The mixtures were vortexed
at maximum speed for 1 min. After vortexing, undiluted suspensions
(0.1ml in duplicate) and suspensions (0.1 ml in duplicate) serially diluted
in 0.1% PWwere surface-plated on tryptic soy agar (TSA; BBL/Difco)
and incubated at 37 °C for 24 h before E. coli O157:H7 colonies were
counted. The detection limit for the direct plating was 1.5 log CFU/coupon
(30 CFU/coupon).