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Fluorocult E. coli O157:H7 Agar (E. coli O157:H7 Agar, Fluorocult)

[所属分类:培养基配方] [发布时间:2021-11-19] [发布人:网站管理员2] [阅读次数:] [返回]

Fluorocult E. coli O157:H7 Agar

(E. coli O157:H7 Agar, Fluorocult)

山东拓普生物工程有限公司培养基配方 http://www.topbiol.com

Composition per liter:

Peptone from casein..........................................20.0g

Agar ..................................................................13.0g

Sorbitol..............................................................10.0g

NaCl....................................................................5.0g

Meat extract ........................................................2.0g

Na2S2O3 ..............................................................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 dis

tilled/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 entero

hemorrhagic (EHEC) Escherichia coli O157:H7-

strains from foods. In contrast to most other E. coli

strains, E. coli O157:H7 shows the following charac

teristics: no sorbitol-cleavage capacity within 48 hr.

and no formation of glucuronidase (MUG-negative/

no fluorescence). Sodium deoxycholate inhibits the

growth of the Gram-positive accompanying flora for

the greater part. Sorbitol serves, together with the pH

indicator bromthymol blue, to determine the degra

dation of sorbitol which, in the case of sorbitol-posi

tive microorganisms, results in the colonies turning

yellow in color. Sorbitol-negative strains, on the oth

er hand, do not lead to any change in the color of the

culture medium and thus proliferate as greenish col

onies. 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. Pro

teus mirabilis in particular, which displays biochem

ical 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-glucu

ronidase- forming pathogens; 4-methylumbellifer

one 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-glucoron

idase. When irradiated with long-wave UV light, no

fluorescence is formed.

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Fluorocult E. coli O157:H7 Agar (E. coli O157:H7 Agar, Fluorocult)