Fluorocult

Fluorocult^® E. coli 0157:H7 Agar

EMD Cat. No. 1.04036.0500

500 g

Selective agar for the isolation and differentiation of enterohemorrhagic (EHEC) Escherichia coli 0157:H7-strains in food.

Description
Four different intestinal-pathogenic E. coli types are presently known: besides the infant-pathogenic (EPEC), the enterotoxin-forming (ETEC), and the entero-invasive (EIEC) E. coli types, in 1982 the so-called enterohemorraghic (EHEC) 0157:H7 E. coli strains were first detected following the ingestion of hamburgers in the United States. Enterohemorrhagic E. coli lead to the formation of toxins - following their passage from the intestine into the blood circulation - resulting in life-threatening extraintestinal complications in the form of the hemolytic uremic syndrome (HUS) and thrombotic-thrombocytopenic purpura (TTP) in 3-20 % of all cases.

In contrast to most other E. coli strains, E. coli 0157:H7 shows the following characteristics:
No sorbitol-cleavage capacity within 48 h.
No formation of glucuronidase (MUG-negative/no fluorescence).

Mode of Action	Preparation
Quality Control	Typical Composition (g/liter)
Literature	Picture/Image

Mode of Action
Sodium deoxycholate inhibits the growth of the Gram-positive accompanying flora for the greater part. Sorbitol serves, together with the pH indicator bromothymol blue, to determine the degradation of sorbitol which, in the case of sorbitol-positive microorganisms, results in the colonies turning yellow in color. Sorbitol-negative strains, on the other hand, do not lead to any change in the color of the culture medium and thus proliferate as greenish colonies. Sodium thiosulfate and ammonium iron(III) citrate result in black-brown discoloration of the agar for colonies, in the presence of hydrogen-sulfide-forming pathogens, precipitating iron sulfide.

Proteus mirabilis in particular, which displays biochemical properties similar to those of E. coli 0157:H7, can thus be very easily differentiated from E. coli 0157:H7 on account of the brownish discoloration. 4-methylumbelliferyl-β-D-glucuronide (MUG) is converted into 4-methylumbelliferone by βD-glucuronidase- forming pathogens; 4-methylumbelliferone fluoresces under UV light. The activity of β-D-glucuronidase is a highly specific characteristic of E. coli. In contrast to most E. coli strains, E. coli 0157:H7 is not capable of forming β-D-glucoronidase. When irradiated with long-wave UV light, no fluorescence is formed.

Typical Composition (g/liter)
Peptone from casein 20.0; meat extract 2.0; yeast extract 1.0; sorbitol 10.0; ammonium iron(III) citrate 0.5;
4-methylumbelliferyl-β-D-glucuronide 0.1; sodium chloride 5.0; bromothymol blue 0.025; sodium thiosulfate 2.0; sodium deoxycholate 1.12; agar-agar 13.0.

Preparation
Suspend 55 g in 1 liter of purified water and autoclave (15 min at 121°C).
pH: 7.4 ± 0.2 at 25°C.
The plates are clear and blue-green.
Incubation: 24 h at 35°C aerobically.

Quality control

Test strains	Growth	Colony color	MUG	Sorbitol
Escherichia coli 0157:H7	good / very good	colorless	-	-
Escherichia coli ATCC 25922	fair / good	yellow	+	+
Proteus mirabilis ATCC 14273	good / very good	brown	-	-
Shigella sonnei ATCC 11060	good / very good	colorless	+	-
Enterobacter aerogenes ATCC 13048	good / very good	yellow	-	+
Salmonella typhimurium ATCC 14028	good / very good	yellow w / black centre	-	+
Enterococcus faecalis ATCC 19433	none

Additives

EMD Cat. No.	Product	Pack Size
1.10266.0500	Lauryl Sulfate Broth	500 g
1.13203.0001	UV Lamp (366 nm)	1 ea

Literature

SZABO, R.A., TODD, E.C., EAN, A.: Method to isolate E. coli 0157:H7 from food. - J. Food Prot., 10; 768-772 (1986).


E.coli O157:H7, E.coli, Serratia marcescens	E.coli O157:H7, E.coli, Serratia marcescens