Selenite cystine broth (7283)
BUFFERED LISTERIA ENRICHMENT BROTH BASE (7675)
Buffered Listeria Enrichment Broth Base (BLEB)
is used with supplements for selective enrichment ofListeria spp
Product Summary and Explanation
, described first in 1926 by Murray, Webb, and Swann,1 is an extensive problem in
public health and food industries. This organism has the ability to cause human illness and death, particularly
in immunocompromised individuals and pregnant women.2 Epidemiological evidence from outbreaks of
listeriosis has indicated that the principle route of transmission is via consumption of foodstuffs contaminated
with Listeria monocytogenes
.3 Implicated vehicles of transmission include turkey, frankfurters, coleslaw,
pasteurized milk, Mexican style cheese, and pate′.4
Buffered Listeria Enrichment Broth, a modification of the formula by Lovett et al.5 was developed aftersubsequent work concluded that enrichment properties can be improved by increasing the buffering capacityof the medium with the addition of disodium phosphate. Buffered Listeria Enrichment Broth Base is basedupon the latest FDA recommendations in which the medium is supplemented with selective agents after aninitial 4 hour, non-selective, pre-enrichment.6
Principles of the Procedure
Enzymatic Digest of Casein, Enzymatic Digest of Soybean Meal, and Yeast Extract provides nitrogen,
vitamins, and minerals in Buffered Listeria Enrichment Broth Base. Dextrose is the carbohydrate source.
Sodium Chloride maintains osmotic balance of the medium. Monopotassium Phosphate, Dipotassium
Phosphate, and Disodium Phosphate are the buffering agents. Sodium pyruvate is added aseptically as an
oxygen scavenger. Nalidixic acid, Acriflavin and Cycloheximide are added as selective agents after an initial
four-hour pre-enrichment. Nalidixic Acid inhibits growth of Gram-negative organisms. Acriflavin inhibits Gram-
positive bacteria. Cycloheximide is used to inhibit growth of saprophytic fungi. The delay in adding these
agents is intended to facilitate resuscitation, repair, and growth of injured Listeria
Formula / Liter
BLEB Base Supplements/225mL
Dextrose. 2.5 gSodium Chloride . 5 gMonpotassium Phosphate . 1.35 gDipotassium Phosphate. 2.5 gDisodium Phosphate. 9.6 gFinal pH: 7.3 ± 0.2 at 25°CFormula may be adjusted and/or supplemented as required to meet performance specifications.
1. For Laboratory Use.
2. IRRITANT. Irritating to eyes, respiratory system, and skin.
1. Dissolve 47 g of the medium in one liter of purified water.
2. Heat with frequent agitation and boil for one minute to completely dissolve the medium.
3. Autoclave at 121°C for 15 minutes.
4. Aseptically add 11.1 mL of a 10% filter sterilized solution of sodium pyruvate.
5. After four hours of incubation at 30 ± 2°C, aseptically add 0.455 mL of a 0.5% aqueous solution of
acriflavin, 1.8 mL of a 0.5% aqueous solution of nalidixic acid, and 1.15 mL of a 1.0% solution ofcycloheximide in 40% ethanol to 225 mL of medium containing 25 g of sample.
Quality Control Specifications
Powder is homogeneous, free flowing, and yellow to tan.
Prepared medium is yellow with a green tint.
Expected Cultural Response:
Cultural response in Buffered Listeria Enrichment Broth Base, supplemented
with selective agents after 4 hours of incubation at 30°C, and incubated an additional 20 - 44 hours.
The organisms listed are the minimum that should be used for quality control testing.
Use recommended laboratory procedures for isolating Listeria
in food samples.
Refer to appropriate references and procedures for results.
Store sealed bottle containing the dehydrated medium at 2 - 30°C. Once opened and recapped, place
container in a low humidity environment at the same storage temperature. Protect from moisture and light by
keeping container tightly closed.
Refer to expiration date stamped on container. The dehydrated medium should be discarded if not free
flowing, or if appearance has changed from original color. Expiry applies to medium in its intact container
when stored as directed.
Limitation of the Procedure
Due to nutritional variation, some strains may be encountered that grow poorly or fail to grow on this medium.
Buffered Listeria Enrichment Broth Base
Code No. 7675A 500 g
7675B 2 kg
7675C 10 kg
Murray, E. G. D., R. A. Webb, and M. B. R. Swann.
1926. A disease of rabbits characterized by large mononuclear leucocytosis caused by ahitherto
undescribed bacillus Bacterium monocytogenes
. J. Path. Bact. 29:
Monk, J. D., R. S. Clavero, L. R. Beuchat, M. P. Doyle, and R. E. Brackett.
1994. Irradiation inactivation of Listeria monocytogenes
in low and high fat, frozen refrigerated ground beef. J. Food Prot. 57:
Bremer, P.J., and C. M. Osborne.
1995. Thermal-death times of Listeria monocytogenes
in green shell mussels prepared for hot smoking. J. Food
Grau, F. H., and P. B. Vanderlinde.
1992. Occurrence, numbers, and growth of Listeria monocytogenes
on some vacuum-packaged processed meats.
J. Food Prot. 55:
Lovette, J., D. W. Frances, and J. M. Hunt.
1987. Listeria monocytogenes
In raw milk: detection, incidence and pathogenicity. J. Food Prot. 50:
U.S. Food and Drug Administration.
1995. Bacteriological analytical manual, 8th ed., AOAC International, Gaithersburg, MD.
Contact Acumedia Manufacturers, Inc. for Technical Service or questions involving dehydrated culture media preparation or performance at (410)780-5120 or
fax us at (410)780-5470.
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