IAFP 2009 Program Book and Abstract Book - AB88

Methods: E. coli O157:H7 was inoculated onto lettuce, or ground beef, or into TSB and incubated at 37°C for 24 h. RNA from these cells was extracted. Reverse-transcriptase real-time PCR was used to evaluate expression of six virulence genes (stxII, eae, ehx, espA, ihaA, and rfbE) and one standard gene (gnd) in ground beef, on lettuce, or in TSB. Cycle threshold counts of each gene in TSB were used to construct standard curves, and expression of genes from cells grown on lettuce or ground beef were fitted to the curve. These values were measured against expression of gnd on lettuce or ground beef, and ratios were analyzed for significant differences (P < 0.05) in expression of genes based on commodity. Results: The expression of virulence factors rfbE (O157-antigen) and ehx (hemolysin) were significantly higher when E. coli O157:H7 was grown in ground beef than on cut lettuce. No differences in expression of stxII (shiga toxin 2), eae (intimin), espA (type III secretion filament), or ihaA (adherence factor) were observed when E. coli O157:H7 cells were grown on lettuce or ground beef. Significance: These data indicate that the growth environment provided by iceberg lettuce supported statistically similar levels of expression of four of six virulence factors of E. coli O157:H7 as ground beef, indicating that the growth environment may not be the sole basis for severe illness observed in previous outbreaks associated with consumption of leafy greens. P1-72 Heat Resistance of Seven Pathogenic STEC Serotypes, Including O157:H7, in Single Strength Apple Juice ELENA ENACHE, Emily Mathusa, Philip H. Elliott and Glenn Black GMA, Science Operations, Washington, D.C., USA Introduction: Without diminishing the importance of Escherichia coli O157:H7 as a major cause of disease worldwide, several researchers showed that non-O157 STEC serotypes make a significant contribution to the overall disease burden. The number of human illnesses due to non-O157 Shiga toxin-producing E. coli (STEC) infection has increased in the past decade worldwide. Pathogenic non-O157 STEC may pose a significant risk to public health. Current interventions for STEC in processed food are based on E. coli O157:H7. To date, little research has focused on the control of non-O157 STEC in foods. Purpose: To determine the heat resistance of six non-O157 STEC serotypes relative to E. coli O157:H7, as a means of assuring adequate processing parameters for the new pathogen in single strength apple juice. Methods: The heating data was obtained using an immersed coil apparatus, equilibrated at 56, 60, and 62C. Inoculum concentration in juice, prior to inactivation, was approximately 106 to 107 CFU/ml. Heat-treated samples (500 µl) were collected at timed intervals in glass vials, immediately cooled in an ice water bath, diluted using 0.1% peptone, and plated on TSA with a spiral plater. Inoculated plates were incubated for 48 h at 35°C. Colony counts were obtained using the Q count system. Results: While serotype O26 presented the lowest D-values at all temperatures (D56C = 2.5 min; D60C = 0.52 min and D62C = 0.28 min), serotypes O145 and O45 revealed the highest D56C (4.7 min and 4.3 min, respectively) amongst the six non-O157 serotypes studied, although it was significantly lower (P < 0.05) than that of E. coli O157:H7 (D56C = 8.51 min) in the same conditions. At 60°C E. coli O157:H7 and O103 presented the highest D-values (0.99 and 0.94 min respectively), followed by O45 and O145. In general, E. coli O157:H7 revealed similar or higher D-values than the six non-O157 STEC serotypes studied in apple juice. Significance: Present data show that the interventions that address E. coli O157:H7 in apple juice would be effective against non-O157 STEC as well. P1-73 Translocation of Escherichia coli O157:H7 during Needle Injection for Moisture Enhancement of Meat DSC SHIVANI GUPTA, Ifigenia Geornaras, Lawrence D. Goodridge, Kendra K. Nightingale, Keith E. Belk, Gary C. Smith and John N. Sofos Colorado State University, Dept. of Animal Sciences, Fort Collins, CO, USA Introduction: Outbreaks linked to consumption of nonintact meat products contaminated with Escherichia coli O157:H7 indicate that processing may introduce pathogens into the interior of the meat. Such contamination may survive if the product is undercooked. Purpose: This study evaluated quantitative transfer of E. coli O157:H7 during moisture enhancement of beef under two contamination scenarios. Methods: In the first contamination scenario, beef knuckles (approximately 4 kg) were surface-inoculated (5 log CFU/g) with nonpathogenic rifampicin-resistant E. coli O157:H7 (5-strain mixture). The meat was then injected, with a hand operated single-needle brine injector, with either sterile distilled water (control) or a brine solution (NaCl [5.5%] and sodium tripolyphosphate [2.75%]) at seven locations per knuckle. In the second contamination scenario, the water and brine solution were inoculated (3 to 4 log CFU/ml) with E. coli O157:H7 and these were used for needle injection. Knuckles were weighed before and after injection and percent increase in weight was determined. One core (8 cm diameter) sample per knuckle was excised parallel to the direction of needle injection, using a coring device. Core samples were surfacedecontaminated with hot water (80°C, 60 s), cooled (4°C, 15 min), and cut into six sections (1 through 6) of 1-cm (sections 1 through 3), 2-cm (sections 4 and 5), and 3- to 10-cm (section 6) thickness, while keeping the knife and cutting board sterile between different cuts. Sections were analyzed (2 to 3 replicates) for E. coli O157:H7 by plating on Tryptic Soy Agar with rifampicin (100 µg/ml). The purge generated following injection of each knuckle was also analyzed for the pathogen. Results: The percentage gain in product weight following injection with water or brine solution was 3 to 10%. The purge released following injection with water or brine solution had E. coli O157:H7 levels of 6.2 log CFU/ml (scenario 1) and 3.1 to 3.6 log CFU/ml (scenario 2). E. coli O157:H7 was recovered from all sections of water- and brine-injected samples under both contamination scenarios, with similar counts obtained for the water and brine treatments. Higher counts of the pathogen were obtained in all sections under scenario 1 (1.9 to 3.6 log CFU/g) than scenario 2 (0.6 to 1.6 log CFU/g). Within each contamination scenario, similar counts were obtained between all sampled sections. 88 — Abstract Book Poster

IAFP 2009 Program Book and Abstract Book

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