Subject: Re: BSE - prion heat resistance

From: [email-masked] (Louis Hom)
Date: 29 Mar 1996 17:19:16 GMT

I think it was posted here that the BSE prion is stable to 120 degrees C. 
-- 
_______________________________________________________________________________
Lou Hom >K '93		       	 	  
[email-masked]  	
http://www.ocf.berkeley.edu/~lhom

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From: [email-masked]
Date: 29 Mar 1996 12:06:07 GMT

29 March 1996

Does anyone have any information regarding the heat resistance of the BSE 
agent, which is believed to be a Prion?  I have read on the WWW sites that 
these Prions are extremely heat resistant, but have not seen any 
references to literature where experiments have been done to confirm its 
resistance.

Any information, also regarding resistance to chemical agents, will be 
appreciated.

Regards

Herman
[email-masked]

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From: Grant Boston <[email-masked]>
Date: Mon, 01 Apr 1996 09:34:27 -0800

I went to a seminar last week about BSE and other transmissable SEs and 
the prion protein has been shown to be stable under 340 C dry heat for 1 
hour, 140 C autoclave for 1 hour, and 130 C dry heat for 12 hours!!! An 
amazingly strong protein especially as it's mode of action seems to 
depend on the tertiary structure.

10M NaOH will destroy it (and lots of other things)
Proteinase K removes 63 amino acids but it is unclear whether this 
destroys the protein's effects.

Grant Boston

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From: [email-masked] (Louis Hom)
Date: 1 Apr 1996 02:01:17 GMT

In article <[email-masked]>,
>depend on the tertiary structure.

It seems odd to me that they would focus so much on stability in dry
conditions.  I would expect denaturation to be much more pronounced (and
relevant) in the presence of solvent (don't we lyophilize a lot of enzymes
for added stability?). 
-- 
_______________________________________________________________________________
Lou Hom >K '93		       	 	  
[email-masked]  	
http://www.ocf.berkeley.edu/~lhom

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From: [email-masked] (Ian A. York)
Date: 31 Mar 1996 21:11:35 -0500

In article <[email-masked]>,
>conditions.  I would expect denaturation to be much more pronounced (and

They haven't just focussed on dry conditions.  Take a look in Medline,
you'll find that all kinds of conditions have been tested. I just looked
this up for a friend a couple of days ago; here's what I passed on to him
- I cut the references from here, but you can find them in Medline without
trying too hard. 
-=-
Standard approaches, such as 10% hypochlorite (bleach) and standard
autoclaving time are not completely effective: some scrapie agent survives
an hour of autoclaving, and a year (sic) of 10% hypochlorite treatment.
Higher concentrations are pretty good:  "no standard chemical or physical
decontamination procedure will reliably inactivate the amount of
scrapie/BSE infectivity present in worst-case situations but high
concentrations of sodium hypochlorite or sodium hydroxide have been shown
respectively to be completely effective or almost so." 

Autoclaving is actually much more than 99% effective, if done for longer
than an hour.  The number of infectious particles can be reduced by 10^3 -
10^7 (depending on the strain).  It is also quite effective (reduction of
titer by >10^6) if done at higher than normal temperature - at 136 oC
rather than the usual 126 oC. 

-=-
-- 
      Ian York   ([email-masked])  <http://www.panix.com/~iayork/>
      "-but as he was a York, I am rather inclined to suppose him a
       very respectable Man." -Jane Austen, The History of England

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From: Oz <[email-masked]>
Date: Mon, 1 Apr 1996 18:03:51 +0100

In article <[email-masked]>, Louis Hom
<[email-masked]> writes
>conditions.  

Perhaps because of heating during the pelleting process (for M&B meal).
Perhaps to see what incineration conditions are appropriate.

Dunno. 

It certainly makes a DNA/RNA basis for the disease problematical, I
would have thought.

------------------------------- 
'Oz     "When I knew little, all was certain. The more I learnt,
        the less sure I was. Is this the uncertainty principle?"

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From: [email-masked] (Jan Verhoeven)
Date: Wed, 03 Apr 1996 04:58:19 GMT

>depend on the tertiary structure.
snip

Grant,
Was something explained about F_values (see FAQ)?
The stated time/temp combinations
(which I presume, are autoclave saturated steam temperature and total
processing time)
could only be repeated in THAT specific autoclave used in THAT
specific experiment.
(if the other circumstances like characteristics of the sample
containing the BSE agent are identical)
If the exact time/temp recordings of the prion  ( in the same way as
temp/time recordings in jars and cans are carried out) and the sample
dimensions are known, it would clear up a lot of confusion about these
figures and  other postings on this IMPORTANT subject.

Please send me the figures and I will do some calculations.

Regards,
Jan Verhoeven Food Technologist, The Netherlands

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From: Oz <[email-masked]>
Date: Wed, 3 Apr 1996 08:31:06 +0100

In article <[email-masked]>, Jan Verhoeven <[email-masked]>
writes
>Was something explained about F_values (see FAQ)?

I can't find it there. This looks interesting.

>figures and  other postings on this IMPORTANT subject.

Do I take it that the bland statement "130C for 4 hours" hides a lot of
important information?  

As a layman in this context, I would assume that small samples would be
placed in an autoclave, a temperature sensor placed in the sample and on
it's surface and the autoclaving carried out. I would choose the sample
size so that the sample remained at the same temperature throughout and
take the time-temperature from the sensors in the sample. I would then
find out how much I had reduced the infectivity of the sample by the
treatment.

It is fairly obvious that there are other factors that would need
correcting, such as heat-up and cool-down times, but these should be
amenable to reasonable correction with the appropriate design of
equipment and a bit of maths.

One would imagine that it is then reasonably easy, by taking thermal
conduction, sample size etc, to apply this to a real situation, like a
can of beans for example.

However you comments suggests otherwise. One gets the impression that
it's more crude than this. The sample is popped in the autoclave (and it
might be a very large sample) and taken up to temperature for the
specified time. In this case "130C for 4 hrs" might result in the center
of the sample barely reaching 110C for half an hour, say. In this case
"130C for 4 hrs" is pretty meaningless.

The situation for wet samples in a dry heat situation is even worse.

The specification for "infectivity" is also, now you mention it, not as
straightforward either. 

I would genuinely appreciate your comments on this. As you say, it's
important.

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From: [email-masked] (steven h landau)
Date: Wed, 3 Apr 1996 13:28:07 GMT

[email-masked] wrote:
: 29 March 1996

: Does anyone have any information regarding the heat resistance of the BSE 
: agent, which is believed to be a Prion?  I have read on the WWW sites that 
: these Prions are extremely heat resistant, but have not seen any 
: references to literature where experiments have been done to confirm its 
: resistance.

To develop proper heat denaturation information you need to use the 
Arhenius equation.  Take samples at multiple times, and temp, to the 
math, and come up with an A & H value.

Fo and Standard bacteria kill formulas will not work well.  The Fo is 
only an approximation of Arhenius equation, which happens to be close to 
linear in the milk pasteurization/sterilzation time/temp area.

Steven Landau
Senior Project Engineer
Integrated Project Services
92 Montvale Ave
Stoneham, MA

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From: federici <[email-masked]>
Date: 4 Apr 1996 10:59:00 GMT

lyophilisation is not heating; water is eliminated using low pressure.
Concerning the use of solvents, this procedure can drive to 
denaturation, but not in all cases. For instance, it happens that 
activity of enzyme is increased in the presence of a solvent!