Combined effect of temperature, water activity and salt content on the growth and gene expression of Listeria monocytogenes in a dry-cured ham model system

Abstract

The combined effect of temperature, water activity (a_w) and NaCl content, usually found in dry-cured ham, on the growth and expression of the virulence and stress-related genes of Listeria monocytogenes was evaluated in a dry-cured ham model system. The highest growth of this pathogen was observed at 15 °C and, at 0.98 and 0.96 a_w values. At 0.94 and 0.92 a_w values, moderate NaCl levels stimulated the L. monocytogenes growth and repressed the expression of the four tested genes. At 7 °C, the expression of the plcA gene was favored while at 15 °C the hly and iap genes were activated. Preventive actions based on temperature, a_w and salt content should be taken to minimise risks associated with growth and gene expression of L. monocytogenes in dry-cured ham.

Keywords: Absolute quantification; Dry-cured ham; L. monocytogenes; Stress-response gene; Virulence genes.