When portions of peptone water, milk or fluid from ground beef
stomached with diluent that contained E. coli at numbers of
6 log cfu ml1 were incubated at temperatures between of 52, 59,
66 or 72 C for between 0 and 80 min, 0 and 12 min, 0 and 90 s or
0 and 60 s, respectively, the numbers of viable cells were 2 log
units less than the initial numbers. With such heating treatments
the DNA extracted from samples treated with deoxycholate and
PMA generally gave Ct values somewhat higher than the values that
would be expected for the numbers of viable cells recovered
(Fig. 3). With longer heating times the numbers of viable cells were
>2 log units less than the initial numbers. Then the Ct values
obtained with DNA extracted from samples treated with deoxycholate
and PMA were generally similar irrespective of the number
of viable cells. Results with lower initial numbers of E. coli in the
peptone water, milk or stomacher fluid were comparable. For plots
of log numbers of viable cells against Ct values for DNA from
deoxycholate and PMA-treated samples from heated liquids in
which the numbers of viable cells were 2 log units less than the
initial numbers, the R2 values were 0.84 and the slopes were
between 2.06 and 2.49 Ct log cfu1
When portions of peptone water, milk or fluid from ground beef
stomached with diluent that contained E. coli at numbers of
6 log cfu ml1 were incubated at temperatures between of 52, 59,
66 or 72 C for between 0 and 80 min, 0 and 12 min, 0 and 90 s or
0 and 60 s, respectively, the numbers of viable cells were 2 log
units less than the initial numbers. With such heating treatments
the DNA extracted from samples treated with deoxycholate and
PMA generally gave Ct values somewhat higher than the values that
would be expected for the numbers of viable cells recovered
(Fig. 3). With longer heating times the numbers of viable cells were
>2 log units less than the initial numbers. Then the Ct values
obtained with DNA extracted from samples treated with deoxycholate
and PMA were generally similar irrespective of the number
of viable cells. Results with lower initial numbers of E. coli in the
peptone water, milk or stomacher fluid were comparable. For plots
of log numbers of viable cells against Ct values for DNA from
deoxycholate and PMA-treated samples from heated liquids in
which the numbers of viable cells were 2 log units less than the
initial numbers, the R2 values were 0.84 and the slopes were
between 2.06 and 2.49 Ct log cfu1
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