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Egg Yolk Agar (EYA)

Egg Yolk Agar (EYA) is an enriched non-selective and differential medium for the presumptive identification of certain anaerobic isolates. Egg Yolk Agar medium contains a suspension of egg yolk for the presumptive identification of various Clostridium, Fusobacterium and Prevotella spp. The egg yolk suspension allows for the detection of lecithinase and lipase activity. The degradation of lecithin in the egg yolk results in an opaque precipitate around the colonies.  The Lipase enzyme hydrolyzes the fats within the egg yolk, which results in an iridescent sheen on the colony surface.  Another common reaction observed is proteolysis of the egg yolk as indicated by a clearing of the medium around the colonies.  This medium  is supplemented with vitamin K1 and Hemin to facilitate the recovery of anaerobes.  This medium is dispensed under oxygen-free conditions to prevent the formation of oxidized products prior to use.

           Anaerobe Systems PRAS Egg Yolk Agar (EYA) AS-511

Egg Yolk Agar Products

 Item #





 EYA mono plate

 1 plate



Pancreatic Digest of Casein, 20.0 g

Yeast Extract, 5.0 g

Pyruvate, 0.5 g

Sodium Chloride, 2.5 g

Dextrose, 2.0 g

L-Tryptophan, 0.2 g

Tween 80, 1.0 ml

Hemin (0.1% soln), 5.0 ml

Vitamin K1 (1% soln), 1.0 ml

L-Cystine, 0.4 g

Sodium Phosphate, 5.0 g

Magnesium sulfate (5% soln), 0.2 ml

Agar, 20.0 g

Egg Yolk Suspension, 100.0 ml

Distilled Water, 1000.0 ml


Final pH 7.1 +/- 0.2 at 25 degrees C.

Final weight 16.0 g +/- 1.6. 


For IN VITRO DIAGNOSTIC USE only.  Approved biohazard precautions and aseptic techniques should be observed when using this product.  This product is for use only by properly-trained and qualified personnel.  Sterilize all biohazard waste prior to disposal.

Storage and Shelf Life

Storage:  Upon receipt, store at room temperature (13°C - 27°C) in original container until use.  Avoid overheating or freezing.  Do not use medium if there are signs of deterioration (shrinking, cracking or discoloration) or contamination.  The expiration date applies to the product in its original packaging and stored as directed.  Do not use product past the expiration date shown on the container.

Shelf Life:  90 days from date of manufacture.


Specimen Collection:  Specimens for anaerobic culture should be protected from air (oxygen) during collection, transport and processing.  Consult appropriate references for detailed instructions concerning collection and transport of anaerobes. 

Methods for Use:  Egg Yolk Agar should be inoculated with a pure culture of an isolate for the detection of lipase and/or lecithinase.  Inoculated plates should be streaked to obtain isolated colonies, immediately place plates in an anaerobic atmosphere and incubated at 35-37oC for 18-48 hours.  Additional periods of incubation may be necessary to recover some anaerobes.  Detailed instructions for processing anaerobic cultures can be found in the appropriate references.

Materials Required But Not Provided

Standard microbiological supplies and equipment; such as loops, saline blanks, slides, staining supplies, microscope, incinerator / autoclave, incubators, anaerobic chamber or anaerobic jars, other culture media and serological and biochemical reagents. 


Egg Yolk Agar will not provide complete information for identification of bacterial isolates.  Additional test procedures and media are required for complete identification.  Consult reference materials for additional information.

Quality Control

Egg Yolk Agar should support good growth of obligate anaerobes found in clinical infections.  In addition, this medium should support typical lecithinase reaction produced by some Clostridia species and a lipase reaction produced by some Fusobacterium and some Clostridia species. 

The following organisms are routinely used for quality assurance testing at Anaerobe Systems. 

Organism Tested


Time (Hours)

Special Reaction

Bacteroides fragilis (ATCC 25285)


24 h


Prevotella melaninogenica (ATCC 25845)


24 – 48 h


Fusobacterium necrophorum (ATCC 28286)


24 h

Lipase reaction

Fusobacterium nucleatum (ATCC 25586)


24 h


Clostridium perfringens (ATCC 13124)


24 h

Lecithinase reaction

Peptostreptococcus anaerobius (ATCC 27337)


24 h


Staphylococcus aureus (ATCC 25923)


24 h


Propionibacterium acnes (ATCC 6919)


24 – 48 h


Clostridium difficile (ATCC 9689)


24 h



User Quality Control: The final determination to the extent and quantity of user laboratory quality control must be determined by the end user.

If sterility testing is to be performed on this product, the appropriate percentage of the original shipment amount should be incubated anaerobically and aerobically for 48 – 96 hours.

If the nutritive capacity of this medium is to be tested for performance, it is recommended that the following ATCC organisms be evaluated for growth.




Special Reaction





B. fragilis

24 hrs



F. necrophorum

48 hrs



C. perfringens

24 hrs



C. difficile

24 hrs




Physical Appearance:  Egg Yolk Agar should appear opaque and yellow in color.



1.        Dowell, V. R., Jr. and T. M. Hawkins.  1974.  Laboratory Methods in Anaerobic Bacteriology.  CDC Laboratory Manual.  USDHEW C. D. C. Atlanta, GA 30333.


2.        Dowell, V. R., Jr. and G. L. Lombard.  1977.  Presumptive Identification of Anaerobic Non-sporeforming Gram-negative Bacilli.  USDHEW, CDC.  Atlanta, GA 30333.


3.        Dowell, V. R., Jr., G. L. Lombard, F. S. Thompson and A. Y. Armfiedl.  1977.  Media for the Isolation, Characterization, and Identification of Obligately Anaerobic Bacteria.  USDHEW, CDC, Atlanta, GA 30333.


4.        Holdeman, L. V., F. P. Cato and W. E. C. Moore.  1977.  Anaerobe Laboratory Manual.  Virginia Polytechnic Institute and State University.  Blacksburg, VA 24061.


5.        Jousimies-Somer, H. R., Summanen, P., Citron, D. M., Baron, E. J., Wexler, H. M. and S. M. Finegold.  2002.  Wadsworth – KTL Anaerobic Bacteriology Manual.  Star Publishing Co.  Belmont, CA 94002.


6.        NCCLS.  Quality Control for Commercially Prepared Microbiological Culture Media; Approved Standard- Third Edition.  (2004).  NCCLS document M22-A3.  NCCLS, 940 West Valley Road, Suite 1400, Wayne, PA 19087-1898.