3.2. UV-C sensitivity of attenuated E. coli O1 57:H7 and S. Typhimurium
Showing a similar response to treatment as that of pathogenic
E. coli O157:H7, Shiga toxin-negative E. coli O157:H7 was inactivated
by 0.6 and 1.1 logs/fruit (on TSA media) after UV-C treatments at
doses of 15 and 74 mJ/cm2
, respectively (Fig. 2). Increasing doses
from 74 to 442 mJ/cm2 only produced an additional 0.3–0.4 log reduction
of the bacterium, and the injured cells in UV-C-treated samples represented
less than 8% of total cell population.
The population of attenuated S. Typhimurium decreased as UV dose
increased from 0 to 74 mJ/cm2 (0 to 10 s) (Fig. 2). Further increases in
UV doses did not increase the reduction of S. Typhimurium. The population
of Salmonella, when assessed on XLT-4 agar, was reduced by 0.4 and
1.3 log/fruit after 15 to 74 mJ/cm2 UV-C treatment. Similar reductions
(0.4 and 1.1 logs) were achieved when assessed on TSA. The cells injured
by UV-C represented a small percentage (≤10%) of total population
of Salmonella.