Growth rate of salmonellas in Rappaport-Vassiliadis broth (RV) decreased with higher temperature when incubated at 40, 42 and 43 degrees C. Home-made RV and RV-Merck were less inhibitory than RV-Oxoid and RV-lab m. At 43 degrees C growth of all strains of Salmonella dublin were almost completely inhibited in all types of RV. In home-made RV and RV-Merck incubated at 42 degrees C, Salm. dublin was not inhibited any more than other serotypes tested. Variations in growth rate between different types of RV could be explained by differences in concentration of MgCl2. RV with higher MgCl2-concentration were most inhibitory. It is proposed that RV should be incubated at 41.5 +/- 0.5 degrees C (42.0 +/- 0.1 degrees C in a waterbath) and that the amount of MgCl2.6H2O should be approximately 28.6 g/l of the ready-to-use medium, which corresponds to the formula in the original description.
Three media for isolation of Bacillus cereus from foods were compared: mannitol-egg yolk-polymyxin (MYP) agar, polymyxin pyruvate-egg yolk-mannitol-bromothymol blue agar (PEMBA) and non-selective blood agar. Twenty-six of 45 samples of different reconstituted and incubated dry food products and 18 of 29 samples of milk and cream (incubated overnight) contained B. cereus. None of the media performed significantly better than the others as regards quantitative recovery or selectivity.
Twelve laboratories from 7 countries compared the productivity of refrigerated (72 h at 5 to 10°C) preenrichment and enrichment broth cultures with a standard cultural procedure for detection of Salmonella in 466 naturally contaminated low and high moisture foods. Refrigerated preenrichment and enrichment cultures identified 92.5 and 94.2% of contaminated samples, respectively. Variations in the ability of laboratories to successfully recover salmonellae under refrigeration test conditions were notable. Three laboratories found complete agreement between results by the standard and refrigeration test procedures and 5 additional laboratories reported >90% accuracy; lowest recovery rate for combined refrigeration results was 77%. Sensitivity of the refrigeration techniques was markedly greater with low than high moisture foods where the latter contributed all but two of the 62 false-negative results encountered in this study. Ability of individual laboratories to recover Salmonella from refrigerated preenrichment and enrichment broth cultures was not significantly different for given food categories. Productivity of paired enrichment-plating media differed widely with food type. Selective enrichment in tetrathionate brilliant green and plating on bismuth sulfite agar showed greatest sensitivity for isolation of Salmonella in high but not in low moisture foods where productivity of the 4 enrichment-plating conditions used in this study was comparable. Results on recoverability of Salmonella from refrigerated broth cultures concur with findings of an earlier comparative study and strongly support incorporation of this novel approach in standard cultural methods for detection of Salmonella in foods.
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