Agriculture Reference
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1.0E+06
1.0E+05
1
10
100
1.0E+04
1.0E+03
H7
E. coli O157:H7
NM
Bredeney
Salmonella
Muenchen
CFU/mL
Figure 18.7. Detection of pathogens on crushed sprouts.
alfalfa seeds (4 CFU/g) in our laboratory using sterile Mason jars and sterile tap water
for irrigation. Thus, an analysis of spent irrigation water should indicate whether the
sprouts, and therefore the seeds, are contaminated by pathogens. Experimentally,
alfalfa seeds artifi cially contaminated with E. coli O157 or Salmonella were used to
produce sprouts (Tu and others 2002). As shown in Figure 18.8, water sample analyses
were applicable for the detection of both E. coli O157 and Salmonella .
Detection of Pathogens in Irrigation Water and Sprouts
Although spent irrigation water testing is recommended by the FDA (1999), it may
give false negative results because microbial counts in the irrigation water are, on the
average, 1 log lower than those detected in sprout samples (FDA 1999; Fu and others
2001). For this reason, we chose to apply the developed detection method to both the
water and sprouts simultaneously. We did not utilize the Seward Stomacher for pum-
meling sprouts germinated from lab-inoculated seeds because of complications
described in Figure 18.6. Instead, whole sprouts were aseptically transferred to the
proper culture medium for the enrichment. With this experimental design, both the
sprouts and the spent irrigation water equally showed the presence of the pathogens
as depicted in Figure 18.9. Unlike the results described in Figure 18.7, the use of
sprouts germinated from contaminated seeds, under applied laboratory conditions,
showed positive detection for both E. coli O157 and Salmonella . Apparently, the
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