VMC 311: Systematic Veterinary Bacteriology and Mycology (2+1)

PEARL-STRING TEST,ASCOLI'S TEST AND ANIMAL INOCULATION TEST

Pearl – string test

• When Bacillus anthracis is grown for 2-3 hours on solid media containing 0.05 to 0.5 IU penicillin / ml, due to impairment of cell wall, the bacilli become spherical in appearance resembling a string of pearls. This test is an adjunct to the rapid recognition of anthrax bacilli.

Ascoli’s Test

• Because of advanced autolysis, the anthrax bacilli are no longer demonstrable in the tissues, so the thermoprecipitation test of Ascoli can be applied to detect the presence of anthrax antigen.
• This method is based on the demonstration of the anthrax antigens by precipitation.

Procedure

• Boil a piece of tissue (ear piece) in 5 ml of acidified saline (with 1/1000 acetic acid) for 5 minutes.
• Filter the fluid and this will serve as the source of antigen.
• Take 0.5 ml of anthrax antiserum in a narrow tube and add 0.5 ml of the filtrate.
• Development of a distinct ring of precipitate at the interface within 15 minutes indicates positive reaction.

Animal Inoculation test

• Sub-cutaneous inoculation of suspected material into guinea pig or mouse result in death within 48 hours with lesions like gelatinous haemorrhagic oedema at the inoculation site, congested viscera, dark red blood and enlarged darkened spleen.
• Smears from splenic pulp if stained by Gram's method will reveal typical Gram positive bacilli.