Organisms in Soil May Protect Lettuce from E. coli
Researchers from Norway believe that naturally occurring organisms present in soil may protect lettuce from contamination by a common foodborne pathogen. Their findings appear in the May 2005 issue of the journal Applied and Environmental Microbiology.
Several recent outbreaks of Escherichia coli O157:H7 have raised concerns that contaminated fertilizer may be affecting crops of fruits and vegetables. The bacterium is commonly found in manure used as fertilizer and can survive for extended periods of time.
In the study lettuce seedlings were planted in soil fertilized with E. coli O157:H7 contaminated manure and grown for fifty days. Although the pathogen was detected in the soil for up to eight weeks, it was determined that the bacterium did not contaminate the roots, outer leaves, or edible parts of the lettuce. Pseudomonas fluorescens, a bacterium shown to inhibit E. coli O157:H7 when tested in vitro, was identified in soil found on the lettuce roots.
"In conclusion, transmission of E. coli O157:H7 from manure to lettuce was not observed when seedlings were transplanted into soil fertilized with manure inoculated with low concentrations of the pathogen," say the researchers. "The results also indicated that some of the organisms native in the soil microflora have antagonistic effects against pathogenic bacteria introduced into soil."
(G.S. Johannessen, G.B. Bengtsson, B.T. Heier, S. Bredholt, Y. Wasteson, L.M. Rorvik. 2005. Potential uptake of Escherichia coli O157:H7 from organic manure into crisphead lettuce. Applied and Environmental Microbiology, 71. 5: 2221-2225.)
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Contact: Carrie Patterson
American Society for Microbiology