IAFP 2009 Program Book and Abstract Book - AB82

Significance: Strain H7550 and its cadmium sensitive derivative H7550cds are equally virulent for mice, and are both resistant to synthetic gastric fluid, but they may exhibit minor differences in the ability to form biofilms in vitro. LLO is required for virulence of this strain, as for other L. monocytogenes, but was not required for biofilm formation. Transposon mutant strain J22F was also avirulent for mice, providing the first evidence that adenylosuccinate lyase activity is required for virulence in mice. Further studies are needed to assess the possible role of pLM80 in fitness of the bacteria associated with the 1998 to 1999 outbreak. P1-56 Genotyping of Listeria monocytogenes Isolated from the Environment and Food Products in a Convenience Food Processing Plant SIMONA BLATTER, Roger Stephan and Claudio Zweifel University of Zurich, Institute for Food Safety and Hygiene, Vetsuisse Faculty, Zurich, Switzerland Introduction: L. monocytogenes as a foodborne pathogen has significant public health and economic impacts. The infection of humans may result in severe clinical disease as well as high mortality. Furthermore, L. monocytogenes contamination is one of the leading causes of recalls in processed foods. Among other foods, Ready-to-Eat products have been implicated as routes for human infection. Purpose: The aim was to investigate the occurrence and genetic diversity of L. monocytogenes strains from a convenience food-processing plant. Methods: Samples were obtained twice a week from the processing room, from machines and equipment of five sandwich production lines, and from products. Isolation of Listeria was accomplished by culture after enrichment (HalfFraser/Fraser broth and Palcam agar). For identification of L. monocytogenes, suspicious colonies were streaked onto Ottaviani Agosti agar. Genetic lineages were determined using the ASO-PCR multiplex system targeting the prfA virulence gene cluster. Moreover, strains were genotyped by REP-PCR to establish genetic relationships. Results: Of the 500 samples, 6.0% were positive for L. monocytogenes. Nearly half the positive samples (46.7%) originated from three slicers. Besides, five sandwiches (twice tuna; once each salmon, egg, and ham) tested positive, and L. monocytogenes were also isolated from tables, gloves, the floor, a conveyor belt, a spattle, a squeegee, and a water hose. Of the 30 isolated strains, 28 (93.3%) grouped into genetic lineage II, whereas two strains from the water hose belonged to lineage I. REP-PCR grouped the 30 strains into three different genotypes. Twenty-five (83.3%) strains belonged to only one genotype. On two slicers and a table, L. monocytogenes belonging to the dominating genotype were isolated in repeated samplings. Significance: Genotyping results indicate the predominance and persistence of a certain L. monocytogenes strain in the processing area of this convenience food-processing plant, even after cleaning and disinfecting procedures. Thus the slicing equipment, which is used for different products and also at different production lines, presents a possible source and risk factor for product contamination with L. monocytogenes. P1-57 Survival of Desiccated Listeria monocytogenes on Stainless Steel and Transfer to Salmon Products LISBETH TRUELSTRUP HANSEN, Lone Gram and Birte Fonnesbech Vogel Dalhousie University, Process Engineering and Applied Science, Halifax, NS, Canada Introduction: Listeria monocytogenes is a Gram-positive foodborne bacterial pathogen capable of colonizing food processing equipment and cross-contaminating processed foods, potentially causing foodborne listeriosis. A recent example is the 2008 Canadian outbreak from cross-contaminated meat products. The persisting capacity of L. monocytogenes is not fully explained. Food processing environments experience constant changes in relative humidity (RH), and contaminating microorganisms may be subjected to low RH conditions for extended periods of time. Purpose: The objective of this study was to examine the survival on stainless steel and subsequent transfer to salmon products of desiccated L. monocytogenes N53-1, a persistent food strain. Methods: During desiccation on stainless steel coupons at 43% RH and 15°C, survivors were enumerated by spread plating on BHI and Oxford agar. The physiological state of desiccated cells was observed by use of fluorescence microscopy with the LIVE/DEAD stain. Results: The survival of cells (initial count 7.7 log CFU/cm2) desiccated for 23 days in presence of 5% (w/v) NaCl was significantly (P < 0.05) higher (6.8 log CFU/cm2) than the survival of cells desiccated with 0.5% (w/v) NaCl (5.4 log CFU/ cm2). LIVE/DEAD fluorescence staining showed dominance of healthy (green) cells in 5% NaCl samples while damaged/ dead (red) cells dominated 0.5% NaCl samples. Allowing Listeria to form biofilm (2 d at 100% RH and 15°C) prior to desiccation improved the survival of 0.5% NaCl samples significantly, indicating the protective effect of the biofilm matrix. Also, cells pre-cultured in 5% NaCl before the biofilm/desiccation treatment survived significantly (P < 0.05) better than cells pre-cultured in 0.5% NaCl. The desiccated bacteria transferred easily from steel to smoked and fresh salmon, and transfer was proportional to the numbers of live cells on the steel coupons. Significance: In conclusion, we have shown that L. monocytogenes survived desiccation well, that the presence of salt during preculture and desiccation increased survival and that this in turn enhanced the transfer of bacteria to foods. P1-58 Growth of Listeria monocytogenes in Thawed Frozen Foods AI KATAOKA, Hua Wang and Philip H. Elliott Grocery Manufacturers Association, Science Operations, Washington, D.C., USA Introduction: FDA released a draft Compliance Policy Guide (CPG) on Listeria monocytogenes and draft guidance to industry in February 2008. FDA has proposed that Ready-to-Eat foods that do not support the growth of L. monocytogenes may contain up to 100 CFU/g. Frozen foods fall in that category, but once they are thawed, held refrigerated and consumed without further cooking, growth of Listeria may present a health hazard. 82 — Abstract Book Poster

IAFP 2009 Program Book and Abstract Book

Table of Contents for the Digital Edition of IAFP 2009 Program Book and Abstract Book