Browsing by Author "Wiedmann, Martin"

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    Implementing Targeted Good Manufacturing Practices and Sanitation Procedures to Minimize Listeria Contamination of Smoked Seafood Products
    Gall, Ken; Scott, Virginia N.; Collette, Robert; Jahncke, Michael L.; Hicks, Doris; Wiedmann, Martin (2004)
    The Smoked Seafood Working Group (SSWG), a collaboration of two national industry trade organizations, smoked seafood processors and academia, developed guidelines to minimize Listeria monocytogenes contamination of finished products in smoked seafood operations. The SSWG identified five elements required for a complete Listeria control program: (1) Listeria specific Good Manufacturing Practices (GMPs) and sanitation procedures, (2) employee training, (3) environmental microbiological monitoring and testing, (4) raw material controls, and (5) temperature controls for finished product. This manuscript describes specific GMPs and sanitation procedures to minimize Listeria contamination in smoked seafood operations. Targeted procedures that need to be implemented include GMPs to prevent cross contamination caused by improper design and layout of processing operations, the movement of people and equipment in the plant, and inadequate employee hygiene and food handling practices. In addition, cleaning and sanitation procedures for equipment and the processing plant environment that are designed to target Listeria contamination specifically need to be in place.
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    Salmonella enterica serovar Cerro displays a phylogenetic structure and genomic features consistent with virulence attenuation and adaptation to cattle
    Cohn, Alexa R.; Orsi, Renato H.; Carroll, Laura M.; Liao, Jingqiu; Wiedmann, Martin; Cheng, Rachel A. (Frontiers, 2022-11-30)
    Salmonella enterica subsp. enterica (S.) serovar Cerro is rarely isolated from human clinical cases of salmonellosis but represents the most common serovar isolated from cattle without clinical signs of illness in the United States. In this study, using a large, diverse set of 316 isolates, we utilized genomic methods to further elucidate the evolutionary history of S. Cerro and to identify genomic features associated with its apparent virulence attenuation in humans. Phylogenetic analyses showed that within this polyphyletic serovar, 98.4% of isolates (311/316) represent a monophyletic clade within section Typhi and the remaining 1.6% of isolates (5/316) form a monophyletic clade within subspecies enterica Clade A1. Of the section Typhi S. Cerro isolates, 93.2% of isolates (290/311) clustered into a large clonal clade comprised of predominantly sequence type (ST) 367 cattle and environmental isolates, while the remaining 6.8% of isolates (21/311), primarily from human clinical sources, clustered outside of this clonal clade. A tip-dated phylogeny of S. Cerro ST367 identified two major clades (I and II), one of which overwhelmingly consisted of cattle isolates that share a most recent common ancestor that existed circa 1975. Gene presence/absence and rarefaction curve analyses suggested that the pangenome of section Typhi S. Cerro is open, potentially reflecting the gain/loss of prophage; human isolates contained the most open pangenome, while cattle isolates had the least open pangenome. Hypothetically disrupted coding sequences (HDCs) displayed clade-specific losses of intact speC and sopA virulence genes within the large clonal S. Cerro clade, while loss of intact vgrG, araH, and vapC occurred in all section Typhi S. Cerro isolates. Further phenotypic analysis suggested that the presence of a premature stop codon in speC does not abolish ornithine decarboxylase activity in S. Cerro, likely due to the activity of the second ornithine decarboxylase encoded by speF, which remained intact in all isolates. Overall, our study identifies specific genomic features associated with S. Cerro’s infrequent isolation from humans and its apparent adaptation to cattle, which has broader implications for informing our understanding of the evolutionary events facilitating host adaptation in Salmonella.
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    Small Produce Farm Environments Can Harbor Diverse Listeria monocytogenes and Listeria spp. Populations
    Belias, Alexandra; Strawn, Laura K.; Wiedmann, Martin; Weller, Daniel (2021-01)
    A comprehensive understanding of foodborne pathogen diversity in preharvest environments is necessary to effectively track pathogens on farms and identify sources of produce contamination. As such, this study aimed to characterize Listeria diversity in wildlife feces and agricultural water collected from a New York state produce farm over a growing season. Water samples were collected from a pond (n = 80) and a stream (n = 52). Fecal samples (n = 77) were opportunistically collected from areas <5 m from the water sources; all samples were collected from a <0.5-km(2) area. Overall, 86 (41%) and 50 (24%) of 209 samples were positive for Listeria monocytogenes and Listeria spp. (excluding L. monocytogenes), respectively. For each positive sample, one L. monocytogenes or Listeria spp. isolate was speciated by sequencing the sigB gene, thereby allowing for additional characterization based on the sigB allelic type. The 86 L. monocytogenes and 50 Listeria spp. isolates represented 8 and 23 different allelic types, respectively. A subset of L. monocytogenes isolates (n = 44) from pond water and pond-adjacent feces (representing an similar to 5,000-m(2) area) were further characterized by pulsed-field gel electrophoresis (PFGE); these 44 isolates represented 22 PFGE types, which is indicative of considerable diversity at a small spatial scale. Ten PFGE types were isolated more than once, suggesting persistence or reintroduction of PFGE types in this area. Given the small spatial scale, the prevalence of L. monocytogenes and Listeria spp., as well as the considerable diversity among isolates, suggests traceback investigations may be challenging. For example, traceback of finished product or processing facility contamination with specific subtypes to preharvest sources may require collection of large sample sets and characterization of a considerable number of isolates. Our data also support the adage "absence of evidence does not equal evidence of absence" as applies to L. monocytogenes traceback efforts at the preharvest level. HIGHLIGHTS There is considerable Listeria diversity in the farm environment investigated. Listeria subtypes were reintroduced or persisted over the growing season. Four L. monocytogenes PFGE types were shared between feces and pond samples.
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    Treatment Options to Eliminate or Control Growth of Listeria monocytogenes on Raw Material and on Finished Product for the Smoked Fish Industry
    Jahncke, Michael L.; Collette, Robert; Hicks, Doris; Wiedmann, Martin; Scott, Virginia N.; Gall, Ken (2004)
    The Smoked Seafood Working Group (SSWG), a collaboration of the National Fisheries Institute, the National Food Processors Association, several smoked fish processors and universities, reviewed scientific papers that describe possible treatments to eliminate or reduce the amount of Listeria monocytogenes present on incoming raw material and eliminate or minimize its growth on finished product. Suggested treatment options that are approved for use on seafood, can be used by most commercial smoked fish companies, and have potential to significantly reduce L. monocytogenes numbers on incoming raw fish include (1) washing of raw fish with water containing chlorine and (2) treatment of raw fish with calcium hydroxide solution (pH 12). Other potential treatments approved for raw materials include washing of fish with acidified sodium chlorite solutions, ozone treatment, steam surface pasteurization, and electrochemical brine tank treatments. Treatment options to control L. monocytogenes on finished product include (1) freezing of finished product to stop growth; and (2) addition of approved chemical growth inhibitors. Other treatment options that have potential to eliminate L. monocytogenes or control its growth on finished product but that are not currently approved for use on seafood include addition of natural growth inhibitors, addition of high levels of Carnobacterium piscicola (~2 x 106 CFU/g), and irradiation. All treatment options require validation under commercial processing conditions.
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    Whole-Genome Sequencing-Based Characterization of Listeria Isolates from Produce Packinghouses and Fresh-Cut Facilities Suggests Both Persistence and Reintroduction of Fully Virulent L. monocytogenes
    Sullivan, Genevieve; Orsi, Renato H.; Estrada, Erika; Strawn, Laura K.; Wiedmann, Martin (American Society for Microbiology, 2022-11-01)
    The contamination of ready-to-eat produce with Listeria monocytogenes (LM) can often be traced back to environmental sources in processing facilities and packinghouses. To provide an improved understanding of Listeria sources and transmission in produce operations, we performed whole-genome sequencing (WGS) of LM (n = 169) and other Listeria spp. (n = 107) obtained from 13 produce packinghouses and three fresh-cut produce facilities. Overall, a low proportion of LM isolates (9/169) had inlA premature stop codons, and a large proportion (83/169) had either or both of the LIPI-3 or LIPI-4 operons, which have been associated with hypervirulence. The further analysis of the WGS data by operation showed a reisolation (at least 2 months apart) of highly related isolates (,10 hqSNP differences) in 7/16 operations. Two operations had highly related strains reisolated from samples that were collected at least 1 year apart. The identification of isolates collected during preproduction (i.e., following sanitation but before the start of production) that were highly related to isolates collected during production (i.e., after people or products have entered and begun moving through the operation) provided evidence that some strains were able to survive standard sanitation practices. The identification of closely related isolates (,20 hqSNPs differences) in different operations suggests that cross-contamination between facilities or introductions from common suppliers may also contribute to Listeria transmission. Overall, our data suggest that the majority of LM isolates collected from produce operations are fully virulent and that both persistence and reintroduction may lead to the repeat isolation of closely related Listeria in produce operations. IMPORTANCE Listeria monocytogenes is of particular concern to the produce industry due to its frequent presence in natural environments as well as its ability to survive in packinghouses and fresh-cut processing facilities over time. The use of whole-genome sequencing, which provides high discriminatory power for the characterization of Listeria isolates, along with detailed source data (isolation date and sample location) shows that the presence of Listeria in produce operations appears to be due to random and continued reintroduction as well as to the persistence of highly related strains in both packinghouses and fresh-cut facilities. These findings indicate the importance of using high-resolution characterization approaches for root cause analyses of Listeria contamination issues. In cases of repeat isolation of closely related Listeria in a given facility, both persistence and reintroduction need to be considered as possible root causes.