For the positive flies, the geometric mean carriage (log10
CFU/fly) was 2.93F1.24 for sugar–milk, 3.77F1.28 for steak, and 2.25F0.64 for the potato salad. In the second series of
experiments, the transfer of bacteria by individual flies from contaminated food to the inner surface of a sterile jar per each
landing was determined. E. coli transferred from the sugar–milk was 3.5F0.7 log10 CFU/fly-landing, 3.9F0.7 for steak and
2.61F1.16 for the potato salad. From the initial contamination levels of bacteria and the number of transferred bacteria, it can
be calculated that flies contaminate clean surfaces with approximately 0.1 mg of food per landing.