DNA fingerprinting of Mycobacterium bovis strains by restriction fragment analysis and hybridization with insertion elements IS1081 and IS6110.

Strains of Mycobacterium bovis, the causative organism of bovine tuberculosis, can be clearly distinguished from each other by restriction fragment analysis. This method of DNA fingerprinting has been used for many epidemiological studies in New Zealand, but the technique presents practical difficulties that hinder its widespread use. The insertion element IS6110 is being widely used as a DNA probe for distinguishing restriction fragment polymorphisms among strains of Mycobacterium tuberculosis. Both this element and another recently sequenced element, IS1081, are also present in M. bovis. We assessed the usefulness of these two elements for distinguishing between 160 strains of M. bovis. These strains, most of which were isolated in New Zealand, were selected to be representative of the 95 different types that were identified among 530 strains that were previously typed by restriction fragment analysis. Fifteen IS6110 types were identified, but more than half of the strains representing 46 restriction types had the same IS6110 type. Virtually all M. bovis strains as well as strains of M. tuberculosis and Mycobacterium africanum had the same IS1081 type. The results indicate that for M. bovis, IS1081 cannot be used to type strains, IS6110 can be used to distinguish strains into broad groups, but only restriction fragment analysis is sufficiently sensitive for detailed epidemiological studies. An investigation of the host range of IS1081 revealed that, apart from its presence in species of the tuberculosis complex, it is also present in a strain of Mycobacterium xenopi.

Duration of resistance to experimental footrot infection in Romney and Merino sheep vaccinated with Bacteroides nodosus oil adjuvant vaccine.

Groups of 10-12 Romney and Merino wethers were challenged simultaneously with homologous experimental footrot infection after having received the second of 2 doses of Bacteroides nodosus (strain 198) vaccine 0, 4, 8, 12, 16 and 20 weeks previously. Inoculations were carried out 28 days apart and unvaccinated sheep of both breeds were challenged as controls. Most Romneys that had been vaccinated up to 16 weeks prior to challenge were resistant to footrot whereas 8 of 10 controls were susceptible. This resistance was lost by about 20 weeks after vaccination. By contrast, protection against challenge in vaccinated Merinos lasted only about 4-5 weeks, although residual benefits of vaccination were apparent after longer intervals from the reduced number and severity of foot lesions among vaccinates compared with controls. Agglutinin titres, which did not differ markedly after similar intervals between Romneys and Merinos, reached maximum levels between 4 and 8 weeks after the second vaccine dose and subsequently declined. Although peak titres were generally recorded at the time of maximum protection in Merinos, the relationship between agglutinin levels and resistance in the Romneys was ill-defined.

Differentiation of Bacteroides nodosus biotypes and colony variants in relation to their virulence and immunoprotective properties in sheep.

To obtain a wider definition of variation in the virulence of Bacteroides nodosus and in the protective potency of B. nodosus vaccines, we made a comparison of the in vitro characteristics of isolates from clinical infections of sheep and cattle and of certain colony variants observed previously. Three basic colony types were distinguished: papillate or beaded (B)-type colonies were produced by fresh isolates from advanced ovine foot rot; mucoid (M)-type colonies were formed by isolates from noninvasive B. nodosus infections of the interdigital skin of sheep and cattle, and also by cultures of some primary B-type colonies passaged nonselectively in vitro; and circular (C)-type colonies were formed by B. nodosus that eventually predominated in repeatedly passaged liquid subcultures. Each type could be maintained by selective agar subculturing; one strain was thus passaged 40 times as the B-type colony, at which point the organisms induced severe foot rot in experimentally infected sheep. Cultures of M-type colonies were uniformly less pathogenic and those of C-type colony organisms were avirulent. In vitro changes from prototype B-type colonies to M- and C-variants were nonreversible in these experiments, were accelerated in liquid cultures, and wee accompanied by a diminution in elastase activity of the organisms and in their immunoprotective properties against homologous challenge. Strains differed in their stability to these changes; therefore the choice of an appropriate strain and colony type may be an important consideration in studies of B. nodosus virulence and in the development of effective vaccines.