Candling Egg in Microbiology: Introduction and Its Applications

Candling egg

 Introduction of Candling egg

Candling egg simple means to check an egg in the presence of candlelight light. It is useful in microbiology.

Applications of Candling egg 

The candling of eggs in microbiology is very important for the following purposes.

  • As you know certain bacteria like Chlamydia and viruses are not able to grow on inanimate (artificial) media, therefore in such conditions egg inoculation is the choice of cultivation for those organisms as a form of animate medium, and before inoculation, there is a need of candling of egg to check the various routes of egg inoculation.
  • Candling of an egg is used to check the viability of an embryonated egg.
  • Similarly, it also uses to check the position of the embryo.

Embryonated Egg Inoculation

Goodpasture  (1931) first used embryonated hen eggs for the cultivation of viruses. Embryonated hen egg (7-12 days old) is inoculated by one of the several routes such as chorioallantoic membrane, allantoic cavity, amniotic sac, and yolk sac. After inoculation, eggs are incubated for 2 to 9 days.

Chorioallantoic Membrane (CAM)

It is inoculated mainly for growing poxviruses. It produces visible lesions (pocks). Each pock is derived from a single virion. Pock counting, therefore, indicates the number of viruses present in the inoculum. Pocks produced by different viruses have different morphology.

Allantoic cavity

Allantoic inoculation is employed for growing the influenza virus for vaccine production. Other chick embryo vaccines include yellow fever and rabies vaccines. Duck eggs being bigger, provide a better yield of rabies virus and were used for the preparation of the inactivated non-neural rabies vaccine.

Amniotic sac

Inoculation into the amniotic sac is mainly used for the primary isolation of the influenza virus.

Yolk sac inoculation

It is inoculated for the cultivation of some viruses and certain bacteria i.e. chlamydia and rickettsiae.


  1.  Fields Virology Vol I & II, Editor in Chief: David M. Knipe & Peter M. Howley,  Asso editors: Diane E. Griffin, Robert A. Lamb, Malcolm A. Martin, Bernard Roizman & Stephen E. Straus, 5th ed 2007, Publisher Lippincott Williams & Wilkins, Wolters Kluwer Health, USA
  2. Topley & Wilsons Principle of  Virology  Editors: M.T. Parker & L.H. Collier, 8th ed 1990, Publisher Edward Arnold publication, London.
  3. Bailey and Scott’s  Diagnostic Microbiology -13th Edn.
  4.  Mackie & Mc Cartney  Practical Medical Microbiology- 14th  Edn.
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