In this task, you are given a sentence. You are expected to write the name of the organism substances in the body mentioned in the input. Although there might be several correct answers, you need to write one of them.

[EX Q]:  If a sample ' s results met any of these three criteria , then the sample was evaluated as a pathogen .
[EX A]: sample

[EX Q]:  The goal of this study was to determine whether immunosuppression plays a role in the level and duration of fecal shedding of Escherichia coli O157 .
[EX A]: fecal

[EX Q]:  A 20 - mul aliquot of the supernatant was added to 12 . 5 mul of assay buffer ( 20 mm ATP , 40 mm MgCl2 , 0 . 4 m Tris - Cl , pH 7 . 8 ) .
[EX A]:
supernatant