Method to Isolate Escherichia coli O157:H7 from Food

Abstract

A medium for direct overnight isolation of hemorrhagic colitis (HC) strains of Escherichia coli from foods has been developed. It is a direct plating medium incorporating tryptophan (as tryptone), sorbitol, an indicator dye and a fluorogenic substrate for diagnostic purposes. Sodium chloride is included to raise the upper temperature limit for growth and a bile salt concentration lower than that usual for E. coli media but still inhibitory to non-enteric organisms is used. Colonies of HC strains grown overnight at 44.5°C on membrane filters placed on the medium are blue. Subsequent indole staining of the membranes yields red positive colonies. Replicate colonies are confirmed serologically. In contrast, E. coli Type I colonies are yellow and give apparently negative indole reactions. Recovery of HC organisms from artificially contaminated ground beef is ≥90%.

Growth of pure cultures of Verocytotoxin-producingEscherichia coliin a range of enrichment media

“…Previous studies have used EC and mEC medium supplemented with novobiocin for the detection of E. coli O157 from foods (Szabo et al 1986;Bennett et al 1995;Hara-Kudo et al 1999). To detect E. coli O26 and O157 in foods, HaraKudo et al (2000) reported that enrichment in mEC + n at 42°C for 18 h was a successful combination.…”

Intestinal Shiga Toxin-Producing Escherichia coli Bacteria Mitigate Bovine Leukemia Virus Infection in Experimentally Infected Sheep

“…The prefiltrate was decimally diluted in PT, and appropriate dilutions (typically 10 Ϫ1 and 10 Ϫ2 of the prefiltrate) were filtered onto hydrophobic grid membrane filters (HGMFs) (Isogrid membranes; Neogen, Lansing, MI) using a spreadfilter (Filtaflex, Almonte, ON, Canada) and a vacuum manifold. HGMFs were incubated at 37°C face up on hemorrhagic colitis agar (50), modified from the original formulation, to detect all STEC bacteria by the omission of 4-methylumbelliferyl-␤-D-glucuronide (MUG), 1% cefsulodin, and 0.1% potassium tellurite, as these supplements were specific to the isolation of the O157:H7 serotype. Colonies on each HGMF were replicated onto another HGMF using an HGMF replicator/inoculator system (Filtaflex).…”

Detection and Characterization of Verocytotoxin-Producing Escherichia coli by Automated 5′ Nuclease PCR Assay

“…by using a spread filter (Filtaflex Ltd., Almonte, Ontario, Canada). The filters were placed on modified hemorrhagic colitis (mHC) agar (44) and incubated overnight at 37°C. One replica of the colonies on the HGMF was placed onto another HGMF with a replicator (Filtaflex Ltd).…”