of the bacterial population is killed during the first minute then approx. 90% of those remaining will be killed during the next minute and so on
what is the relationship between a large population and the time required to achieve sterilisation through chemical control methods?
as the rate of cell death is constant it will take longer to kill all members of a larger population than a smaller one which is why the initial bacterial load is minimised
how does the properties of a chemical agent influence the effectiveness of antimicrobial agents?
the properties of a chemical agent include dilution and pH. Chemicals have an optimal concentration therefore they cant be too concentrated or too diluted.
e.g the activity of ethanol is enhanced in the presence of water as it functions best at 70% ethanol + 30% water
Microbes have an optimum pH and chemicals can cause unfavourable pH changes resulting in cell death
how does the type of microbe influence the effectiveness of antimicrobial agents?
the type of microbe influences the effectiveness as some microbes are better suited to different methods of chemical control and this varies between microbes
`how does the phase of growth influence the effectiveness of antimicrobial agents?
the exponential phase is the most effective phase to kill, as cells during this phase have an increased metabolic rate causing a larger uptake of chemicals compared to the stationary phase
