Agriculture Reference
In-Depth Information
naturalize environmental niches other than intestinal tract (Ishii and others 2006).
Other reports have demonstrated that the reliability of fecal coliforms as a fecal indi-
cator in various types of foods, including fruits and vegetables, was not better than
that of
E. coli
(Dogan-Halkman and others 2003). Over the years, numerous studies
have reported that among the fecal coliforms, certain genera such as
Klebsiella
,
Citrobacter
, and some
Enterobacter
are natural inhabitants of fresh fruits and vege-
tables (Duncan and Razzell 1972; Mukherjee and others 2004, 2006b; Zhao and others
1997). This evidence suggests that, although
E. coli
can naturalize environments other
than intestinal tract, at present there is no other bacterium that could be a more reliable
substitute for
E. coli
as the fecal indicator in fresh fruits and vegetables.
Escherichia coli
Contamination in Fresh Fruits and Vegetables
A number of surveys reported the presence and counts of
E. coli
in retail samples of
fresh produce. However, comparative evaluations of
E. coli
contamination between
organic and conventional produce have rarely been reported. One recent report com-
pared overall bacterial counts and counts of
E. coli
, coliform, lactic acid bacteria,
yeasts, and molds between organic and conventional spring mix collected from a
California processor, before washing (Phillips and Harrison 2005). They found that
counts of the different bacterial groups, including
E. coli
, did not differ signifi cantly
between the organic and conventional spring mixes. Johnston and others (2005)
reported very low average
E. coli
counts in postharvest produce samples.
The large survey involving more than 3,000 retail organic produce samples reported
that only 1.5% of the produce had
E. coli
contamination (Sagoo and others 2001). A
vast majority of these contaminated samples had less than 100 CFU/g
E. coli
counts.
A smaller study on retail organic produce in the U.K. didn't detect any
E. coli
from
any of the 86 samples (McMahon and Wilson 2001). Loncarevic and others (2005)
reported considerably greater
E. coli
prevalence (8.9%) in the study on postharvest,
unwashed organic lettuce. In our previously published studies on preharvest organic
and conventional produce samples in the upper Midwest, we were able to observe
some differences in the prevalence of generic
E. coli
between organic and convention-
ally produced vegetables, but these differences were markedly infl uenced by a larger
contribution of lettuce and leafy green samples from organic farms (Mukherjee and
others 2004, 2006b). Among the different fresh vegetable types collected at farms,
lettuce and leafy greens were signifi cantly more susceptible to
E. coli
contamination.
Because of this factor, we could not conclude that any type of farm management
system was more susceptible to
E. coli
contamination.
Evaluation of Organic Practices That Could Be Linked to
Produce Contamination
Relatively limited research has been conducted to assess the risk of pathogen con-
tamination of organic management and to reevaluate the current guidelines of exist-
ing organic practices. Our research group conducted a statistical analysis on the
E. coli
prevalence results of the longitudinal preharvest testing survey conducted in
Minnesota and Wisconsin, and a few management practices used by organic farmers
were associated with increased odds of contamination (Mukherjee and others 2007).
