[USCC] O157 E Coli

Wed Dec 20 03:41:32 CST 2006

Frank,

I don't think the question of E. coli or fecal coliforms is really too
significant, one is just a sub-set of the other and [so microbiologists tell
me] the numbers aren't very different.  If there's no fecal content in the
source material there won't be much of either.  It does appear that there is
a small population in soil from wildlife, etc. - that's where 1000 fecal
coliform per gDS for Class-A came from - it's roughly the ambient
concentration.

However, I do absolutely agree with you that we need to be concerned about
phytopathogens and propagules of pernicious weeds as well.  So for Quality
Assurance purposes I would still recommend working on hitting
time-temperature.  Part of the HACCP would be to consider what is in the
feedstock and what is the intended use of the compost.  End-of-process
testing can be used as a means of control [batch release protocol] but it is
much better to have a Critical Control Point and to monitor it continuously
to check that it stays within the Critical Limits.  End-of-process testing
is then verification that the CLs are right and that there is no by-pass.

I also agree that proficiency testing schemes for laboratories are valuable,
and furthermore that they need to be blind tests, i.e. the lab should not
know when the test sample is coming or that it is a test sample when it does
arrive.  Proficiency schemes measure the competence of the labs and also the
reproducibility of the methods. It is easy to be deluded by seeing numbers
that they are different when in reality they might be the same within the
limits of precision of sampling and analysis.

regards

Tim

Dr Tim Evans
TIM EVANS ENVIRONMENT
Stonecroft, Park Lane, Ashtead, Surrey KT21 1EU England
tel/fax +44 (0) 1372 272 172 mobile +44 (0) 7816 833 991
tim at timevansenvironment.com

-----Original Message-----
From: frank [mailto:frank at compostlab.com] 
Sent: 18 December 2006 22:44
To: US Composting Council Compost Discussion List
Subject: Re: [USCC] O157 E Coli

Tim, and all

There is talk that E Coli test should replace the Fecal Coliform test 
because if one should start with a compost low in human pathogens 
(yardwaste) and it ends up as low after heating phase, it really doesn't 
matter if the temperatures got to proper temperature and time because 
there was no problem to begin with. That may be very well for public 
health reasons but IMO we need to also reduce plant pathogens like 
nematodes, sudden oak death, pine pitch and dutch elm disease and so 
many more.  I think this is better done using Fecal coliform as the 
indicator (as it is now) because there would be more starting bacteria 
and would be in all types of compost. If the heat process reduces them 
to < 1000 per gram we can be more assure both plant and human pathogens 
have been reduced.

Perhaps a process could be for a composter to test at the end of the 
heat phase, keep the compost active until they get the results back. If 
it fails, wait and retest until it passes. That way all the compost 
going to curing would have passed the test. Also; if the USCC would 
approve results from State Approved local water labs that test for FC 
all the time for drinking water the composters could test more often and 
get results back sooner without the potential problem of samples 
changing during  travel. I think instruction should be given to the lab 
doing the test to make sure the dilutions are optimized to have the 1000 
per gram range be in the section of the MPN range that is most detailed. 
We are not looking for counts - just pass/fail.

Frank

Tim Evans wrote:

>Alan,
>
>The extensive UKWIR research
>http://www.ukwir.org/site/web/content/reports/reports?SubFolders=90083&Fold
e
>rId=90078&SubFolderId=90083 showed that E. coil O157 has a similar
>thermo-tolerance to indigenous E. coli.  This was a big concern because
>there had been reports that it was more thermo-tolerant than "normal E.
>coli" but this was proved to be wrong - the earlier researchers had used a
>cultured laboratory strain as their reference and because of its "pampered"
>existence this culture was less thermo-tolerant than indigenous E. coil -
>i.e. the stuff that we healthy animals excrete every day.  The research
also
>confirmed indigenous E. coil is a good indicator for other bacterial
>pathogens and that using such as Salmonella Senftenberg is unnecessary -
>indeed I can't see how the conditions inside a microcosm used to contain
the
>S. Senftenberg can possibly mimic conditions in the bulk of the material
>being treated.  
>
>I agree with the 503 Class-A and Class-B standards and used them before
>there was anything comparable this side of the Pond. However there is also
a
>question of diligence - the dung from an animal infected with O157:H7
>contains up to log-8 E. coli per gram dry solids.  The infective dose for a
>human [with low defence] is 10[?].  If I was treating manure that could
have
>O157 I would look at the intended use [and the reasonably expected misuse]
>for the product.  Thankfully, a tiny minority of humans have O157
infection;
>the same cannot be said for farm animals so that is why I would be more
>cautious with manure than sewage sludge.  
>
>When, in 1995, I embarked on bagging biosolids composted with straw and
>selling it to gardeners via garden center retailers, I was concerned to
meet
>the highest standards and we used Class-A / PFRP.  We gave hygiene
>instructions on the bags about handwashing but it is reasonable to expect
>some will ignore this.  Also children might be around it.  We had a QA
>system for time temperature and sidelined any that did not meet it - this
>went to broad-acre agriculture small-grain cereal production.  We verified
>the QA time-temperature with E. coli testing - to verify that the Critical
>Control Point's Critical Limits were appropriate.  But, this was a 'high
>risk' use so Class-A was essential. [we could have labelled, but didn't
>"when you have handled chicken, please wash your hands before touching my
>compost" -:) ]
>
>On a note of good news, Protozoa in soil love gram negative bacteria so
when
>the E. coli, Salmonella et al. land on soil the Protozoa think "it's
>breakfast time", graze them and multiply. 
>
>regards
>
>Tim
>  
>

-- 
Frank Shields
Soil Control Lab
42 Hangar way
Watsonville, CA  95076
(831) 724-5422 tel
(831) 724-3188 fax
frank at compostlab.com
www.compostlab.com

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