disinfectant - 70% alcohol as disinfectant (Oct/26/2004 )
can anyone help me to resolve why 70% alcohol is preferred as disinfectant and sterilizing agent over absolute alcohol?
thanks in advance
Tradition and cost would be my guesses.
In fact, it is not only a question of cost as many would think!!
70% ethanol actually sterilize by precipitating the intracellular bacterial proteins, wich kills them. 100% ethanol is too strong and doesn't "have the time to enter" into the bacteria, so it only precipitate extracellular protein, and it doesn't kill it.
That's what I heard anyway!?!
Simon
70% ethanol actually sterilize by precipitating the intracellular bacterial proteins, wich kills them. 100% ethanol is too strong and doesn't "have the time to enter" into the bacteria, so it only precipitate extracellular protein, and it doesn't kill it.
That's what I heard anyway!?!
Simon
Several years ago, I saw a few sentences about this in a methods book (I think it's Gerhardt, I'm not sure anymore). 70% was shown to be more effective than higher concentrations of ethanol.
Indeed, ethanol activity is highest @ 70%. Don't know the exact reason though.
70% ethanol actually sterilize by precipitating the intracellular bacterial proteins, wich kills them. 100% ethanol is too strong and doesn't "have the time to enter" into the bacteria, so it only precipitate extracellular protein, and it doesn't kill it.
That's what I heard anyway!?!
Simon
its plain ignorance, but why doesn't 100% ethanol "have time to enter" into bacteria, when 70% can......is it the water content? cos' i can't see why 70 out of a 100 ethanol molecules (in 100% ethanol) will not enter when 70 out of 70 molecules (in 70% ethanol) can. Thanks!
If i remember correctly, it is all about dehydration of the cells. 100% will dehydrate to cell too fast and will not allow the EtOH to enter the cell.
I can confirm that. The cells dehydrate and are more or less "conserved". 100% ethanol makes the "pores" in the cell wall close very fast, as far as I know.
But you schould be carefull when you work with sporulating bacteria. I heard stories of a workmate, who could use his 70% ethanol for starting new cultures, because the spores survived this.
Absolute alcohol is not as effective as 70 % ethanol not coz it has more ethanol, coz it has less (read no) water.
See, water is an important agent used to coagulate proteins. Take this example, the egg powder is dehydrated form of egg and they say that you'll get most of the protein in it's original form back. but boiled egg is coagulated mass of albumin and the yolk. SO you understand, that water is used to COAGULATE protiens.
Why not 65% or 75%? the 70% shows best result. I'm not aware of the principle at this specific concentration.
I would assume that 70% is better than 65 or 75 due to the degree of hydrogen bonding? that is an important factor when you mix an alcohol with water