The spread plate enumeration technique was used for all experiments except as indicated. Populations of L. monocytogeneswere
recovered on modified Oxford agar (MOX) (Becton Dickinson and
Co.) with 48-h incubation at 37
◦
C. MacConkey sorbitol agar (Becton Dickinson and Co.) supplemented with cefixime-tellurite (Dynal
Biotect A.S.A, Oslo, Norway) (CT-SMAC) was used as a selective media forE. coliO157:H7 and plates were incubated at 37◦
C for 24 h
before colonies were counted. The number of mesophilic aerobic
bacteria was determined by plating on PCA, and incubated at 37
◦
C for 48 h. Dichloran Rose Bengal Chloramphenicol agar (DRBC)
(EMD Chemicals Inc.) was used to enumerate yeasts and molds. The
DRBC agar plates were incubated in the dark at 25◦
C for 5 d before
yeast and mold colonies were counted. For confirming the absence
of any microorganisms on laboratory distilled water, preliminary experiments were done by plating water sample on all types of media
as described previously.