Bacterial strain and culture conditions The organism that was used in this study is L. monocytogenes, strain Scott A, serotype 4b (USFDA). Stock cultures were maintained frozen at −70 ◦C in brain heart infusion broth (BHI; TEKnova, Hollister, Calif., U.S.A.) with 20% glycerol. Working cultures were prepared by inoculating a loopful of the stock culture
into BHI and incubating for 18 to 24 h at 37 ◦C.