IAFP 2009 Program Book and Abstract Book - AB78

Purpose: The objective of this study was to examine the growth and survival behavior of L. innocua and E. coli cells after various exposures to Pulsed Light treatment. Methods: L. innocua (environmental isolate) and E. coli ATCC 25922) were grown to stationary phase in Tryptic Soy Broth (TSB) and diluted 10-fold in Butterfield’s Phosphate Buffer. One ml volumes were exposed to Pulsed Light doses (fluence) of up to 13.3 J/cm2 for both organisms. Surviving isolates from 1.1 and 10.1 J/cm2 were recovered and repeatedly exposed to additional Pulsed Light treatments. Untreated, single, and double Pulse Light exposed isolate survival curves and 24 h growth curves were generated and statistical differences were determined using two-way ANOVA. Results: Growth curves of L. innocua and E. coli isolates that were not exposed to Pulsed Light were not significantly different from growth curves of isolates exposed to 1.1 or 10.1 J/cm2 or isolates from a subsequent (second) exposure to Pulsed Light. The Pulsed Light inactivation curves for both unexposed organisms and isolates recovered from single or repeated exposure to Pulsed Light were not significantly different. Initial reductions after treatment with 1.1 J/cm2 ranged from 2.6 to 3.8 log CFU/ml while a reduction of from 5.0 to 5.8 was reached after exposure to 13.3 J/cm2. Significance: The results of this study show that Pulsed Light treatments can significantly reduce L. innocua or E. coli in clear liquids. The surviving cells did not exhibit changes in resistance or growth kinetics, which is important for practical applications of this technology. P1-46 PFGE as a Predictor of Listeria monocytogenes Biofilm Formation GORDON R. DAVIDSON, Annemarie L. Buchholz, Zhinong Yan and Elliot T. Ryser Michigan State University, Food Science and Human Nutrition, East Lansing, MI, USA Introduction: Persistence and spread of Listeria monocytogenes in food manufacturing and retail environments is greatly aided by the ability of this pathogen to form biofilms. While numerous Listeria isolates from environmental surveys have been serotyped and subjected to various strain-specific molecular typing methods, relatively few studies have characterized such strains in terms of biofilm formation, which could lead to improved Listeria intervention strategies. Purpose: In this study, the relationship between biofilm formation, serotype and pulsed-field gel electrophoresis (PFGE) type was determined in a set of 30 L. monocytogenes environmental isolates from one delicatessen. Methods: All 30 L. monocytogenes delicatessen isolates were serotyped using a PCR-based method with five different primer sets and then subjected to PFGE typing using the PulseNet protocol with restriction enzymes AscI and ApaI. Biofilm formation was quantified using a standard microtiter plate assay with Modified Welshimer’s Broth as the growth medium. After averaging the 9 optical density readings from triplicate wells for each of three replicates, each isolate was classified as a weak, medium or strong biofilm former. Results: Overall, 16, 7, 6 and 1 L. monocytogenes isolates belonged to serotypes 1/2b(3b), 1/2a(3a), 4b(d,e) and 4a/c, respectively. A total of 12 PFGE types grouped into three distinct clusters. All 7 strong biofilm-forming strains belonged to serotype 1/2a(3a) and to two closely related PFGE types containing a unique high kbp doublet using ApaI that were only 60.9% similar compared to the remaining 23 isolates. These 7 strong biofilm formers were isolated from multiple locations over 9 months. However, 4 weak and 2 medium biofilm-forming strains also persisted for 10 months, thereby weakening previous correlations between biofilm formation and persistence. Significance: These findings demonstrate that PFGE typing can be a predictor of L. monocytogenes biofilm formation. However, other factors in addition to biofilm formation are also clearly important in persistence. P1-47 Effect of Various Factors on the Formation of Biofilms by Four Strains of Listeria monocytogenes WLADIR B. VALDERRAMA and Catherine N. Cutter Pennsylvania State University, Food Science, University Park, PA, USA Introduction: It has been suggested that biofilm formation may be influenced by environmental factors. However, little information addresses the effect of multiple factors on biofilm formation by different strains of L. monocytogenes. Purpose: The purpose of this study is to investigate the ability of four different outbreak-related strains of L. monocytogenes to form biofilms as a function of pH, temperature, water activity, inoculum size, and nutrition level. Methods: Four L. monocytogenes isolates (FSLJ1-129, FSLR2-499, FSLJ1-003, FSLJ2-685) were screened for biofilm formation, using the microtiter plate method. Growth conditions were fixed for pH (5, 7, 9), water activity (0.92, 0.96, 0.98), nutrition level (0.25, 0.5, 0.75% of Tryptic Soy Broth), inoculum size (2, 4, 6 log CFU/mL), and three incubation temperatures (4, 22, 40°C). Biofilms were evaluated after 48 h of growth, and treated with crystal violet, after which optical density was measured at 595 nm. Data were analyzed by performing an analysis of variance in a full factorial design. Results: Factors (pH, temperature, water activity and inoculum size) and strain significantly affected biofilm formation (P 0.05) among the evaluated strains. Interactions between several factors were significant (P < 0.05) for biofilm formation. Additionally, morphological changes in biofilms were observed when combinations of factors were evaluated. Significance: These data are the first to demonstrate that multiple factors differentially influence biofilm formation by L. monocytogenes isolates. The findings may provide insight into how the pathogen persists in some food processing environments. P1-48 Characterization of Listeria monocytogenes Isolates of Imported Cheese Contributed to the National PulseNet Database by the FDA from 2001 to 2008 BABGALEH B. TIMBO, Christine Keys and Karl Klontz Food and Drug Administration, Center for Food Safety and Applied Nutrition, College Park, MD, USA Introduction: Imported foods must meet the same Food and Drug Administration (FDA) standards as domestic foods. Pursuant to regulatory activities, FDA conducts compliance surveillance on imported foods offered for entry into US commerce. The FDA compliance surveillance system helps to detain or refuse entry of foods that are found to be 78 — Abstract Book Poster

IAFP 2009 Program Book and Abstract Book

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