23 replies to this topic

[josse]

Hallo,

why do we use 70% ethanol to disinfect?

I always assumed it was because 70% was the lowest dosage that was still working (the more you dilute, the cheaper it is). But is this even true?

I have heard someone saying that 70% is the % that works the best against bacteria etc..
But why does 70% work the best? And why not 80%?


I find it hard to believe that 100% would work as well or even better then 70% to kill of germs..

[gebirgsziege]

EtOH dissolves lipids of the cellular membrane. But many organisms have a cell wall constiting of proteins and carbohydrates, that are not dissolved by EtOH. When you mix EtOH with water, the EtOH will still reach the lipid layers and the cells can be killed. 70 % is the percentage that proved to be most effective against microbes, therefore we use 70 %.

[Adrian K]

gebirgsziege, on 22 November 2010 - 07:04 AM, said:

EtOH dissolves lipids of the cellular membrane. But many organisms have a cell wall constiting of proteins and carbohydrates, that are not dissolved by EtOH. When you mix EtOH with water, the EtOH will still reach the lipid layers and the cells can be killed. 70 % is the percentage that proved to be most effective against microbes, therefore we use 70 %.

Hi gebirgsziege,
I find it very hard to search for literature regarding the mechanism of EtOH in killing microbes.
Do you know or can you suggest any?
Thanks.

Adrian

[Ameya P]

gebirgsziege, on 22 November 2010 - 07:04 AM, said:

EtOH dissolves lipids of the cellular membrane. But many organisms have a cell wall constiting of proteins and carbohydrates, that are not dissolved by EtOH. When you mix EtOH with water, the EtOH will still reach the lipid layers and the cells can be killed. 70 % is the percentage that proved to be most effective against microbes, therefore we use 70 %.

Although, I agree with what you say (and believed in this thoery until an year ago), it has been proven (somewhere in the 70s- 80s) that 100% ethanol is the most effective against microbes. There is of course a paper for this, which I have read and am having trouble in relocating right now. Shall get back to you, when I find it.... but the fact is that 100% ethanol is most effective.

[gebirgsziege]

@ adrian kohsf: sorry no literatur, this was what I learned at several labs and courses at the university, and never felt the need to doubt this knowledge as 70% EtOH works perfectly.

@ gt_ameya: would be interesting to read the paper, thank you for the information. But even 100 % EtOH does by far not kill all microbes - e.g. you can place some fungi in 100 % (or given the hydrophilic nature of EtOH 96 %) EtOH some of them still are able to grow after some days. But one of the effects is that using diluted EtOH mixed with water is very good to clean surfaces from all kind of contamination (e.g. fat, dust, sedimented airborne microbes etc) where microbes adhere, and it is less toxic than many other disinfectants. And a clean surface is a bad environment for microbes.

Edited by gebirgsziege, 22 November 2010 - 11:32 PM.

[chimaera]

AFAIK the optimal working range of alcohols as disinfectants is 60 - 95%, but optimal concentrations may vary dependent on the bacteria you are trying to kill.

[Ameya P]

gebirgsziege, on 22 November 2010 - 11:31 PM, said:

@ gt_ameya: would be interesting to read the paper, thank you for the information. But even 100 % EtOH does by far not kill all microbes - e.g. you can place some fungi in 100 % (or given the hydrophilic nature of EtOH 96 %) EtOH some of them still are able to grow after some days. But one of the effects is that using diluted EtOH mixed with water is very good to clean surfaces from all kind of contamination (e.g. fat, dust, sedimented airborne microbes etc) where microbes adhere, and it is less toxic than many other disinfectants. And a clean surface is a bad environment for microbes.

I am still searching for the paper. I guess I will have to approach my previous supervisor. I remember my first day at his lab and he said that 70% ethanol is most effective (cause his supervisor had said so) and I had asked him why not 100%. So he spent that day trying to answer the question and came back with this paper and admitted that his supervisor and he himself were wrong all these years..... thats why I remember it so well.

Well the reason, all labs use 70% ethanol might be what you said, can remove dust, fat etc. and saves a bit of money too. Just a thought, could it also be that 100% ethanol evaporates, while ethanol in water takes longer to evaporate (thats the theory I came up with in the last 30 secs   )

[Ameya P]

Both of you, gebirg and chimaera have joined the forum on d same date....

[gebirgsziege]

gt_ameya, on 23 November 2010 - 09:31 PM, said:

Both of you, gebirg and chimaera have joined the forum on d same date....

Yes like many many others here, this was the day after the big bioforum breakdown    when all data of two or more years of bioforum were lost. Luckily enough most of us came back again the day bioforum was restored  

Don't mind the paper, if you stumble over it again just remember to post it here, we will find it. I thought about the explaination I learned and found some weak points, like when bacteria live in water the will dissolve their cell wall if it really is that soluble in water. But still we will keep using 70% EtOH, for most of the above mentioned reasons.

Edited by gebirgsziege, 23 November 2010 - 11:16 PM.

[pito]

gt_ameya, on 22 November 2010 - 09:18 PM, said:

gebirgsziege, on 22 November 2010 - 07:04 AM, said:

EtOH dissolves lipids of the cellular membrane. But many organisms have a cell wall constiting of proteins and carbohydrates, that are not dissolved by EtOH. When you mix EtOH with water, the EtOH will still reach the lipid layers and the cells can be killed. 70 % is the percentage that proved to be most effective against microbes, therefore we use 70 %.

Although, I agree with what you say (and believed in this thoery until an year ago), it has been proven (somewhere in the 70s- 80s) that 100% ethanol is the most effective against microbes. There is of course a paper for this, which I have read and am having trouble in relocating right now. Shall get back to you, when I find it.... but the fact is that 100% ethanol is most effective.

If you should find that paper.. pls post it..

Would be usefull for me too.

[hobglobin]

There was once a long thread here about this topic, seems as if it was in the old forum.
Anyway: The book "Disinfection, sterilization, and preservation" by Seymour Stanton Block (Lea & Febiger, 1991) has a chapter about alcohols (chapter 12) and their concentrations and mode of actions. You can (at least here) read it partly in google books, or your library has it.
And here a link to a short text

[Ameya P]

After much search, I ended up troubling my supervisor, who was kind enough to give me the title and author of the paper. As it turns out, it was published in 1950 (before my supervisor was born) and is called THE RELATIONSHIP OF CONCENTRATION AND GERMICIDAL EFFICIENCY OF ETHYL ALCOHOL
Harry E. Morton.

Google helped me land on the following link.
http://onlinelibrary...1944.x/abstract

But I can't access it from here.... and it will be nice, if some one sends it back to me.... I promise to treasure it this time....  

Edited by gt_ameya, 24 November 2010 - 11:25 PM.

[gebirgsziege]

gt_ameya, on 24 November 2010 - 11:23 PM, said:

But I can't access it from here.... and it will be nice, if some one sends it back to me.... I promise to treasure it this time....  

see your pm!

[Adrian K]

Hi, gebirgsziege,
can I have that as well? Thanks.

[Adrian K]

Hi hobglobin, I too uses 80%~85% alcohol on bench. Is there any way that I can get the chapter in PDF? my library doesn't have it...
Thanks.