2.2.5. Enumeration of Salmonella and E. coli O157:H7
Fifty microliter aliquots of each of the samples were spiral-plated
onto two Tryptic Soy Agar (TSA) plates containing 100 μg/mL nalidixic
acid (TSAN) and two xylose lysine tergitol-4 (XLT-4) plates for Salmonella,
as well as two TSA plates containing 100 μg/mL rifampicin (TSAR) and
two Sorbitol MacConkey Agar (SMAC) plates for E. coli O157:H7. Plates
were incubated at 37 °C for 24 h before colonies were counted. Injured
cells were estimated by comparing the difference in cell populations
between non-selective and selective media (Wu, 2008; Gurtler et al.,
2010) as follows:
Injured cellsð Þ¼ % P