Modified sorbitol MacConkey agar for the rapid isolation of Escherichia coli O157:H7

  • Jung, Byeong-yeal (Department of Bacteriology, National Veterinary Research and Quarantine Service, MAF) ;
  • Jung, Suk-chan (Department of Bacteriology, National Veterinary Research and Quarantine Service, MAF) ;
  • Lee, Na-kyung (Department of Bacteriology, National Veterinary Research and Quarantine Service, MAF) ;
  • Cho, Seong-kun (Department of Bacteriology, National Veterinary Research and Quarantine Service, MAF) ;
  • Cho, Dong-hee (Department of Bacteriology, National Veterinary Research and Quarantine Service, MAF) ;
  • Her, Moon (Department of Bacteriology, National Veterinary Research and Quarantine Service, MAF) ;
  • Yoon, Yong-dhuk (Department of Bacteriology, National Veterinary Research and Quarantine Service, MAF) ;
  • Kim, Bong-hwan (College of Veterinary Medicine, Kyungpook National University)
  • Received : 1999.08.10
  • Published : 1999.09.01

Abstract

Unlike most Escherichia coli strains, E coli O157 : H7 didn't ferment sorbitol within 24h of incubation and showed a negative reaction for $\beta$-glucuronidase. We developed a new medium for the rapid isolation of E coli O157 : H7 using sorbitol MacConkey agar with cefixime, potassium tellurite and 4-methylumbelliferyl-${\beta}$-D-glucuronide (MUG) as a primary plating medium. The addition of $20{\mu}g/ml$ of vancomycin in enrichment broth for E coli O157 : H7 inhibited lots of Gram positive bacteria. Three strains (10.3%) of 29 non-O157 E coli strains and 3 strains (8.3%) of 36 Salmonella spp were inhibited at the $0.05{\mu}g/ml$ of cefixime and 23 strains (79.3%) of 29 non-O157 E coli strains and 12 strains (33.3%) of 36 Salmonella spp were inhibited at the $2.0{\mu}g/ml$ of potassium tellurite. But none of the E coli O157 : H7 was affected at these concentration. The addition of MUG at $100{\mu}g/ml$ level to sorbitol MacConkey agar with cefixime and potassium tellurite (CTM-SMAC) aided in the rapid isolation of E coli O157 : H7 from samples by checking sorbitol-negative and $\beta$-glucuronidase negative phenotypes simultaneously. In conclusion, inoculation of a positive in the O157 screening test from enrichment broth on CTM-SMAC appeared to be a rapid, cost-effective and sensitive method for the isolation of E coli O157 : H7.

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Acknowledgement

Supported by : Korea Agricultural Rearch and Development Promotion Center