Agriculture Reference
In-Depth Information
1.0E+07
100000
1.0E+06
10000
1.0E+05
1000
1.0E+04
1.0E+03
H7
F4546
E. coli O157
NM 98A06026
Bredeney
3VIPHE
Muenchen
HERV2C
Salmonella
Figure 18.6.
The sensitivity of IMB-TRF method for detecting different strains of
E. coli
and
Salmonella
.
Counter that provided pulsed excitation and delayed emission measurements
(PerkinElmer Wallac, Turku, Finland).
Figure 18.6 shows the sensitivity of the IMB-TRF method for detecting different
strains of
E. coli
and
Salmonella
.
Bacterial samples with indicated concentrations were fi rst treated with proper
IMBs. The captured bacteria were then reacted with either Eu-labeled (for
E. coli
) or
Sm - labeled (for
Salmonella
) antibodies prior to TRF measurements (Tu and others
2002). As shown, detection limits were thus 750 CFU/ml for
E. coli
and 250 CFU/ml
for
Salmonella
. Similar trends were found with
Salmonella
strains Stanley HO558,
Anatum 4317, Infantis F4319, and Newport H1275 (data not shown).
To test the feasibility of using the developed IMB-TRF method to detect the patho-
gens in the alfalfa sprouts, experiments shown in Figure 18.7 were performed (Tu and
others 2003b). Commercially obtained alfalfa sprouts were inoculated with the patho-
gens at indicated levels and then “stomachered” and incubated for 4.5 h at 37 °C. Data
shown indicated that with crushed sprouts, the IMB-TRF could easily detect the pres-
ence of
E. coli
O157:H7 and
E. coli
O157:NM. However, the approach failed to detect
Salmonella
under the experimental conditions. The basis for this has yet to be deter-
mined but it has been reported by Castro-Rosas and Escartin (2000) that
Vibrio chol-
erae
O1 and
Salmonella typhi
showed no growth when inoculated onto alfalfa sprouts
24 h after germination. They attributed this observation to the abundance of competing
background microfl ora at 24 h into the germination process.
Detection of Pathogens in Laboratory-Cultivated Sprouts
Grown from Inoculated Seeds
Results of Figure 18.6 indicated that using whole alfalfa sprouts for pathogen detection
by IMB-TRF might have its drawbacks. Thus, we decided to germinate contaminated
