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[compost_tea] E. coli and other pathogen regrowth



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First of all, there is a body of research on pathogen regrowth in composts, because there is indeed a real problem with this, and especially in large scale composting. It has been researched with respect to biosolids because of the nature of that material, and  taxpayer dollars have been spent  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 especially 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. Especially in big windrows, this means that the 'sterilized' inner portions of the piles, where the competitive microflora that would inhibit pathogen regrowth have been destroyed by overheating, are re-inoculated with pathogens that may have survived on the cooler outer surfaces when the piles are turned, and thus conditions for pathogen regrowth are created.
 
For open air composting operations seagulls and other birds can often be the source of recontamination, as can equipment that has not been cleaned between 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 microflora')
 
A too hot compost pile that has lost a large measure of its foodweb (competitive microflora) is indeed a perfect host for pathogen regrowth. A compost pile that has been monitored to prevent overheating, and has a full foodweb present, is not a perfect host for pathogen regrowth.
 
Vermicomposting destroys pathogens and unless it is thermally sterilized, will not support pathogen regrowth upon reinoculation because it relies on the 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 months of operation at our established sites. Regrowth is highly unlikely for two reasons. Firstly a high degree of stabilisation occurs. Secondly the end product is microbially active containing over 70 million beneficial soil microbes/gram on harvest and over 10 million at point of use after 12 months"
 
 
My own viewpoint is that, considering the small amounts of compost needed to produce large amounts of tea, that compost tea users growing fresh fruit and produce should use tested, clean composts of high quality; or should use composts made under cover from materials of known and contaminant free origin.
 
A compost made to process standards aimed at crashing fecal coliforms to below 1000 MPN per gram, may not be adequate to achieve the much lower OMRI standard of less than 3 CFU per gram. So a process based set of compost standards 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 thermophilic conditions, but whose pathogenicity is not known. When Dennis Avery made the claim, some years ago, that O157 was surviving hot composting, Dr Patricia 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 pathogenic 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 composting operations. Please discuss data sets that address coliform bacterial trends in thermic and vermicomposts.
 
Answer 4:
Several researchers have demonstrated that E. coli and other human pathogens can genetically adapt to the high temperatures in compost piles and survive.  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 normal heat-susceptible ones.  Recolonization of compost by pathogens can also 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.  Optimizing these conditions can help reduce the potential recolonization by pathogens. 

As far as vermicompost, Dr. Clive Edwards of Ohio State University has conducted a number of studies on the fate of human pathogens during vermicomposting.  He has extensive data to show that 30-50 day vermicomposting eliminates human pathogens".....

 

References:
Droffner, M.L., W.F. Brinton, and E. Evans. 1995. Evidence for the prominence 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 characterization of composting processes. Compost Science and Utilization 12:12-17. 

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

So there is a literature out there about E. coli that survive hot composting, 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. coli or that are made from materials that do not contain E. coli in protected environments and under appropriate parameters, eg, aerobic, not too hot but hot enough, or vermicomposted properly.
 
For many growers buying in suitable, tested composts may be a relatively cheap insurance policy and necessary for certification.
 
The use of tested recipes and equipment, and/or the subsequent testing of teas for at least a few production runs prior to use, when using untested recipes 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 filtration, 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 irrigation 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 making community to be proactive and supportive of reasonable compost standards, and to provide clear evidence in support of the science of pathogen prevention along the aerobic pathway both in the composting and the teamaking processes.
 
My two cents,
 
Frank Teuton


 
 
 
 
 
 
----- Original Message -----
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 the 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 free give the risk of re-contamination. That is, even if a compost pile is made perfectly (right temperature, adequate turning) there is always a risk that E. Coli will be reintroduced from another source such as coming in contact 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@aol.com [mailto:soilfoodweb@aol.com]
Sent: Thursday, January 30, 2003 7:08 PM
To: compost_tea@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 same 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 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.  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, clearly, by making compost correctly, getting it to temperature and keeping it aerobic, 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 matter 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 brewers 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. coli in the tea, no matter how much molasses you add - even up to 5% molasses.
------------
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, and 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 stuff right now.  Wil Brinton is correct, if you brew for longer, and don't put 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.  Compost 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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