Processing-Dependent and Clonal Contamination Patterns of Listeria monocytogenes in the Cured Ham Food Chain Revealed by Genetic Analysis

Abstract

The quantitative and qualitative patterns of environmental contamination by Listeria monocytogenes were investigated in the production chain of dry-cured Parma ham. Standard arrays of surfaces were sampled in processing facilities during a single visit per plant in the three compartments of the food chain, i.e., ham production (19 plants) and postproduction, which was divided into deboning (43 plants) and slicing (25 plants) steps. The numbers of sampled surfaces were 384 in ham production, with 25 positive for L. monocytogenes, and 1,084 in postproduction, with 83 positives. Statistical analysis of the prevalence of contaminated surfaces showed that in ham production, contamination was higher at the beginning of processing and declined significantly toward the end, while in postproduction, prevalence rose toward the end of processing. Prevalence was higher in the deboning facilities than in slicing facilities and was dependent on the type of surface (floor/drainage > clothing > equipment). The qualitative pattern of contamination was investigated through an analysis of the survey isolates and a set of isolates derived from routine monitoring, including longitudinal isolations. Pulsed-field gel electrophoresis (PFGE) and whole-genome singlenucleotide polymorphism (SNP) analysis revealed a remarkable clonality of L. monocytogenes within plants, with the detection of 16 plant-specific clones out of 17 establishments with multiple isolates. Repeated detections of clonal isolates >6 months apart were also observed. Six was the maximum number of between-isolate differences in core SNPs observed within these clones. Based on the same six-SNP threshold, three clusters of clonal isolates, shared by six establishments, were also identified. The spread of L. monocytogenes within and between plants, as indicated by its clonal behavior, is a matter of concern for the hygienic management of establishments.

Genome‐wide‐analyses of Listeria monocytogenes from food‐processing plants reveal clonal diversity and date the emergence of persisting sequence types

“…L. monocytogenes is divided into four Lineages, of which lineage I isolates are often associated with human outbreaks, whereas Lineage II isolates are often associated with food and food processing environments (Valderrama and Cutter, ; Maury et al ., ). Sequence type (ST) 121 (ST121) identified by Multi Locus Sequence Typing (MLST) is a persistent ST, and has been found in fish processing plants (Wulff et al ., ), meat processing plants (Martin et al ., ; Morganti et al ., ) and in many other food processing plants (Hein et al ., ; Chiara et al ., ; Ciolacu et al ., ; Schmitz‐Esser et al ., ). ST121 is the most common ST isolated from food samples; however, it is rarely isolated from infected patients (Althaus et al ., ; Ebner et al ., ; Maury et al ., ).…”

Closing gaps for performing a risk assessment on Listeria monocytogenes in ready‐to‐eat (RTE) foods: activity 3, the comparison of isolates from different compartments along the food chain, and from humans using whole genome sequencing (WGS) analysis

“…monocytogenes can remain on equipment or surfaces (Mettler and Carpentier, 1999) for several months or years (Jessen and Lammert, 2003;Carpentier and Cerf, 2011). WGS has recently been shown to be an invaluable tool to detect persistent strains in processing plants (Fagerlund et al, 2016;Morganti et al, 2016). What is of concern is that the presence of persistent cells on food-www.efsa.europa.eu/publications 97 EFSA Supporting publication 2017:EN-1151…”

Design Elements of Listeria Environmental Monitoring Programs in Food Processing Facilities: A Scoping Review of Research and Guidance Materials

“…For example, WGS has already been used in food safety laboratories to understand Lm biology, evolution and virulence (Bergholz, Switt, & Wiedmann, ; Orsi & Wiedmann, ; Orsi, Bakker, & Wiedmann, ), and persistence and transmission in food production environments (Stasiewicz, Oliver, Wiedmann, & Bakker, ). From the studies included in this scoping review, WGS was only employed in 1 EM study to trace Lm in a cured ham food chain (Morganti et al., ) and in another to investigate persistent and disinfectant‐resistant Lm in a newly built RTE pork processing plant (Ortiz et al., ). Subtyping and advanced molecular methods present a valuable tool for improving Lm surveillance efforts and may soon find more widespread adoption by food processing facilities in routine EM programs for improving detection and elimination of Listeria contamination.…”