PA20024 Classes Of Agent Used For Killing Microbes Flashcards
pH is a major limitation of the organic acids. What pH values will they work effectively up to?
They will only be effective at pH values up to their pKa, so can only be used up to pH values of ~5, most effective at pHs below 4.
What is the more active form of organic (weak) acids?
The undissociated, unionised form is the more active form.
Therefore pH is v.important with organic acids
What is the major advantage of organic esters over organic acids?
They’ll have good activity over a much wider pH range, they overcome the pH dependence of organic acids (their pKa is 8-8.5)
The 2 Disadvantages of organic esters?
they can take a long time to work
they can partition into the oil phase as they’re not that soluble
also they aren’t that active again gram negative bacteria
What is aliphatic alcohols optimal concentration?
70%, they have high activity at this conc, bactericidal at concentrations over 50%.
Remember aliphatic alcohols are active against mycobacteria, some of the most resistant bacteria.
Aliphatic alcohols need the presence of water to work. How do they work?
The alcohol damages the cell membrane of the microorganism, but it’s the water that gets through the membrane and lyses the bacterial cell! Alcohol just allows it to do this.
Examples; ethanol, isopropranol
Aromatic and aliphatic alcohols are less _____ than other alcohols (aliphatics)
Volatile
Therefore they don’t have as rapid killing effect, and take longer to act than aliphatics
What’s a big disadvantage of substituted alcohols? They’re _____
UNSTABLE
Advantages of using aldehydes?
They have rapid killing action
They have broad spectrum activity so kill most things
They’re not effected by organic matter
This makes them good sterilants (to sterilise things) and disinfectants, good for sterile products
What’s the deal with polymerisation and stabilising aldehydes?!
Their activation is decreased by polymerisation. We want to decrease polymerisation, as this makes them less stable, and therefore makes them more active.
You activate them with an alkalising agent ->
Which is the more active aldehyde: Orthopthaldehyde, formaldehyde or glutaraldehyde?
Orthopthaldehyde
No activation needed by alkalisation as with glutaldehyde and formaldehyde.
Not irritant, good stability
What can biguanides (eg chlorhexidine) be deactivated by?
Activity decreased by anionic compounds such as SOAP, and toothpaste (chlorhexidine in corsodyl)
One type of halogen is hypochlorite, aka bleach. It’s inactivated by ______. How is it activated?
Inactivated by organic matter
Bleach is only activated when it’s diluted with water to pH5!! It’s Stored in its inactive form.
Are iodine halogens more or less likely to get inactivated by organic matter than chlorine halogens?
Less likely!!
What are iodophores?
These contain iodine, complexed with a solubilising agent.
They allow slow release of Iodine from the complex over a long time. Eg: povidine-iodine, betadine
They MUST remain in contact with the surface for at least 2 minutes!
Which type of alcohols are often used in combo? Why?
The aromatic alcohols
They’re all active against different things eg benzyl alcohol against gram positive, phenyl alcohol against gram negative, phenoxyethanol against both..
What are acids and esters used as?
Preservatives
They’re both non toxic and cheap
Acids: food and medicines preservatives.
Esters: drugs, food and cosmetics preservatives.
What are the 3 different types of alcohols each used as?
Aliphatic: disinfectant, antiseptic
Aromatic: preservative in cosmetics, also in contact lense solutions
Substituted: preservative for pharmaceuticals and cosmetics
What are aldehydes used as?
Liquidor vapour for sterilisation and disinfection!
They have rapid kill and a broad spectrum= perfect
What are biguanides used for?
Antiseptic (remember its in corsodyl, therefore it’s killing bacteria in gum tissue)
Also a preservative
What are the halogens used for?
Liquid chlorine used for water purification and disinfection
Bleach disinfects surfaces and instruments.
Iodophores used as antiseptics before operations, to kill transient and resident bacteria.
If a lower concentration of something can be used (eg lower conc of phenyl ethanol can be used than benzyl alcohol) this means they’re more _____
Active!
More active means you can use at lower conc ☺
What is the disadvantage of silver?
It’s expensive
Also low concentrations of Ag+ ions can accumulate in cells, can lead to cell death
What is silver used for?
Antiseptic (silver nitrate in wound dressings)
Also used to decrease infection after joint replacements
The two examples of heavy metal mercurials?
Thiomersal
Phenylmercuric acetate
Are mercurials bactericidal or bacteriostatic?
Bacteriostatic
They just inhibit bacterial cell growth
Disadvantages of mercurials?
They’re toxic, irritant, and sensitive to light and air, absorbed by plastics and rubber
Plasmid mediated resistance aquired by bacteria against mercurials.
Which is the more potent biocide out of the peroxygen compounds, hydrogen peroxide or peracetic acid?
Peracetic acid
It’s active at lower concentrations
What is an advantage of the peroxygen compounds that makes them environmentally friendly?
Their breakdown products are non toxic and biodegradable,good for environment!
How do per oxygen compounds and halogens work at a cellular level?
They Oxidise their target
Oxidation can result in:
DNA or RNA Strand breakage
Degredation of unsaturated fatty acids in the cytoplasm membrane which effects its fluidity
What are phenolics (phenols) used for?
No use anymore!
What are the names of some substituted phenols? Hint: they end in ~ols
Cresols
Xylenols
Ethylphenols
Also phenolic tar acids
What are Xylenols and ethyl phenols used as?
Hospital disinfectants!
What are phenolic tar acids used as?
Household disinfectants!
How are Cresols, Xylenols and ethylphenols made more water soluble?
Solubilise them with soaps, forming a clear solution
Which kind of surfactants, cationic, Anionic, non ionic, has anti microbial activity? What are these compounds called? What does this stand for?
Cationic agents, called QACs
Stands for quaternary ammonium compounds
Used as disinfectants, antiseptics and preservatives
Nonionic, anionic, and ampholytic have detergent activity!
Advantages and disadvantages of QACs?
Water soluble, stable, non toxic, non corrosive, active at low concs, good against gram positive bacteria.
But they’re not sporicidal, their activity is decreased by organic matter.
How do aldehydes, chlorhexidine, phenols, ethanol and mercurials all kill bacteria?
By coagulation In the cytoplasm
This results in extensive cross linking and therefore proteins clumping together, disturbing the cells function and leading to death.
Formaldehyde, phenol, mercuric chloride and sodium hypochlorite all effect the ______ of the types of bacteria E___, S____,&S______
Cell wall
E.coli, staphylococcus, streptococcus
_________ work by cross linking the cell wall, of gram _____ bacteria.
Glutaraldehydes
Of gram positive bacteria
P____ and P_____ work by effecting bacterial membrane potential, meaning the bacteria can’t do any energy dependent functions, the effect the PROTON MOTIVE FORCE.
Phenols and Parabens
What agents effect enzymes in the membrane of bacteria?
Hexochlorophane: decreases electron transport
Chlorhexidine: decreases ATP synthase and ATPase
Silver and mercury : decreases enzymes with thiol groups (SH)
Cetrimide, chlorhexidine and phenol all cause _____ from the membrane as they effect permeability…
Leakage
Amino acids, purines, K+ all leak
What agent effects bacterial ribosomes?
H2O2 (hydrogen peroxide)
What effects bacterial outer membranes?
EDTA chelate ions
What effects NH2 groups by Crosslinking?
Aldehydes: Formaldehyde and Glutaraldehyde
What agents effect SH groups of bacterial DNA?
Glutaraldehyde,
Hydrogen peroxide,
Iodine
