Analysis of the Quality Difference of Xylose Lysine Deoxycholate Agar for Food Testing
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Abstract:
In order to enrich the quality control strains during the acceptance of media for food microbiology testing in China and improve the quality of commercial culture media, the medium acceptance method specified in GB 4789.28-2013 was used in this experiment. Salmonella typhimurium ATCC 14028, Shigella fowlerii CMCC 51572, Staphylococcus aureus ATCC6538 and Escherichia coli ATCC 25922 were used as the references. Six strains of Salmonella typhimurium, one strain of Shigella fowleri, four strains of Staphylococcus aureus and five strains of Escherichia coli were selected for evaluating the physical indexes such as appearance, pH value and moisture content, as well as the microbial indicators such as growth rate and selectivity of four brands of XLD. The results showed that the colors of dry powders of four medium brands, A, B, C and D, were pink, light pink, earthy yellow and pinkish white. Their moisture contents were 5.55%, 5.92%, 5.46% and 5.94%, respectively. The dosages were 5.54, 5.89, 5.69, and 5.70 g in 100 mL respectively. All the pH values were 7.4. The growth rates of the six Salmonella typhimurium strains and the Shigella fowleri strain on the four brands of media were not lower than 0.7, whilst none of the four of Staphylococcus aureus strains grew, and all the five Escherichia coli strains had a growth index G lower than 5. In summary, the four brands of XLD all conformed to GB 4789.28-2013, the strain selected for this experiment can be used as a supplementary strain for the acceptance of XLD quality control strains.
