high pressure sterilization

greenera at wmvx.lvs.dupont.com greenera at wmvx.lvs.dupont.com
Fri Sep 30 07:52:22 EST 1994

In article <1994Sep29.135409.14710 at es.dupont.com>, mccardaj at esvx23.es.dupont.com writes:
>In article <35v2vd$7pv at alf.uib.no>, Kjell Magne Fagerbakke writes:
>>In article <1994Sep22.133837.18968 at es.dupont.com> mccardaj at esvx17.es.dupont.com writes:
>Main point from previous article:
>>>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 t
>>>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
>>>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
>High pressure sterilization is used in cases where the traditional means of steri
>sterilization are not amenable to the item being sterilized, such as something
>that would melt at high temps in an autoclave.  I also know of some work using h
>high pressure to sterilize certain foods, such as fruit to be put into yogurt.
>Please could someone explain to me what a "french press" is?  This is the 
>second reference to it and I have no idea what this is.
>I like your idea about the most crucial step being the drop in pressure.  
>Yes, dead cells can be turbid too, but not lysed ones?  My point was that I
>was expecting the cell to be lysed and therefore the suspension clear.  
>We have had a fair amount of success to date with everything but those nasty sp
>spores, specifically Bacillus stearothermophilus.  
>I am still hoping to generate more discussion on how high pressure affects the 
>bacteria.  By what mechanism(s) does it actually kill cells?

>Most bacteria are normally turgid (internally pressurized) because
they contain a far higher concentration of dissolved materials than
their environment. They are protected by their cell walls from
being disrupted by their internal pressure and usually are quite
insensitive to variations in osmotic effects. If the cell wall is
removed, say by lysozyme treatment, the protoplasts are easily
lysed osmotically.

A French press is a biochemist's gizmo for disrupting cells without
preparing protoplasts and may be the original inspiration for
studies of high pressure sterilization. It has a small chamber
(usually about 1 cubic inch or so) into which the cell suspension
is placed. A machined lid is put on the chamber and the whole
thing is placed in a mechanical press. The contents are pumped
up to very high pressures and then the pressure is rapidly released
by opening a valve. After several cycles of this, the cells are
disrupted and you can isolate your enzyme or whatever. The amount 
of disruption can be followed by looking the microscope.

Sorry I can't recommend any particular references, but there is
an extensive literature on the effects of high pressure on bacteria
going back at least to the sixties. In addition to sterilization,
researchers have been interested in marine bacteria from the
ocean depths which normally live at high pressure and sometimes
die if the pressure is reduced. I'd suggest looking through some
Annual Reviews of Microbiology for a review article.

Good luck.

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