IAFP 2009 Program Book and Abstract Book - AB89

Significance: Moisture enhancement of beef via needle injection can transfer E. coli O157:H7 to the interior of whole muscle cuts when either the meat surface or brine solution is contaminated with the pathogen. The data may be useful in risk assessments for nonintact meat products. P1-74 Transfer of Escherichia coli O157:H7 to Beef Steaks through Needle Tenderization NIKOS CHORIANOPOULOS, Ifigenia Geornaras, George-John E. Nychas, Keith E. Belk, Gary C. Smith and John N. Sofos Colorado State University, Dept. of Animal Sciences, Fort Collins, CO, USA Introduction: Cross contamination is one of the most important contributing factors in foodborne illnesses. Mechanical tenderization of meat may cause transfer of foodborne pathogens to subsequently tenderized product. However, there is limited information on cross-contamination during tenderization. Such products are classified as non-intact and if contaminated with Escherichia coli O157:H7 are considered adulterated. Purpose: This study evaluated transfer of contamination of E. coli O157:H7 from surface-inoculated steaks to subsequently processed non-inoculated steaks through needle tenderization. Methods: Beef steaks (7.5 × 6.25 × 3 cm; eye of round muscle) were surface-inoculated with 6 to 7 log CFU/cm2 rifampicin-resistant E. coli O157:H7 (mixture of 8 strains). After inoculation, needle tenderization was performed using a hand-operated needle tenderizer (48 needles on a surface of 80 × 15 mm). After needle tenderization of each inoculated steak, six additional non-inoculated steaks were tenderized in sequence using the same tenderizer without sanitation. Steaks were tenderized one (single-pass tenderization), two (double-pass) or three (triple-pass) times. Samples were excised from the surface (0 to 0.1 cm depth) of each steak, and total bacterial (Tryptic Soy Agar, TSA) and E. coli O157:H7 (TSA with 100 mg/l rifampicin) populations were determined before and after tenderization. The study was replicated twice, with two samples each time. Results: The results indicated that E. coli O157:H7 cells were transferred onto all non-inoculated steaks following needle tenderization. More specifically, the transfer of E. coli O157:H7 on the surface of non-inoculated steaks was 5.35 log CFU/ cm2 for the first cross-contaminated steak, 4.69 log CFU/cm2 for the second, 4.65 log CFU/cm2 for the third, 4.45 log CFU/ cm2 for the fourth, 3.91 log CFU/cm2 for the fifth, and 3.81 log CFU/cm2 for the sixth after single-pass tenderization. The transfer of E. coli O157:H7 following double-pass tenderization was 5.29 log CFU/cm2 for the first cross-contaminated steak, 4.57 log CFU/cm2 for the second, 4.45 log CFU/cm2 for the third, 4.28 log CFU/cm2 for the fourth, 3.79 log CFU/cm2 for the fifth and 3.61 log CFU/cm2 for the sixth. Similar trends in results were observed for triple-pass tenderization. Significance: The study provided quantitative data for transfer of E. coli O157:H7 from a surface-inoculated steak to subsequent non-inoculated steaks and will be useful in risk assessments for non-intact beef products. P1-75 Selection and Characterization of Cellulose Deficient Mutants of Shiga-toxin Producing Escherichia coli DSC BYONG KWON YOO, Tod Stewart, Jean Guard-Bouldin, Michael Musgrove, Richard Gast and Jinru Chen University of Georgia, Food Sci & Tech, Griffin, GA, USA Introduction: Shiga-toxin producing Escherichia coli (STEC) are known to have several defense mechanisms, one of which is the production of protective extracellular substances, such as cellulose. Purpose: The goal of this study was to prepare pairs of STEC cultures useful for future research designed to address the role of cellulose in protecting the cells of STEC against environmental stress. Methods: Spontaneous cellulose deficient mutants, 19D and 49D, were isolated, and the identities of the mutants and their respective parents, 19B and 49B, were confirmed. Growth characteristics of the STEC strains were determined using the phenotypic microarray (PM) technology. Results: The two members within each STEC pair shared the same serotypes and similar PFGE profiles. Profound morphological differences were found, however, between the two types of cells. Strain 49B and 49D grew better than 19B and 19D in all three PM panels used in the study. The growth of 19B vs. 19D and 49B vs. 49D were significantly different only in the presence of two antibiotics on the antibiotic panel. On the osmolyte panel, 49D had significantly poorer growth than 49B only in broth supplemented with 4 different osmolytes. Strain 19D, however, grew similarly to 19B under these conditions. On the pH panel, significant differences in the growths of 19B and 19D were observed only in broth with pH 4.5 or 9.5 and supplemented with 3 to 4 different amino acids or trimethylamine-N-oxide. Strain 49B grew better than 49D only in broth with pH 9.5 and supplemented with five different amino acids. Additionally, 19B and 49B grew better than 19D and 49D, respectively, in broth supplemented with X-caprylate. Significance: The two members of each STEC pair shared similar growth characteristics except under extreme stress. These strains could be useful in investigating the role of cellulose in protecting the cells of STEC against environmental stress. P1-76 Tandem Repeat Stability in Escherichia coli O157:H7 is Dependent on the Duration and Type of Environmental Stress MICHAEL B. COOLEY USDA-ARS, Produce Safety and Microbiology, Albany, CA, USA Introduction: Escherichia coli O157:H7 is an enteric pathogen that can survive in low numbers in water, in soil and on plants. Multilocus variable number tandem repeat analysis (MLVA) has become the method of choice for high-throughput subspecies typing of E. coli O157:H7. Comparisons of hundreds of isolates from environmental and clinical sources indicate considerable variation at 11 loci, with some loci apparently changing faster than others. Purpose: The rate of mutation at these loci is of considerable importance to source tracking. Methods: Mutation rates at these same loci have been measured by us and other research groups during repeated serial passaging on complete media. Since conditions in the environment are very different from those in the animal gut or Abstract Book — 89 Poster

IAFP 2009 Program Book and Abstract Book

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