Abstract
Dry-cured ham can be contaminated with Listeria monocytogenes during its industrial processing. The use of bacteriocins could ensure the safety of such meat products, but their effect on pathogen physiology is unknown. Therefore, the impact of enterocins A and B on the L. monocytogenes population, and the expression patterns of five genes (inlA, inlB, clpC, fbpA and prfA) related to adhesion/invasion and virulence regulation have been monitored in sliced dry-cured ham during 30 d of storage in refrigeration (4 °C) and temperature-abuse conditions (20 °C). L. monocytogenes strains S2 (serotype 1/2a) and S7-2 (serotype 4b) counts were reduced by 0.5 and 0.6 log units immediately after the application of enterocins A and B, a decrease lower than previously reported. Differences in gene expression were found between the two strains. For strain S2, expression tended to increase for almost all genes up to day seven of storage, whereas this increase was observed immediately after application for strain S7-2; however, overall gene expression was repressed from day one onwards, mainly under temperature-abuse conditions. L. monocytogenes strains investigated in the present work exhibited a mild sensitivity to enterocins A and B in sliced dry-cured ham. Bacteriocins caused changes in the expression patterns of virulence genes associated with adhesion and invasion, although the potential virulence of surviving cells was not enhanced.
Highlights
Listeria monocytogenes is a food-borne pathogenic bacteria, which causes a serious disease called listeriosis with one of the highest hospitalization rates in developed countries, affecting mainly susceptible groups such as new-born infants, children, pregnant women, elderly and immunocompromised individuals [1]
The purpose of this work was to evaluate the effect of an extract of enterocins A and B produced by E. faecium INIA TAB7 on the viability and the relative expression of genes involved in the virulence of two strains of L. monocytogenes in sliced dry-cured ham, stored under a strict refrigeration temperature (4 ◦ C) and temperature-abuse conditions (20 ◦ C) for 30 days
This paper provides additional information on L. monocytogenes virulence and invasiveness potential in a real food matrix
Summary
Listeria monocytogenes is a food-borne pathogenic bacteria, which causes a serious disease called listeriosis with one of the highest hospitalization rates in developed countries (more than 90% of cases), affecting mainly susceptible groups such as new-born infants, children, pregnant women, elderly and immunocompromised individuals [1]. Contaminated food is the major source of infection, and the gastrointestinal tract is the primary site of entry for the pathogen [2]. PrfA, considered the major virulence factor of L. monocytogenes, positively regulates the transcription of several virulence genes, including inlA and inlB [6]. Fish and dairy products are commonly associated with human infections, foods of plant origin or frozen foods have been involved [7]. Dry-cured ham is an RTE meat product considered safe due to its reduced water activity (aw ) and high salt content [8,9], but can be contaminated with L. monocytogenes during post-processing [10,11]
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