Behaviour of cold-adapted Listeria monocytogenes under conditions representative of meat processing plants

Abstract

The objective of this study was to examine filamentation characteristics of cold-adapted Listeria monocytogenes under conditions representative of a meat processing plant. Initial analysis of 16 strains found three strains with a wide range of filamentation characteristics and these were used in subsequent experiments. L. monocytogenes were grown at 3°C in Tryptic Soy Broth (TSB), TSB with 4% or 8% NaCl, TSB adjusted to pH 5.5, 6 or 8.5, and TSB with 4% NaCl adjusted to pH 6. Filamentation characteristics were determined with microscopy and flow cytometry. Filamentation in saline conditions peaked early in the logarithmic phase whereas in acidic conditions filamentation increased steadily over time. In alkaline media filamentation peaked twice during the growth cycle. A combination of acidic and saline conditions resulted in an initial peak, followed by gradual increase of filamentation over time. The length of filaments increased with an increase in stressful conditions.