A Study on Selective Broths and Agar Media for the Isolation of Escherichia coliO157:H7 Serotype


Abstract: Modified tryptic soy broth, lauryl sulfate tryptose broth, modified EC broth, sorbitol MacConkey agar and Fluorocult E. coli O157 agar were tested for the recovery of 3 strains of Escherichia coliO157:H7 against E. colitype 1 and Citrobacter freundii as common competitive microflora of raw meat products. Two-stepped trials showed that modified EC broth and lauryl sulfate tryptose broth were superior to modified tryptic soy broth as selective enrichment media while sorbitol MacConkey agar was clearly better than Fluorocult E. coli O157 agar as a selective agar medium. Recovery of E. coli O157:H7 was difficult when selective enrichment broth-growing cohabitant microflora were present at more than 100 folds of E. coliO157. One percent E. coli O157:H7 in the cohabitant flora was the minimum level for recovery. This is probably more important than the minimum recovery rate of culture media and/or conventional culture methods when E. coli O157:H7 exists without competitive microorganisms.

Keywords: E. coli O157:H7, mTS Broth, mEC Broth, LST Broth, SMAC Agar.

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