Agriculture Reference
In-Depth Information
(2/28), and 68% (82/120) (Harris and others 2003). In contrast, all 214 samples of
lettuce or salad mix tested for
E. coli
O157:H7 in large U.K. and U.S. studies were
negative (Harris and others 2003). Of
3,800 ready - to - eat salad vegetables from retail
markets sold in the U.K., only 0.2% were positive for
Salmonella
; an additional 0.5%
were considered of poor quality due to contamination with
E. coli
or
L. monocytogenes
at
>
100 CFU per g of product (Sagoo and others 2003). A survey of “minimally pro-
cessed” vegetables in Brazil determined that 4 of 181 samples (2.2%) were contami-
nated with
Salmonella
(Froder and others 2007). Similarly, 180 fresh vegetable
samples surveyed in South Africa identifi ed 4 (2.2%) contaminated with
E. coli
O157:H7, and reported levels of
E. coli
O157:H7 as high as 1,600,000 CFU/g of
spinach (Abong'o and others 2008). These results refl ect the tremendous diversity
of produce quality depending upon spatial and temporal factors, and possibly
methodological factors.
Multiple outbreaks of
Salmonella
illness associated with tomatoes have occurred
recently, but surveys of tomatoes for the incidence of pathogens have been limited.
Of 123 samples of domestic (U.S.) tomatoes tested by the U.S. FDA-CFSAN starting
in May, 2001, none were positive for
Salmonella
or
E. coli
O157:H7 (FDA - CFSAN
2001b); also, 0/20 imported tomato samples collected starting in March, 1999 were
negative for both pathogens (FDA-CFSAN 2001a). However, 11 of 151 imported and
4 of 115 domestic cantaloupe samples in the same surveys were positive for
Salmonella
or
Shigella
. These results appear consistent with the fact that multiple outbreaks
occurred in 1997, 2000, 2001, and 2002 due to
Salmonella
- contaminated cantaloupe
imported from Mexico (Table 1.1). A large survey of cantaloupe and environmental
samples from six farms and packing plants in South Texas and three farms in Mexico
resulted in 5/950 and 1/300 cantaloupes positive for
Salmonella
, respectively (Castillo
and others 2004). Irrigation-related samples of cantaloupe production (e.g., water
source, tank, in fi eld) revealed a higher incidence of
Salmonella
for both Texas and
Mexico farms: 13/140 (9.2%) and 10/45 (22.2%), respectively, compared to the com-
modity. Moreover, generic
E. coli
was isolated at signifi cant levels from some of the
samples of Texas and Mexico cantaloupe (3.9%, 25.7%) and Texas and Mexico irriga-
tion water (22.8% and 31.1%, respectively) (Castillo and others 2004). It is noteworthy
that none of the 150 fi eld and prewash cantaloupes from Mexico were positive for
E.
coli
, compared to 39/75 (52%) and 38/75 (51%) positive samples for the postwash
and packed cantaloupe, respectively. Although the concentrations of
Salmonella
and
generic
E. coli
in these samples were not reported, these results refl ect a prevalence
of fecal contamination of water sources (well, river, aquifer, canal, dam), suggesting
they may be sources of both pre- and postharvest contamination. Fecal contamination
of postharvest processing water is an obvious potential source of cross-contamination
of cantaloupes (Castillo and others 2004).
The fi tness characteristics of pathogens in the environment are important for their
long-term survival and exposure to produce. The long-term persistence in the environ-
ment of some foodborne pathogen strains is exemplifi ed by a strain of
S.
Enteritidis
implicated in at least one major outbreak, and possibly a minor outbreak, associated
with raw almonds in 2000/01 (Isaacs and others 2005) and 2005/06 (Ledet Muller and
others 2007), respectively. The
S.
Enteritidis outbreak strain, subtyped as phage type
30, was isolated from a suspect orchard at multiple times over at least a 5-year period,
>
