Hi,

a) 70% ethanol has been found to be most effective in killing microbes. Higher or lower concentrations are not so effective in killing microbes.

b) if you use 90% or absolute ethanol, it will evaporate fast and may not be much effective.

Cheers, Nadine

Dear Riyazulla,

70% percent of alcohol is ideal to a stronger solution. Pure alcohol coagulates protein in contact. Suppose the pure alcohol is poured over a single celled organism. The alcohol will go through the cell wall of the organism in all direction, coagulating the protein just inside the cell wall. The ring of the coagulated protein would then stop the alcohol from penetrating farther from the cell, and no more coagulation would take place. At this time the cell would become inactive but not dead. Under the favorable conditions the cell would then begin to function. If 70 percent of alcohol is poured to a single celled organism, the diluted alcohol also coagulates the protein, but at a slower rate, so that it penetrates all the way through the cell before coagulation can block it. Then the entire cell is coagulated and the organism dies.

Regards

Amir

Hello!

The effectivity of ethanol as e.g. desinfectant or antiseptic agent depends on the concentration of ethanol-water-mixture: An ethanol percentage of 50-80% destroys the cell wall/membrane of bacteria by denaturing their proteins and dissolving their lipids (effective against most bacteria, fungi and some viruses; ineffective against bacterial spores). Therefore, the ethanol has to pass the bacterial membrane/wall to get into the bacteria - if you use 100% ethanol instead, the bacteria get 'sealed' and they will survive... An other mechanism is the high osmotic pressure of ethanol/water-mixtures; and the 70% has the highest one.

Regards.

Simon

Thanks all for your valuable suggestion thank you once again

But why not 75%, which is used more commonly in hospital

Methanol is too much toxic to us. So not used I think. 

b) 90% ethanolwill evaporate fast

c) An ethanol percentage of 50-80% destroys the cell wall/membrane of bacteria by denaturing their proteins and dissolving their lipids. Effective against most bacteria, fungi and some viruses; ineffective against bacterial spores. Therefore, the ethanol has to pass the bacterial membrane/wall to get into the bacteria - if you use 100% ethanol instead, the bacteria get 'sealed' and they will survive... Another mechanism is the high osmotic pressure of ethanol/water-mixtures; and the 70% has the highest one.

d) Less expensive

e) Safer flammability level

 Many colleagues have already pointed the importance of using between 50%-80% Ethanol instead of using 100%. I will just add that the percentage is a product of research on the best percentage dilution of ethanol with water for killing pathogens because 100% ethanol is not very effective. As Xiaohua Wuke question, yes some hospitals use 75% and there are usually variations in the percentage but all are likely to fall within the 50%-80% range.

70% is more effective against mycobacteria - Best, M., Sattar, S.A., Springthorpe, V.S. et al. Comparative mycobactericidal efficacy of chemical disinfectants in suspension and carrier tests. Appl Environ Microbiol., 1988; 54: 2856–8

70% alcohol has been found to effective in sterilizing lab bench work area, killing microbes and other contaminants. Its mode of operation is by cell protein denaturation, destruction of cell wall/membrane of the microbes in question as it slowly permeate into cell thereby inhibiting its growth. important is the high osmotic pressure of 70% alcohol than its highest concentration (100%) or lower form. cheers.

Methanol is not particularly effective at killing bacteria, compared with ethanol. In addition, IPA (iso-propyl alcohol) is generally more effective than ethanol. The following article may be of interest: http://www.americanpharmaceuticalreview.com/Featured-Articles/184449-Pharmaceutical-Facility-Sanitization-Best-Practices-Considered/

Amir Haider, could you recommend some article with this mechanism

let's not forget to mention that the 70% (+/-)alcohol is only effective on the vegetative cell, not the endospore or spore .

Hye, but then how about the effect of volume alcohol and contact time on bacterial growth? For instance 70% alcohol pad/swab product apply on skin before injection.

the 70% (+/-)alcohol is only effective on the vegetative cell, then what is effective on the endospore or spore？

70% ethanol is the minimum concentration when used in a lab setting for aseptic technique. You don't want to go lower, because it will not kill the microorganisms you are trying to kill.

Commonly, 70% ethanol is use to wipe bacteria infected place/platform for maintain aseptic/sterile condition. Because, 70% ethanol will affect the cell wall of bacteria as well as affect the growth and multiplication strongly. Also one of reason is ethanol and water combination will create osmotic pressure.

Hello

If you are using it for cleaning , then the 70% is so that there is a dehydration effect on the bacteria, thus killing the bacteria.

https://www.ncbi.nlm.nih.gov/pubmed/25405882

Good Luck

Agreed with all answers however one thing I want to add is the contact time which is required for alcohol to kill the cell. If we use 100% alcohol it will evaporate quickly so the time required for alcohol to show its effect will be reduced, similarly for diluted one the contact time will be increased but the minimum toxic concentration which is required for cell death will not be achieved. hence at 70% we get the best results.

Muhammad Samie

Because 70% ethanol is bactericidal. This concentration of ethanol able to kill most of the microbes in short time.

Quite simply, 70% empirically was determined to be the most effective.

Ali Bustan Mohsen Al Waaly

"70% ethanol is the minimum concentration when used in a lab setting for aseptic technique. You don't want to go lower, because it will not kill the microorganisms you are trying to kill."

70% is not the minimal. It is the optimal.

Also keep this in mind high concentration can also damage the skin so cannot be used as antiseptic for living tissue.

Autoclaving and high intensity UV lights also should not be used for living tissue.

Impossible to get 100 percent ethanol It absorbs water from air 90 percent is possible without elaborate packaging

Michael h Hayman standard is 96% ethanol as that is the concentration when ethanol-water form azeotrope. But 100% ethanol may be achieved through various means.

Years ago, it was explained to me very simply... The alcohol denatures the lipids in the cell wall - basically poking holes in the microorganism. The 30% water can then enter, and lyse, the cell. It's like when your nose bleeds on clothes, plain water will make the cells burst, but if you make a saline solution, the cells will wash off the fabric, in tact. That's how I explain it to non-scientists :)

yes, this is all true, but every one should be careful during formulation, time of contact is important, how much it takes time to kill, 70-75% ethanol with layer creating material is suitable.

Concentrations above 20% alcohol are sufficient to show the cidal effect. The question is duration in which this happens effectively.

https://www.cdc.gov/infectioncontrol/guidelines/disinfection/disinfection-methods/chemical.html

it precipitates protein and DNA of microorganism, and hence can kill microorganism, just like we use alcohol in protein isolation and DNA isolation procedures

Ethanol at 70% can dissolve the lipid cover, pass through and disintegrate the proteinous structure. Lower conc. inadequate to dissolve the lipid, higher conc. coagulates the proteinaceous cover and prevents ethanol from disturbing MO RNA/DNA. This is important in case of virions (SARS-Cov-2) with thick lipid coat. Also to correct the erroneous consideration that colognes are disinfectant because the highest degree cologne is 80 degree, which means 40% ethanol

70 percentage ethanol is good for inactivating the SARS-Cov_2. But in Bangladesh Absolute ethanol (99.9 Per) is difficult to find. Really they are not like absolute. May be 95-96 per. Therefore when we prepare the hand sanitizer, pls consider this point. Wish you good health during this emergency period of nCovid-19.

Ethyl alcohol is indeed virucidal against both lipophilic and hydrophilic viruses. Max potency occurs at 70%

All the explanations are possible, but nobody did show a scientific assay for the declarations.

agree with Md. Anowar Hossain

I accept Amir

Ethanol poorly migrates inside the cell. Due to the properties of the "dipole" called H2O, this migration is improved.

Short-term exposure of bacteria to ethanol will cause only its surface (protein, lipids) to denature and create a protective layer, ethanol will rapidly evaporate and bacteria will rebuild the cell wall.

In addition, ethanol is more expensive than water, nevertheless- concentration less than 60% (ethanol / water) does not work satisfactorily.

Summarizing:

- water increases ethanol migration inside the cell,

- water reduces evaporation of the disinfectant,

- 70% of the agent is cheaper to produce than 99%

100% ethanol completely coagulate the outer cells proteins and it works as defense mechanism in the cells of organism but in case of 70% ethanol, the ethanol does not completely coagulates the proteins of the cell hence penetrates in the organisms body and it dies. So the area becomes contamination free.

Because 100 pc ethanol is highly volatile and thus is lost rapidly where as the 70 pc ethanol can retain for little longer and is enough to alter the osmoticum of bacterial cell wall/membrane..

at70%concentration the ethanol does not evaporate quickly comparing with it at 100% so that give alcoholic enough time to enter the microorganism and destruction cell and that lead to kill

And what about the disinfectant efficacy and usage of 20% ethanol?

From CDC

"Their (ethyl alcohol and isopropyl alcohol ) cidal activity drops sharply when diluted below 50% concentration, and the optimum bactericidal concentration is 60%–90% solutions in water (volume/volume)."

https://www.cdc.gov/infectioncontrol/guidelines/disinfection/disinfection-methods/chemical.html#

However you can buy it and was also suggested by some people to use it instead of 70% ethanol in cell culture work.

https://www.merckmillipore.com/INTL/en/product/Ethanol-200-0,MDA_CHEM-480910

https://www.thistlescientific.co.uk/product/20-ethanol-cleaning-spray/

This concentration can kill almost all types of microbes present on the surface area.

Dear Riyazulla Azeez and all respected colleagues,

The question was crystal clear, he questioned about sanitizing the working area NOT the mechanism or microbicidal activity of the ethanol if I'm not mistaken. As we know, 80-100% of ethanol evaporates quickly and that might be not enough to eradicate all microorganisms on the working place. While lesser concentration needs a longer time to evaporate since in the Lab we are in a rush to do this and that and must assure that the working surfaces are sanitized well to perform other Lab works. So 70% is just perfect to kill all microbes and saving time.

Primary efficacy of ethyl (and isopropyl) alcohol is thought to be a function of nonspecific denaturation/coagulation of protein, not dehydration per se and efficacy is established in tens of seconds or less. An essential element is cleanliness of the surface. Alcohol efficacy diminishes greatly on soiled surfaces.

Methanol is much inferior to ethyl and isopropyl alcohols for disinfection. Superior efficacy at 70% (+/-) is empirical =and though to be a matter of penetration and solvency.

https://www.cdc.gov/infectioncontrol/guidelines/disinfection/disinfection-methods/chemical.html

Tilley FW, Schaffer JM. Relation between the chemical constitution and germicidal activity of the monohydric alcohols and phenols. J. Bacteriol. 1926;12:303-9.

Morton HE. The relationship of concentration and germicidal efficiency of ethyl alcohol. Ann N.Y. Acad. Sci. 1950;53:191-96.

see chapters on alcohol as disinfectant Block's books - the latest.

McDonnell, G., 2020. Block’s Disinfection, Sterilization, and Preservation. Lippincott Williams & Wilkins.

This have to do with water activity. At 70%, Ethanol tend to be better compared to 90% because the water helps the disinfectant to stay longer on the bacteria cell, thus giving it more time to interact/Disrupt normal 'Life' process of the bacteria

Owolabi Oluwafemi Akinkunmi

Can you provide data supporting your water activity (Aw) concept?