[Histonet] More on Re: cleaning cryostat with 70% alcohol

[gayle callis]

There always seems to be confusion about how 70% alcohol works effectively
as a disinfecting agent for cryostats and other items.  I found an
explanation on the web, in italics below, and hopefully this will help those
for making a choice for using 70% or a higher concentration of alcohol. You
will not have bad effects from using 95% or 100% alcohol, but as far as
disinfection effects, the 70% may be better for actual killing organisms.
There is no doubt 95% or 100% is going help CLEAN the inside, but probably
not disinfect as well as the 70%.  As an aside, we have a Biosafety Level 3
laboratory where they work with Coxiella sp.  It is NOT totally killed by
NBF fixation, so after immersing tissues in NBF for fixation, they then go
into 70% alcohol which to kill the bacteria completely. They were required
to do a viability study in order to know all this, and now have to wash the
exterior of all tissues in cassettes with 70% for a specified time before
removal from the BSL3 facility. The point is they use 70% alcohol not some
higher concentration.   

  

It has to do with permeabilizing the cell wall and coagulating the proteins.
Here is the detailed explanation of for use of 70% alcohol. 

 

"As an antiseptic, 70 percent of alcohol is preferred to a stonger solution.
Pure alcohol coagulates protein on contact. Suppose the pure alcohol is
poured over a single celled organism. The alcohol penetrates the cell wall
of the organism in all direction, coagulating the protein just inside the
cell wall.  This ring of the coagulated protein would then prevent the
alcohol from penetrating farther from the cell, and no more coagulation
would take place. At this time the cell would become dormant but not dead.
under the proper condition 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 all the cell is coagulated and the organism "dies.  

 

I have NEVER seen anyone in our research labs decontaminate the numerous (at
least a dozen or more) biohoods with 100% or 95% - they use 70% on their
gloved hands, all surfaces inside and outside of the hood.  They also use
approved disinfecting agents for specific needs e.g. antiviral agents when
needed.  

 

One big complaint about using 70% inside a cryostat is the water content,
that when left on cryostat surfaces, creates an ice problem in the chamber.
We found if we dampen the gauze with 70% so it isn't dripping alcohol, we do
not get ice problems. If we find a bit of excess 70% on surfaces, we then
wipe down with 100% to help dry the surfaces. One can still leave the glass
door open to evaporate alcohol fumes.  

 

 

Personally, I have never thought nor trusted the wiping out or a cryostat
chamber was totally effective in the first place even with 70%, but merely a
daily cleaning protocol for minimizing the creepie crawlies (exception being
prions).   This is why a scheduled (weekly or otherwise) decontamination of
a defrosted cryostat is important unless your cryostat has a special
decontamination mode or procedure provided by the manufacturer.   

 

At any rate, stay safe and healthy.  If someone has a better scientific
explanation for why 70% alcohol is a better antiseptic, I would like to see
it.  

 

Gayle Callis