title: 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 single-nucleotide 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.
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia-Romagna (IZSLER), Sezione di Parma, Parma, Italy.
authors.forename: Marina
authors.initials: M
authors.lastname: Morganti
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia-Romagna (IZSLER), Sezione di Parma, Parma, Italy.
authors.forename: Erika
authors.initials: E
authors.lastname: Scaltriti
authors.affiliation: Official Veterinary Service, Local Health Unit of Parma (AUSL), Parma, Italy Department of Public Health, Local Health Unit of Parma (AUSL), Parma, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Cozzolino
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia-Romagna (IZSLER), Sezione di Parma, Parma, Italy Direzione Sanitaria, Servizio di Analisi del Rischio, Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia-Romagna (IZSLER), Parma, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Bolzoni
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia-Romagna (IZSLER), Sezione di Parma, Parma, Italy.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Casadei
authors.affiliation: Official Veterinary Service, Local Health Unit of Parma (AUSL), Parma, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Pierantoni
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia-Romagna (IZSLER), Sezione di Parma, Parma, Italy.
authors.forename: Emanuela
authors.initials: E
authors.lastname: Foni
authors.affiliation: Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia-Romagna (IZSLER), Sezione di Parma, Parma, Italy Direzione Sanitaria, Servizio di Analisi del Rischio, Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia-Romagna (IZSLER), Parma, Italy stefano.pongolini@izsler.it.
authors.forename: Stefano
authors.identifier: http://orcid.org/0000-0002-4823-3562
authors.initials: S
authors.lastname: Pongolini
mesh_terms: D016521:Electrophoresis, Gel, Pulsed-Field; D004866:Equipment Contamination; D020387:Food Chain; D005511:Food Handling / Q000295:instrumentation / Q000379:methods; D005516:Food Microbiology; D005525:Food-Processing Industry / Q000295:instrumentation / Q000592:standards*; D008089:Listeria monocytogenes / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification*; D008088:Listeriosis / Q000382:microbiology / Q000517:prevention & control / Q000635:transmission; D020641:Polymorphism, Single Nucleotide; D000069466:Red Meat / Q000382:microbiology*