To determine the limits of sample composite sizes on detecting low levels of E.coli O157:H7 in new, rapid 8 hr test kit formats. The effect of increased enrichment incubation times was evaluated to compensate for loss of detection sensitivity in larger composite sample sizes.
This study showed that the ability to detect low levels of E. coli O157:H7 in raw ground beef and raw beef trim composite samples using four 8 hr test kits varied with the product type being composited, the test kit, and the incubation time. There was no statistical difference between ABAX, Reveal, and RapidChek in detecting overall numbers of inoculated ground beef or trim samples (p>0.05). VIP detected significantly fewer positive samples than the other three methods for both ground beef and trim (p<0.05). The reason for this lower detection by VIP was not part of this study, but should be further investigated before compositing scheme recommendations can be made.
The study provided valuable insight on E. coli O157:H7 testing programs for beef processors, including recommendations on sampling composite sizes and incubation times.