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The random amplified polymorphic DNA (RAPD) band patterns from 23 Salmonella spp. produced by use of an oligonucleotide primer (called du primer) designed on the basis of the N-terminal sequence of dulcitol 1-phosphate dehydrogenase (5'-GTGGTGACCCAGGATGGCCAGGTG-3') were different from those from 16 non-Salmonella spp. The bands at 460 and 700 bp were produced in all Salmonella strains tested. These RAPD fragments obtained from Salmonella typhimurium strongly hybridized with the corresponding RAPD bands from the other strains of Salmonella, but not with those from non-Salmonella spp. in Southern blot analysis. The RAPD bands were detected by ethidium bromide staining even when genomic DNA prepared from as few as 2.8 x 10(3) cells was used. The minimum detectable cell number in the initial inoculum of S. typhimurium was 4 x 10(-1) CFU/25 g of raw beef after the preenrichment in Enterobacteriaceae enrichment mannitol (EEM) broth for 6 h and the selective enrichment in dulcitol-magnesium chloride-pyridinesulfonic acid-brilliant green-novobiocin (DMPBN) medium for 18 h at 42 degrees C. Seven raw foods inoculated with S. typhimurium at numbers from 4 x 10(-1) to 2.6 x 10(2) CFU/25 g of food were positive in both the RAPD analysis and the conventional culture method.

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A bioluminescence assay carried out with a photon-counting TV camera was evaluated for rapid enumeration of viable bacterial counts. The test sample was filtered through a membrane filter, and the membrane filter retaining bacteria was incubated at 37 degrees C for 6 h on a filter paper soaked with nutrient broth supplemented with 0.5% NaCl. The membrane filter was then subjected to a bioluminescence reaction, and the intensity of light and numbers of light emission points on the filter were measured with a photon-counting TV camera. The light intensity measured on seven different bacteria correlated with initial viable counts; the correlation coefficient was calculated to be 0.89. The number of light emission points measured on Escherichia coli also correlated with the initial viable counts (r = 0.81) in a range from 1 to 100 CFU. Presumptive bacterial counts by the present bioluminescence assay determined on 79 samples of vegetables and 122 samples of environmental water correlated well with the viable counts obtained by the conventional plating method, with correlation coefficients of 0.87 and 0.82, respectively.

The present study aimed to evaluate in vitro anti-adherence abilities of the probiotic potential of three selected lactic acid bacteria (LAB) strains isolated from fermented broken rice with two foodborne pathogenic bacteria to Caco-2 cells. Lactobacillus plantarum Ban Pra Doke 110 was the most adherent strain with an adherence of 17.66% at a concentration of added bacterial cells of 2.0 × 10 8 cfu/mL (multiplicities of infection 100). In the exclusion, competition and displacement tests, Lact. plantarum PD 110 showed the most anti-adherence abilities against Salmonella Typhimurium American Type Culture Collection 13311 and Listeria monocytogenes ScottA to Caco-2 cells. Moreover, the presence of its spent culture supernatant exhibited the highest decrease in the percentage numbers of the adherent pathogenic bacteria used in all tests. The effectiveness of each LAB strain was tested to adhere to Caco-2 cells or to prevent the adherence of the test pathogenic bacteria varied widely depending on the genus and species, source of origin, and assay condition, as well as adherent-promoting factors. PRACTICAL APPLICATIONSFoodborne pathogen infection to the human intestinal epithelial surface cells is a critical step for the survival and cause foodborne illness. The anti-adherent assessment of novel probiotic is of importance for the inhibition of pathogen infections. Lactobacillus plantarum PD 110 isolated from fermented broken rice could be one of these good candidates. The demonstrated in vitro anti-adherent activity of Lact. plantarum PD 110 to Caco-2 cells recommends its possible application as a probiotic candidates in order to inhibit the adherence of Salmonella Typhimurium and Listeria monocytogenes to the human gastrointestinal tract. Therefore, this strain can be considered as a novel potential starter culture to improve the quality and safety of functional foods. bs_bs_banner Journal of Food Safety ISSN 1745-4565 IN VITRO ANTI-ADHERENT ASSESSMENT S. SRIBUATHONG, J. SAENGPRAKAI and S. TREVANICH

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