Saturday, March 13, 2010

When E. coli On Produce Cannot Be Washed Off

No matter how much care food processors take to prevent bacterial contamination of produce, if the water and soil in which the plant is grown is contaminated, the plant may be too ... inside.

Here are two studies that demonstrate:

1. Association Of Escherichia coli O157:H7 With Preharvest Leaf Lettuce Upon Exposure To Contaminated Irrigation Water, Journal of Food Protection, January, 2002

Researchers added E. coli to the growing medium (soil or hydroponics) of lettuce. The bacteria adhered to the plants' roots allowing internalization through roots, stomata, cuts, or bruises.
"These data suggest that preharvest crop contamination via contaminated irrigation water can occur through plant roots."
2. Interaction Of Escherichia coli With Growing Salad Spinach Plants, Journal of Food Protection, October, 2003

Researchers inoculated spinach seeds with E. coli, grew them in soil, and found E. coli on the leaf surfaces and roots 42 days later:
"E. coli was recovered from the external surfaces of spinach roots and leaves as well as from surfacesterilized roots."
Researchers also grew 20-day old plants hydroponically in an E. coli-infused medium. They found E. coli associated with the roots after harvest, even after surface sterilization, "indicating that it had been internalized."

A positive finding...

Seedlings grown in soil inoculated with E. coli (opposed to hydroponically) resisted uptake of the bacteria. Authors speculated:
"Competitive microflora in soil may have restricted root colonization by E. coli."
So - organic or locally grown, thoroughly washed after harvest - these should not instill peace of mind if the water, soil, and fertilizers (e.g. manure) used to grow produce are themselves contaminated. And in the case of E. coli O157:H7, you only need about 10 bacterium to infect and cause illness. (See 100,000 Fit On A Pin Head; Only 10 Needed To Kill.)

Photo of a local farm in Maryland by Dylan Slagle of the Carroll County Times. Caption:
"Organic liquid fertilizer recovered from poultry production is applied by injection to a grainfield on the Snader farm in Marstan July 15 [2009]."
The backstory on this particular farm is contentious and shines a light on the problem of what to do with the rising tide of excrement originating from the rising tide of livestock farms that supply the rising tide of humans their rising demand for meat.


Angela and Melinda said...

That's very interesting about hydroponic vs soil. Re manure on organic farms, no responsible farmer uses raw manure, but only fully composted manure. However, as we all know, many "organic" farms are organic in name only, adhering to the minimal letter of the law and not the spirit.
Doesn't the aging, composting process (in which considerable heat builds up) kill the bacteria in manure (which of course should only be from herbivore animals anyhow)?

Bix said...

Composting reduces levels of bacteria. It doesn't eliminate them. From Richardson's article:

"The major difference between Class A [Biosolids] and Class B is the amount of fecal coliforms present in the sludge. While it's lower in Class A, studies show it regrows in the compost after the treatment process is over."

ElDoubleVee said...

The sludge still has use though it may not be for food production. Why not use it as fertilizer for crops not consumed, like for crops raised for bio-fuels or trees for renewable sources of wood. It isn't useless.

Bix said...

Growing trees for wood. You know, that's not a bad idea.