[compost_tea] E. coli and other pathogen regrowth

From: Frank Teuton <fteuton_at_sympatico.ca>
Date: Mon, 3 Feb 2003 14:02:00 -0500

MessageFirst of all, there is a body of research on pathogen regrowth in co=
mposts, because there is indeed a real problem with this, and especially in=
 large scale composting. It has been researched with respect to biosolids b=
ecause of the nature of that material, and taxpayer dollars have been spen=
t looking at the problem.

See for example the extensive discussions in The Science and Engineering of=
 Composting, Hoitink and Keener eds, 1992, Renaissance Press. See especiall=
y the Farrell piece and his discussion of Yanko's work.

Large compost piles often reach high temperatures, high enough to crash the=
 populations of mesophilic organisms and 'quasi-sterilize' the piles. Espec=
ially in big windrows, this means that the 'sterilized' inner portions of t=
he piles, where the competitive microflora that would inhibit pathogen regr=
owth have been destroyed by overheating, are re-inoculated with pathogens t=
hat may have survived on the cooler outer surfaces when the piles are turne=
d, and thus conditions for pathogen regrowth are created.

For open air composting operations seagulls and other birds can often be th=
e source of recontamination, as can equipment that has not been cleaned bet=
ween use for windrows well along in the process, and windrows in the early =
stages with high populations of pathogens.

Smaller windrows, in vessel systems, static pile systems, and flow through =
vermicomposting systems, properly managed, should offer better alternatives=
 for the production of high quality composts with a full foodweb present to=
 inhibit and resist pathogen regrowth. (Full foodweb, aka 'competitive mic=
roflora')

A too hot compost pile that has lost a large measure of its foodweb (compet=
itive microflora) is indeed a perfect host for pathogen regrowth. A compost=
 pile that has been monitored to prevent overheating, and has a full foodwe=
b present, is not a perfect host for pathogen regrowth.

Vermicomposting destroys pathogens and unless it is thermally sterilized, w=
ill not support pathogen regrowth upon reinoculation because it relies on t=
he competitive microflora entirely throughout the process. See

http://www.vermitech.com/why.htm

"No pathogen regrowth has been detected in any resampled material over 30 m=
onths of operation at our established sites. Regrowth is highly unlikely fo=
r two reasons. Firstly a high degree of stabilisation occurs. Secondly the =
end product is microbially active containing over 70 million beneficial soi=
l microbes/gram on harvest and over 10 million at point of use after 12 mon=
ths"


My own viewpoint is that, considering the small amounts of compost needed t=
o produce large amounts of tea, that compost tea users growing fresh fruit =
and produce should use tested, clean composts of high quality; or should us=
e composts made under cover from materials of known and contaminant free or=
igin.

A compost made to process standards aimed at crashing fecal coliforms to be=
low 1000 MPN per gram, may not be adequate to achieve the much lower OMRI s=
tandard of less than 3 CFU per gram. So a process based set of compost stan=
dards that were designed to acheive the less than 1000 MPN/g EPA biosolids =
standard may not guarantee acheivement of OMRI performance standards.

The study Elaine references below is a Chinese bench sized in vessel study =
which operated at below the required 55 C temperature requirement and still=
 found destruction of E. coli 0157:H7 after two weeks.

Other researchers have found strains of E.coli that could adapt in thermoph=
ilic conditions, but whose pathogenicity is not known. When Dennis Avery ma=
de the claim, some years ago, that O157 was surviving hot composting, Dr Pa=
tricia Millner of the USDA-ARS and other researchers pointed out that this =
was not known to occur. (I will refrain from saying that the survival of pa=
thogenic E. coli in thermophilic composting was 'hotly denied'.....;-)

See:

http://www.aste.usu.edu/compost/qanda/toxins.htm

"Question 4:
Heat tolerant strains of E. Coli are reported to develop in thermic compost=
ing operations. Please discuss data sets that address coliform bacterial tr=
ends in thermic and vermicomposts.

Answer 4:
Several researchers have demonstrated that E. coli and other human pathogen=
s can genetically adapt to the high temperatures in compost piles and survi=
ve. Some have survived temperatures as high as 65 degrees C. What is not =
well known is the pathogenicity of these genetic variants relative to the n=
ormal heat-susceptible ones. Recolonization of compost by pathogens can al=
so occur from sources outside the pile and from the cool edges of the pile.=
  Researchers have identified three factors which influence recolonization =
- moisture content, carbon availability, and microbial diversity. Optimizi=
ng these conditions can help reduce the potential recolonization by pathoge=
ns.
As far as vermicompost, Dr. Clive Edwards of Ohio State University has cond=
ucted a number of studies on the fate of human pathogens during vermicompos=
ting. He has extensive data to show that 30-50 day vermicomposting elimina=
tes human pathogens".....



References:
Droffner, M.L., W.F. Brinton, and E. Evans. 1995. Evidence for the prominen=
ce of well characterized mesophilic bacteria in thermophilic (50-70 degrees=
 C) composting environments. Biomass and Bioenergy. 8:191-195.

Brinton, W.F., and M.W. Droffner. 1994. Microbial approaches to characteriz=
ation of composting processes. Compost Science and Utilization 12:12-17. =
 

Soares, H., B. Cardenas, D. Weir, and M. Switzenbaum. 1995. Evaluating path=
ogen regrowth in biosolids compost. BioCycle. June 1995, p. 70-75.
**********************************************

So there is a literature out there about E. coli that survive hot compostin=
g, and of E. coli regrowth in composting.

This literature would seem to support a 'precautionary principle' approach =
to compost tea, namely, to use composts that either test negative for E. co=
li or that are made from materials that do not contain E. coli in protected=
 environments and under appropriate parameters, eg, aerobic, not too hot bu=
t hot enough, or vermicomposted properly.

For many growers buying in suitable, tested composts may be a relatively ch=
eap insurance policy and necessary for certification.

The use of tested recipes and equipment, and/or the subsequent testing of t=
eas for at least a few production runs prior to use, when using untested re=
cipes and equipment, would seem to be minimally prudent for anyone using CT=
 on fresh fruit and produce for raw consumption.

Water quality is also an issue, and pond and well water might need either f=
iltration, UV treatment, or ozonation, to eliminate pathogens in some cases=
, before using it in tea production.

Rumor has it that New York vegetable growers using well or pond water for i=
rrigation of raw consumption produce may be required to use a UV system to =
ensure pathogen destruction.

Given that kind of thing in the regulatory pipeline, it behooves the tea ma=
king community to be proactive and supportive of reasonable compost standar=
ds, and to provide clear evidence in support of the science of pathogen pre=
vention along the aerobic pathway both in the composting and the teamaking =
processes.

My two cents,

Frank Teuton









  ----- Original Message -----
  From: Bennett Valley Vineyards at WebQuarry
  To: compost_tea_at_yahoogroups.com
  Sent: Saturday, February 01, 2003 10:23 AM
  Subject: RE: [compost_tea] Any Comments or reply to this?


  I was at the Compost Tea presentation at Eco-Farm and wanted to correct t=
he assertion made in this post.

  At the Eco-Farm meeting, in California, it was reported to me by at least=
 three people, that the person speaking in the Compost Tea session from BBC=
 Lab (Bess' lab in Arizona) said that E. coli will be present in compost no=
 matter what.

  The presenter did not say it would be present no matter what, but that it=
 is almost impossible to garauntee that any compost pile would be E. Coli f=
ree give the risk of re-contamination. That is, even if a compost pile is m=
ade perfectly (right temperature, adequate turning) there is always a risk =
that E. Coli will be reintroduced from another source such as coming in con=
tact with equipment that has been recently been in contact with a new pile.=
 One re-innoculated, the compost pile is a perfect host.

  Again, she did not say this happened every time but that it could happen =
and that there was a real risk of E. Coli in any compost pile and that what=
 we needed was on site testing.

  Peter
    -----Original Message-----
    From: soilfoodweb_at_aol.com [mailto:soilfoodweb_at_aol.com]
    Sent: Thursday, January 30, 2003 7:08 PM
    To: compost_tea_at_yahoogroups.com
    Subject: Re: [compost_tea] Any Comments or reply to this?


    Thank you, Matt, for a much more sane reporting on what went on at the =
Viticulture meeting.

    When I read the post from the BD Now person, I wondered if the people I=
 knew that had gone to the meeting and had talked to me had gone to the sam=
e meeting as that person was talking about.

    The bottom line, in my opnion, is that Vicki Bess overstresses E. coli =
danger. At the Eco-Farm meeting, in California, it was reported to me by a=
t least three people, that the person speaking in the Compost Tea session f=
rom BBC Lab (Bess' lab in Arizona) said that E. coli will be present in com=
post no matter what. If you add molasses to compost tea, E. coli will grow=
 to high number.

    Now we all read on SANET a few weeks ago, in a nicely documented study,=
 that if compost is properly composted, it will have no E. coli. So, clear=
ly, by making compost correctly, getting it to temperature and keeping it a=
erobic, there will be no E. coli surviving.

    If you don't have E. coli in the compost, it won't be in the tea. No m=
atter how much molasses you add, if there is no E. coli in the compost, it =
won't grow in the tea.

    We have data, and we keep repeating the experiment in different tea bre=
wers to show which ones make good tea, given the same compost, same recipe,=
 same water etc. In all the tea makers, no E. coli in the compost, no E. c=
oli in the tea, no matter how much molasses you add - even up to 5% molasse=
s.
    ------------
    The point about addition of food resources to tea is a very good one. =
If you add too much food, the organisms get too happy, grow really fast, an=
d make the tea go anaerobic.

    Why do you add foods to tea? So you can have a finished product in 24 =
hours, or maybe less. Typical American impatience - we have to have our st=
uff right now. Wil Brinton is correct, if you brew for longer, and don't p=
ut additional foods in the tea, the tea usually doesn't go anaerobic. Good=
 deal, huh?
    ---------------
    But there is one point about which no one is right about so far. Compo=
st tea was "invented" by the Romans. At least as far as we can tell. Cato=
, in his book "De Agriculturia" was the first WRITTEN book on agricultural =
processes. What does he describe in that book? Basically, the production =
of compost tea. So, the inventor of compost tea was some peasant farmer in=
 ancient Rome. Everything from then has merely refined the process.

    Elaine Ingham
    President, Soil Foodweb Inc.
    www.soilfoodweb.com

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Received on Mon Feb 03 2003 - 23:41:40 EST

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