high pressure sterilization

[Kjell]

In article <1994Sep22.133837.18968 at es.dupont.com> mccardaj at esvx17.es.dupont.com writes:
>I am doing some work using high pressure with ambient temperature for sterilizatliz
>ation purposes.  Does anyone know how high pressure kills bacteria?
>
>My original thought was that the water within the cell is highly compressed and then when the pressure is brought back down to atmospheri
>and then when the pressure is brought back down to atmospheric, it expands
>with a great deal of energy tearing apart the cell.
>
>I also thought that the cell may be under some osmotic stress.  Also,
>what about the water undergoing a phase change at high pressure and thus
>acting like a non-polar solvent?
>
>My observations have been that after high pressure treatment, the turbid 
>innoculum still appears turbid.  I would expect a clearing of the innoculum
>if the cells had actually been lysed.  I have not looked at the cells under
>a scope yet but plan to after our next run.  


>I would appreciate any discussion on the mechanism and of course if
>anyone has any good references/review articles to suggest I would be
>grateful.  I am totally new to this field and could definitely use some
>advice.
>
>Thanks,
>A.J. McCardell


I am not familiar to high pressure sterilization, and I find it 
as a  strange way of doing it. Bacteria is found at deep depths 
of the ocean so I recon they may survive 4-500 atm. Water is not 
a medium that will compress much. Think I read somewere (to long 
ago so I can't give a reference) that bacteria live as usual when 
you put pressure on them. I have also experinced that a "french 
press" not were enough to kill a culture of cyanobacteria.

Any osmotic stress may in my oppinion be to small to kill the cells
and may be ignored.

The most crucial step I think must be the drop in presure. 
Gasses (if any) will expand enourmously and this shoud be real
effective (I stress if any).

Dead cells may also be turbid I guess. 

Kjell Magne Fagerbakke
University of Bergen, Norway