Food Protection Trends - February 2010 - 95

refrigeration, heat and high isostatic pressure) stresses. the technique was compared to plate counting on nonselective medium: tryptic soy agar with yeast extract (tsaye); and selective media: tsaye with sodium chloride (tsaye+naCl) and sorbitol MacConkey agar (sMaC). Results: While E. coli o157:H7 counts declined from 7.0 to ca. 6.0 log CFU/ml with sodium benzoate (0.1%, 42 h) and vinegar (to reach pH 4.0, 42 h), the organism was totally inactivated by sodium hypochlorite (150 ppm free chlorine, 30 s before sample processing). Heat (68°C, 15 s) caused a ca. 3.5-CFU/ml reduction, whereas high pressure (400 MPa, 2 min, 20°C) decreased counts by 3.0 log CFU/ml. In general, counts on selective media were similar to those on tsaye, except for the pressure-treated sample, whose counts on tsaye+naCl and sMaC were, respectively, ca. 1.5 and 1 log CFU/ml lower than those on tsaye, which suggests a large injured cell population that agrees with flow cytometry results. syto9-PI staining enabled good separation and identification of live, injured and dead bacteria; and gave counts (determined by means of a calibrated microsphere suspension) higher than those estimated by plate counting. Conclusions: Flow cytometry can improve the knowledge about physiological state of pathogenic bacteria after food processing and preservation treatments. P1-19 Evaluation of a Rapid Two-day Isolation Method for Salmonella Using Oxoid ONE Broth–Salmonella and Brilliance Salmonella Agar Jeff J. Koziczkowski, Dorn L. Clark, Roy P Radcliff, Christine Hilbert, Jonathan Cloke and aLastaIR tHoMas, oxoid, Wade Road, Basingstoke, RG24 8PW, United Kingdom Introduction: Salmonella is a Gram-negative, rod-shaped, motile bacterium with a widespread occurrence in animals, especially poultry and swine. additional sources of this organism include raw meat, raw poultry, and raw seafood, to name only a few. Detection is critical as Salmonella is the most frequently reported cause of food borne illness (within the Usa, 40,000-50,000 cases are reported annually) and the infectious dose can be as low as 1–10 CFU/g. this study evaluated the oxoid Salmonella rapid culture method which combines oxoid one Broth-Salmonella and Brilliance™ Salmonella agar in a simple protocol, for the detection of Salmonella in food within 2 days. Rational: 25 g samples of minced beef, minced chicken, lettuce, shrimp and shell eggs were inoculated with Salmonella serovars at a level of ~1 CFU/25 g. samples were then enriched in oxoid one Broth-Salmonella at 42°C for 16–24 h before plating a 10 µl loop full onto Brilliance Salmonella agar and incubating at 37°C for 24–26 h. the oxoid Salmonella rapid culture method was compared to either the UsDa or FDa established protocols depending on the food matrix. the specificity of the methods was evaluated using multiple Salmonella serovars (n = 100) or closely related bacterial species (n = 30). Results: When selected foods were inoculated with Salmonella serovars at a level of ~1 CFU/25 g there was no difference in sensitivity between the oxoid Salmonella rapid culture method and the reference methods. When specificity was evaluated 96/100 Salmonella serovars were identified using this method and 29/30 of the nonSalmonella showed no growth or atypical growth. Conclusions: enriching samples using one Broth-Salmonella and plating on Brilliance Salmonella agar reduced time to detection to as little as 38 h, compared to the FDa and UsDa reference methods which took 4 days. Identification of presumptive positive colonies on Brilliance Salmonella agar can be conducted rapidly using the oxoid Salmonella Latex kit, to give a confirmed result in 2 days. P1-20 An Improved Medium for the Enumeration of Coagulase-Positive Staphylococci from Foods: Oxoid Brilliance™ Staph 24 Agar Mark Gibson, Kim Kirby and JonatHan M. CLoKe, oxoid, Wade Road, Basingstoke, Rg24 8PW, United Kingdom Introduction: Contamination of foods both pre- and post-production with coagulase positive staphylococci (CPs) is a potential cause of serious food poisoning. although Baird-Parker agar with egg yolk and tellurite (BPa) is traditionally the most commonly used medium for the enumeration of CPs from foodstuffs according to Iso 6888-1, the 48 h incubation period and highly variable colony morphology of typical and atypical isolates are widely seen as disadvantages. oxoid Brilliance staph 24 agar, a new chromogenic medium for the enumeration of CPs within 24 h was evaluated as an alternative to BPa. Rational: eighty routine food samples covering cooked vegetables, sweets and chocolate, powdered flavourings, meat sauce and cheeses were analysed. samples were prepared and decimally diluted according to the laboratories standard method before spreading 0.25 ml of 10-1 dilutions over single plates of acumedia BPa and Brilliance staph 24 agar. Inoculated BPa was incubated at 37 ± 1°C for 48 ± 2 h. Brilliance staph 24 agar was incubated at 37 ± 1°C for 24 ± 2 h. typical and atypical colonies on BPa and presumptive positive (blue) colonies on Brilliance staph 24 agar were sub-cultured onto Plate Count agar (37 ± 1°C for 24 ± 2 h) before confirming CPs by the tube coagulase test. FEBRUARY 2010 | FOOD PROTECTION TRENDS

Food Protection Trends - February 2010

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