A single strain culture of Lm320 (ATCC 19115, serotype 4b) was
used in studies on lettuce, and Lm376, an environmental strain
obtained from a Scottish smoked salmon facility, was used in the
studies at the same smoked salmon production facility. To test the
efficacy of ListShield™ when challenged with a cocktail of bacteria,
a 1:1:1 mixture of three L. monocytogenes strains, Lm68 (serotype 1/
2b), Lm82 (serotype 1/2a) and Lm320 (ATCC 19115, serotype 4b)
was used in the apple, cheese, smoked salmon, and frozen entrees
studies. The strains were grown in LB media at 37 ± 2 C for up to
24 h to a target concentration of ca. 108 colony forming units (CFU)/
mL. Challenge cultures were diluted in LB for each experiment as
necessary to achieve a specific contaminating dose specified in the
respective sections below and unless otherwise stated, the volume
of bacteria added was between 0.5 mL and 1 mL.