Comparison of Listeria monocytogenes Invasion among the Serotypes Isolated from Foods and Human

Introduction: Listeria monocytogenes is generally isolated from food, especially meat products, and 90% of the isolates are 1/2a, 1/2b and 4b. The pathogen causes foodborne disease by invasion intestinal tissue, and thus, they may have different invasion efficiencies among serotypes.

Purpose: The objective of this study was to evaluate the invasion efficiency of L. monocytogenes among serotypes, and between food isolates and human isolates.

Methods: To compare the invasion efficiency, L. monocytogenes serotypes (1/2a, 1/2b, 1/2c, 3b, 4b, 4d) isolated from foods (14 strains) and human (11 strains) were used. L. monocytogenes inocula were prepared in minimum essential medium (MEM) supplemented with 20% fetal bovine serum to obtain multiplicity of infection of 100. Monolayer (5×10⁴ cells/ml) of Caco-2 cell grown in 24-well tissue culture plates was washed twice with phosphate buffered solution. One milliliter of the inocula were inoculated into the cell monolayer of Caco-2 cells, and they were incubated in 5% CO₂ at 37°C for 2 h. After treating Caco-2 cells with 50 μg/ml gentamicin and 0.5%Triton X-100, resulting suspensions were plated on tryptic soy agar with 0.6% yeast extract to enumerate infected L. monocytogenes.

Results: The invasion efficiencies of L. monocytogenes strains into Caco-2 cell were dependent on serotypes. However, the invasion efficiencies of L. monocytogenes food isolates were similar to those of L. monocytogenes human isolates.

Significance: This result indicates that different serotypes of L. monocytogenes may have different invasion efficiencies into Caco-2 cell.