Agriculture Reference
In-Depth Information
used as an indicator of fecal contamination in food or environmental samples. Selective
cultural methods combined with molecular genotyping techniques can be used to track
the movement of the species in natural environments. We used this approach to deter-
mine sources of enteric bacteria in sweet cherry production systems and to examine
their fate during harvest. Tree fruit samples collected before harvest or after hydro-
cooling and cecal swabs from downed birds were analyzed for the presence of generic
E. coli
. Hand swabs were also obtained from pickers and workers on sorting lines.
Table 2.2 shows that
E. coli
was never recovered from fruit collected before
harvest, but 23.2% of an equal number of samples of harvested, hydro-cooled fruit
samples were positive.
Hydro-cooling water in all the test orchards was chlorinated and
E. coli
was never
found in water samples, although one operation employed an unchlorinated dump tank
from which
E. coli
was recovered. The bacterium was also present in 35.7% of swabs
performed on hands of pickers, and 15% from line sorters. Genotyping by the entero-
bacterial repetitive intergenic consensus (ERIC)-PCR reaction was used to establish
genetic relatedness among isolates from all the samples. As shown in Figure 2.2,
genotypes associated with birds were found on the hands of pickers and sorters and
in fi nished fruit.
This investigation confi rmed that wildlife is a signifi cant source of enteric bacteria
in sweet cherry production systems. The inability to isolate
E. coli
from preharvest
fruit suggests that fecal contamination is likely heterogeneously distributed in the
orchard environment. Harvest and postharvest handling lead to the dissemination of
enteric bacteria through harvested fruit, principally by contact with hands. Cherries
destined for the fresh market are always harvested manually to maintain desirable
quality attributes, notably the presence of an intact stem. The motion required to
remove intact fruit from the tree cannot be accomplished with a gloved hand, and
irritation or injuries to index fi ngers are frequent, as shown in Figure 2.3.
Hands quickly become heavily soiled, dry, and chapped over the course of
a typical harvest day. Work schedules preclude frequent stops for washing with soap
and water; and available options for hand disinfection in the fi eld, such as disposable
alcohol-based pads, are either impractical or ineffective. Although worker sanitation
has vastly improved in response to an increasing awareness of food safety issues,
there remains a need to develop practical solutions to hand disinfection under fi eld
conditions.
Table 2.2.
Proportions of pre- and postharvest fruit, bird, and hand samples positive for the
presence of
E. coli
in cherry orchards
Orchard
Fruit on
the Tree
Birds
Pickers '
Hands
Sorters '
Hands
Fruit from
Packing Line
Dump
Tank
1
0/30
15/30
3/10
1/10
0/10
NA
2
0/30
11/30
12/30
3/30
1/20
NA
3
0/5
NA
7/20
5/20
7/19
NA
4
0/5
NA
3/20
3/20
8/20
2/2
%
0
86.6
35.7
15.0
23.2
100
NA = no samples available.
