Here is some background information by Russ Bullock from when this topic
was discussed last September. Mike Miller
"Enteric bacteria (from the Family
Enterobacteraceae, including Enterobacter, Shigella, Escherichia, and
Salmonella species) are found in soils amended with both organic and synthetic
fertility amendments (research that I have been involved with show that on
average, after amendment of soil with organic amendments such as cattle
manure, swine manure, and different kinds of composts, a spike of enteric
bacteria occurs, with between 1*10 to log 6.4-8.1, or more than 1000000 to
100000000 colony forming units, CFU, per gram of soil occurring in soils).
Often populations will decline over time in soils amended with organic
amendments, while increasing in soils amended with synthetic fertilizers, and
over studies have found no significant difference over time in soils
regardless of amendment type (1*10 to log 7.2-7.4 CFU's per gram soil). The
major point I want to make is that even in soils _never_ (to my knowledge, and
one study was conducted on experimental research stations) amended with
organic amendments enteric bacteria are _Always_ present. The major question
is whether the populations present are pathogenic to people.
For the most part, the answer must be no. If pathogenic enteric bacteria
were always present in soil, and since most soils (regardless of fertilizer
type used) contain enteric bacteria, more food-borne illnesses (on fresh
vegetables and fruit) would be attributed to them. Pathogenic enteric
bacteria are accustomed (and thrive) in the gut of vertebrates (both warm- and
cold-blooded organisms), usually with temps at 37 degrees C (for mammalian
pathogens), and an abundant food source. The soil is an oligotrophic
environment of highly variable temps and food availability, rarely meeting the
optima for growth and development needed for our pathogenic friends. Any
organic amendment (regardless of composting, although composted organic
amendments have many advantages over uncomposted manures, not the least of
which is smell) that is incorporated into the soil and left alone until
harvest (2 to 3 months for most vegetables, longer for other crops) few if any
pathogenic enteric bacteria will likely remain."
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