VARIATIONS IN THE SURVIVAL OF LISTERIA MONOCYTOGENES TO GROW IN BILE FROM PORCINE GALLBLADDERS

Abstract Text:

Listeria monocytogenes is a facultative intracellular, Gram-positive bacterium that can cause disease, including abortion, in sheep, goats, cattle, pigs and poultry. These animals are also known reservoirs for this pathogen and it is primarily acquired through ingestion of contaminated silage or soil. This bacterium’s ability to survive within the gastrointestinal tract and cross the intestinal lining is directly related to the ability of the pathogen to cause disease. However, it is not clear whether there are variations in the ability of this pathogen to survive. The purpose of this study was to determine whether variations exist in the ability of different serotypes of L. monocytogenes to survive within porcine gallbladder bile and if survival affected the ability of these bacteria to invade epithelial cells in vitro. Avirulent strain HCC23 (serotype 4a) and virulent strain 10403S (serotype 1/2a) were cultured in brain-heart-infusion (BHI) broth media to mid-logarithmic (OD₆₀₀= 0.5), then transferred to bile collected from pigs 30 d of age (6.7 ± 0.1 kg BW). Anaerobic growth was monitered by viable plate counts on BHI agar. The influence of bile on invasion potential of L. monocytogenes was tested in colon epithelial cells (GPC-16) cultured in Eagle’s Minimal Essential Media with 20% fetal bovine serum. Cell culture media was supplemented with 10% bile and HCC23 or 10403S were inoculated at a multiplicity of infection of 100:1. Cultures were incubated at 37°C, 5% CO2. At 1 h and 2 h post infection, cells were washed to remove extracellular bacteria then lysed to release intracellular bacteria. Lysates were serially diluted and plated onto BHI agar. Survival of HCC23 in bile did not change (P = 0.3), though a decrease (P = 0.05) in survival of 10403S was observed 24 h after bile exposure. Virulent strain 10403S also had a decrease (P = 0.05) in invasion potential in the presence of bile. In contrast, avirulent strain HCC23 did not decrease (P = 0.08) in invasion potential in the presence of bile. Together with previous reports of variations in the intracellular presence of L. monocytogenes in the gallbladder, these results suggest that avirulent and virulent strains respond differently to the gastrointestinal environment and this difference may influence the outcome of the infectious process.

Keywords:

Listeria monocytogenes, pig, gallbladders