Comparing the Mannitol–Egg Yolk–Polymyxin Agar Plating Method with the Three-Tube Most-Probable-Number Method for Enumeration of Bacillus
cereus Spores in Raw and High-Temperature, Short-Time Pasteurized Milk
The U.S. Food and Drug Administration's Bacteriological Analytical Manual recommends two enumeration methods for Bacillus cereus: (i) standard plate count method with mannitol–egg yolk–polymyxin (MYP) agar and (ii) a most-probable-number (MPN) method with tryptic
soy broth (TSB) supplemented with 0.1% polymyxin sulfate. This study compared the effectiveness of MYP and MPN methods for detecting and enumerating B. cereus in raw and high-temperature, short-time pasteurized skim (0.5%), 2%, and whole (3.5%) bovine milk stored at 4°C for 96 h.
Each milk sample was inoculated with B. cereus EZ-Spores and sampled at 0, 48, and 96 h after inoculation. There were no differences (P > 0.05) in B. cereus populations among sampling times for all milk types, so data were pooled to obtain overall mean values for each
treatment. The overall B. cereus population mean of pooled sampling times for the MPN method (2.59 log CFU/ml) was greater (P < 0.05) than that for the MYP plate count method (1.89 log CFU/ml). B. cereus populations in the inoculated milk samples ranged from 2.36 to
3.46 and 2.66 to 3.58 log CFU/ml for inoculated milk treatments for the MYP plate count and MPN methods, respectively, which is below the level necessary for toxin production. The MPN method recovered more B. cereus, which makes it useful for validation research. However, the MYP plate
count method for enumeration of B. cereus also had advantages, including its ease of use and faster time to results (2 versus 5 days for MPN).
Document Type: Research Article
Food Science Institute, Kansas State University, Manhattan, Kansas 66506, USA
Food Science Institute, Department of Animal Sciences and Industry, Kansas State University, Manhattan, Kansas 66506, USA. firstname.lastname@example.org
Food Science Institute, Department of Animal Sciences and Industry, Kansas State University, Manhattan, Kansas 66506, USA
Department of Food Science, Purdue University, West Lafayette, Indiana 47907-1160, USA
Publication date: March 1, 2011
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