Heat Resistance and Virulence of Serovars of the Mycobacterium a Vium Complex

Pavlas, M.: Heat Resistance and Vinllence ofSerovars of the Mycobacterium avium Complex. Acta vet. Bmo 1997,66: 249-252. Heat resistance and virulence tested in chickens were investigated in 151 strains classified with the Mycobacterium avium complex. The highest differences in heat resistance between virulent and avirulent strains were found at 2-h exposure to 60°C. Under such conditions, 92% of avirulent strains classified with Mycobacterium intracellulare serovars 4. 8, 9 (Schaeffer 1965) were resistant. On the other hand only 4.8% of virulent strains of Mycobacterium avium subsp. avium serovars 2, 3 resisted the above exposure conditions. Mycobacterium avium complex. virulence. heat resistance Species designated already in the past century as Bacillus tuberculosis gallina rum (Sternberg 1892), identical with Mycobacterium tuberculosis typus gallinaceus (Lehmann and Neumann 1896) and Mycobacterium tuberculosis avium (Chester 1901), are currently of greatest importance among pathogenic mycobacteria. Mycobacterial strains with biological properties closely resembling those of M. avium subsp. avium (hereinafter M. avium) were isolated from porcine lymph nodes in the fifties of this century. These porcine strains did not induce any lesions in rabbits even after intravenous inoculation. With regard to their origin, it was recommended to classify them as a separate species Mycobacterium suis (Baumann et al. 1955). Similar strains nonvirulent in chickens were isolated several years later from human patients suffering from a tuberculosis-like disease. Pneumokoniosis was identified as a predisposing factor in the patients. The strains were isolated at the Battey State Hospital, Georgia, and were designated Mycobacterium battey accordingly (Crow et al. 1957). The very close similarity of biochemical properties did not allow the differentiation of the above mycobacterial species. On the other hand, marked virulence of M. avium in birds and other animal species was a relatively reliable characteristic for distinguishing this species from M. intracellulare. Comparative investigations of M. avium and M. intracellulare revealed differences in surface antigens allowing, by means of agglutination test, the identification of 2 serovars of M. avium and another 15 serovars of M. intracellulare (Schaeffer 1967). So far 29 serovars of the M. avium-intracellulare complex have been identified. The serovars 1,2 and 3 were considered to belong to M. avium pathogenic for birds. According to OlE (1996), the serovar 6 of M. intracellulare ranks with potential agents inducing avian tuberculosis. There can be no doubt that serological typification of the M. avium-intracellulare complex has become an important component epidemiological investigations. Serovar 2 is apparently the most significant of them owing to its high prevalence and virulence for pOUltry, other bird species and mammals, particularly swine. Serovar 3 differs from serovars 1 and 2 in its specific lipid composition and surface antigens (M ar k s et al. 1969). Variable virulence has been reported for serovar 1 isolated frequently from human patients. The virulence of