Five strains of acid-fast bacilli isolated from nonvisiblelesion reactors were examined for biochemical characters and pathogenicity for experimental animals.
Of them, two strains isolated from imported cattle which had given positive johnin test, showing no lesions characteristic of Johns'e disease at autopsy, were identified as
Mycobacetrium avium. One nonphotochromogenic and two scotochromogenic strains isolated from non-visible-lesion reactors to tuberculin test induced macroscopic lesios of varying deg rees in the omentum, liver, and spleen, and at the site of inoculation (abdomen) when infective doses of 10
6-10
7 viable units had been injected intraperitoneally into guinea pigs. These infected animals gave positive tuberculin tests carried out with a 50-fold dilution of tuberculin. A stronger reaction to mammalian tuberculin than to avian tuverculin was observed in guinea pigs infected with the two scotochromogenic. strains A reverse relationship was obtained from guinea pigs infected with the nonphotochromogenic strain, which was identified as
M. avium.
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