Microbiology: Why Does 70% EtOH Work Better Than 100%?

In summary, the reason some disinfectants work better at certain concentrations, such as 70% ethanol (EtOH) compared to 100% EtOH, is because the lower concentration allows for better penetration into the microbial cell. This is important in microbiology because it can more effectively kill and dehydrate microbes. 70% EtOH also evaporates at a slower rate, allowing for better coverage of surfaces. Additionally, the balance of water and alcohol in 70% EtOH is optimal for unfolding proteins and causing damage to the microbes. Isopropyl alcohol (Iso) is also commonly used at a 60% concentration in industries and hospitals, often supplemented with caustic or peroxide. A 50:50 mix
  • #1
3
0
yea so some disinfectants work better at certain concentrations such as 70% etoh as opposed to 100% etoh.

what is the reason for this?

this is a question pertaining to microbiology btw.

thanks.
 
Biology news on Phys.org
  • #2
it's assumed to penetrate better into the microbial cel. Not aware of data to this point tho have seen data showing faster kill
 
  • #3
It takes longer to evaporate, allowing you to cover surfaces more effectively. 70% still evaporates fast as lightning, but it's more manageable.
 
  • #4
I've also heard what JorgeLobo and kingdomof mention, that it takes longer to evaporate and is thus more effective at penetrating, dehydrating, and killing microbes.
 
  • #5
You want to unfold a protein and not just dehydrate it. 95% EtOH quickly dehydrates the cell, after which the microbes can be brought back to life by re-hydration. 70% EtOH contains enough water so that dehydration is not efficient, now the protein is allowed to enter the cell and unfold proteins by the action of EtOH, this is very damaging to the microbes.
 
Last edited:
  • #6
Monique said:
The main reason is that you want to unfold a protein and not just dehydrate it.

100% EtOH acts by dehydrating the cell, after which the microbes and their spores can be brought back to life by re-hydration.

70% EtOH contains enough water so that dehydration is not efficient, now the protein is allowed to unfold by the action of EtOH and this is very damaging to the microbes and their spores.

It's actually difficult to find definitive information about this question. Ultimately it's all about contact time. Pure ethanol evaporates too quickly to be effective for the reasons explained by Monique. So all above answers are correct.
 
  • #7
This is the answer a similar question received in the Pharmaceutical Microbiology forum:

It is because alcohols become more efficient in two ways:

a) By the molecular weight (hence ethanol is more effective than
methanol);
b) the way by which alcohols destroy vegetative cells is by the
absorption
into the cell (which then causes cytoplasm leakage, denaturation of
protein and eventually cell lysis - a combination of effects sometimes
described
as membrane disruption). To be readily absorbed into the cell water is
needed.
Thus an optimal balance between the concentration of alcohol in order to
kill the cell and sufficient water to be absorbed is required. This
Comes out at around 70%. With 95% alcohol there is not sufficient water for
the bacterial cell membrane to signal that the unknown liquid can be
absorbed.

For more information, the following chapter may be of interest:

Sandle, T.: ‘Selection and use of cleaning and disinfection agents in
pharmaceutical manufacturing’ in Hodges, N and Hanlon, G. (2003;
updated 2008): ‘Industrial Pharmaceutical Microbiology Standards and
Controls’, Euromed Communications, England
 
  • #8
You'd really have to say 95% EtOH rather than 100%. That's the azeotrope.
 
  • #9
Does the disinfectant quality extend to isopropyl and water in the same fashion? I use 50:50 water and 90% Iso as a general-purpose cleaner/disinfectant around the house.
 
  • #10
turbo-1 said:
Does the disinfectant quality extend to isopropyl and water in the same fashion? I use 50:50 water and 90% Iso as a general-purpose cleaner/disinfectant around the house.

Most industries and hospitals use isopropanol at 60%. This is sometimes supplemented by caustic (NaOH) or peroxide.
 
  • #11
I got into the habit of using that mix when I was a dispensing optician. It was wonderful for cleaning lenses before and after edging the and assembling the glasses. It is a cheap no-streak cleaner for windows and mirrors, and we use it to clean countertops, especially after handling poultry.
 

1. Why is 70% ethanol more effective than 100% ethanol in microbiology?

The reason for this is because ethanol works by denaturing and coagulating proteins in bacterial cell membranes. In order for this process to occur, water molecules are needed to penetrate the cell membrane. 70% ethanol contains 30% water, which helps to facilitate this process more effectively compared to 100% ethanol, which does not contain any water.

2. Can't I just use 100% ethanol for disinfection?

While 100% ethanol may seem like a more potent disinfectant, it is actually less effective in killing bacteria compared to 70% ethanol. As mentioned before, water is needed for ethanol to effectively denature proteins in bacterial cell membranes. Without water, the ethanol cannot penetrate the cell membrane as easily, making it less effective as a disinfectant.

3. Is 70% ethanol safe to use on all surfaces?

Yes, 70% ethanol is generally considered safe to use on most surfaces. However, it is still important to follow proper safety precautions and guidelines when handling any type of chemical, including ethanol. It is also important to note that 70% ethanol may not be effective against all types of bacteria and viruses, so it is important to use the appropriate disinfectant for the specific microorganism you are trying to eliminate.

4. Can I dilute 100% ethanol to make 70% ethanol?

Yes, 70% ethanol can be made by diluting 100% ethanol with distilled water. However, it is important to use the correct proportions to ensure that the final concentration is indeed 70%. A common formula for making 70% ethanol is to mix 7 parts of 100% ethanol with 3 parts of distilled water.

5. Are there any other benefits to using 70% ethanol over 100% ethanol?

In addition to being more effective at killing bacteria, 70% ethanol also has a lower evaporation rate compared to 100% ethanol. This means that it stays on the surface longer, allowing for a longer contact time and increasing its effectiveness as a disinfectant. Additionally, 70% ethanol is less flammable compared to 100% ethanol, making it a safer option for use in a laboratory or other settings.

Suggested for: Microbiology: Why Does 70% EtOH Work Better Than 100%?

Replies
9
Views
2K
Replies
0
Views
215
Replies
2
Views
806
Replies
8
Views
1K
Replies
32
Views
2K
Replies
7
Views
1K
Replies
31
Views
5K
Replies
1
Views
852
Back
Top