Agriculture Reference
In-Depth Information
for
E. coli
were cantaloupe (2004 and 2005, 26-32%), leaf and/or romaine lettuce
(2004 and 2005, 25-44%), cilantro (2004 and 2005, 66-71%), and parsley (2004 and
2005, 72%) (USDA- AMS - MDP 2008 ); data not shown.
A similar survey for
E. coli
on 1,183 produce items grown in Ontario, Canada, in
2004 resulted in a 0, 1.3, 6.5, 11.6, 4.9, and 13.4% reported incidence for tomato,
cantaloupe, conventional leaf lettuce, organic leaf lettuce, cilantro, and parsley, respec-
tively (Arthur and others 2007a). However, the concentrations of
E. coli
ranged from
>
5 to 7,600 and 16,000 CFU/g for cilantro and
parsley, respectively. Only two samples yielded a potential pathogen:
S.
Schwarzengrund
in a sample each of Roma tomato and organic leaf lettuce (Table 1.2) (Arthur and
others 2007a ).
Finally, a recent study of 100 domestic bagged cut spinach and lettuce mixes (con-
ventional and organic) for total bacterial, coliform, and
E. coli
counts reported means
of 7.0 to 7.7 log CFU/g,
5 to 290 CFU/g for leaf lettuce, to
<
4.0 log MPN/g and 3 to 9.2 MPN/g (16% of samples),
respectively, depending upon the product; 12.1% conventional and 16.6% organic
spinach and 23.1% conventional and 6.3% organic lettuce mix samples were positive
for
E. coli
(Valentin-Bon and others 2008). These results for bagged leafy greens from
retail markets are consistent with surveys of ready-to-eat produce in the U.S. and
other countries noted above, and other surveys reporting relatively high incidences of
E. coli
in specifi c produce items such as lettuces, parsley, and cilantro (Soriano and
others 2001 ; Froder and others 2007 ; USDA - AMS - MDP 2008 ).
Signifi cant correlations between the levels of
E. coli
contamination of produce and
incidences of major bacterial enteric pathogens are lacking. Thus,
E. coli
incidence
can be considered simply an indicator of potential minor or major preharvest contami-
nation, and a risk factor for additional postharvest contamination, cross-contamination
during washing, or amplifi cation of bacteria (pathogen) during transport and storage.
E. coli
incidence serves as a moderately effective measure of changes in fecal microbial
fl ora during the produce production and processing cycle, and for assessing the poten-
tial for pathogenic strains, if they were to be present, to survive under the same produce
processing conditions. The concentration of
E. coli
may be a more relevant indicator
of the risks associated with human consumption of a contaminated produce item.
Evidence of fecal contamination as high as 50-70% on some produce items does
not correlate necessarily to a higher incidence of illness, unless undetected sporadic
illness is occurring. Although major outbreaks are of concern, it should be empha-
sized that relative to the number of consumptions of ready-to-eat produce (and tree
nuts) (many billions), outbreaks are not frequent, causing an extremely low number
of known total cases per total consumptions; however, some cases are sporadic prob-
ably and never linked to a food source. Nevertheless, vigilance and research are
important to identify what is probably a rare convergence of events and/or specifi c
circumstances that result in a major outbreak of disease, some of it severe, and thus,
a noticeable event. The relatively low incidence of pathogens on produce measured
in surveys seems consistent with the speculation that incidence is very rare and
occurs only after multiple unusual circumstances that result also in an outbreak.
Surveys of produce are informative because they provide a measure of the back-
ground incidence of indicators of fecal contamination and pathogens related to
dynamic spatial, temporal, and geographic factors. Incidence in the absence of illness
or outbreaks also is informative.
<
0.5 to
>
