2. Materials and methods
2.1. Strain
Food samples, including different kind of cheeses and vegetables,
were purchased from local food stores (Columbus, OH) and
were screened for isolates with antimicrobial activity. The
screening procedure of He et al. (2007) was used with modifications.
Briefly, samples were suspended in 0.1% peptone water and
homogenized by a stomacher or a blender. The homogenates were
serially diluted and passed through hydrophobic grid membranes
with pore size of 0.45 mm (ISO-GRID; Neogen Corporation, Lansing,
MI). The membranes were then placed onto tryptose agar and
incubated at 30 _C for 48 h. The membranes carrying bacterial
colonies were removed and saved, but the agar plates were overlaid
with soft agar seeded with Listeria innocua ATCC 33090 or Escherichia
coli K-12. The seeded agar plates were incubated at 37 _C
overnight and inspected for signs of antimicrobial activity. Colonies
on the membrane that produced inhibitory zones were transferred
and streaked onto new tryptose agar plates. A sample of “Facai”, a
Chinese delicacy food (Gao, 1998), yielded a strain with potent
antimicrobial activity against L. innocua and was given OSY-7LA
designation.