Fluorocult ® E. coli O157:H7 Agar

[所属分类:培养基配方] [发布时间:2021-3-2] [发布人: ] [阅读次数:] [返回]

Fluorocult ® E. coli O157:H7 Agar

培养基配方

Composition per liter:
Peptone from casein....................................................................20.0g
Agar............................................................................................13.0g
Sorbitol .......................................................................................10.0g
NaCl..............................................................................................5.0g
Meat extract..................................................................................2.0g
Na 2 S 2 O 3 ........................................................................................2.0g
Sodium deoxycholate..................................................................1.12g
Yeast extract..................................................................................1.0g
Ammonium ferric citrate ..............................................................0.5g
4-Methylumbelliferyl-β- D -glucuronide........................................0.1g
Bromthymol Blue.....................................................................0.025g
pH 7.4 ± 0.2 at 25°C
Source: This medium is available from Merck.
Preparation of Medium: Add components to distilled/deionized water and bring volume to 1.0L. Mix thoroughly. Autoclave for 15 min at 15 psi pressure–121°C. Cool to 45°–50°C. Pour into sterile Petri dishes.
Use:  For the isolation and differentiation of enterohemorrhagic (EHEC) Escherichia coli O157:H7 strains from foods. In contrast to most other E. coli strains, E. coli O157:H7 shows the following characteristics: no sorbitol-cleavage capacity within 48 hr and no formation of glucuronidase (MUG-negative/no fluorescence). Sodium deoxy-cholate 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 O157:H7, can thus be very easily differentiated from E. coli O157:H7 on account of the brownish discoloration. 4-Methylumbelliferyl-β- D -glucuronide (MUG) is converted into 4-methylumbelliferone by β- D -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 O157:H7 is not capable of forming β- D - glucoronidase. When irradiated with long-wave UV light, no fluorescence is formed.