Actinobacillus lignieresi: a study of the organism and its association with its hosts

A survey of the literature lias shown that Actinobacillus lirenieresi has not been well characterised, its identification being dependent, in part, upon its association with typical actinomycotic lesions. Because of this, the existence of the commensal form of the organism has been suspected but never proven,

The morphological, cultural and biochemical characters of 220 strains of A, lignieresi isolated from pathological material have been investigated, A distinctive feature was the production of granules which, in conjunction with the bacilli themselves, gave a characteristic arrangement which has been named the "Morse code" form. A number of fermentable substrates were constantly fermented and others were consistently not attacked, whilst several substrates gave varying results with different strains. Several biochemical tests which have been shown to give constantly negative or positive results, can also be used for identification. An hitherto unrecorded character of A, lignieresi that has been demonstrated is the ability of many strains to synthesise starch from dextrose and maltose.

Th.e antigenic structure of 218 strains of A. lignieresi was investigated by slide and tube agglutination tests and absorption tests. Six antigenic types (no. 1-6) and two subtypes (la, 4a) of organisms were distinguished by differences in their heat-stable antigens; 203 of the strains were classified in these types and 15 were untyped. The majority of strains isolated from cattle belonged to type 1 and most of those from sheep to types 2, 3 and 4.

Heat labile antigens common to different antigenic types were found in living and formaldehyde-killed organisms. These antigens may be responsible for inagglutinability of living organisms tested with antisera to the heat-stable antigens. The heat-labile antigenic material appeared to be associated with extracellular slime produced in small amounts by the organism.

A medium containing oleandomycin and nystatin has been developed for the isolation of actinobacilli from mixed bacterial populations. Its use resulted in the isolation of organisms resembling A. lignieresi in morphological and biochemical characters from the ruminal contents of normal cattle and sheep and from the tongues of normal cattle. The organisms from normal animals showed an antigenic relationship with the pathogenic strains.

Antibodies to A. lignieresi have been demonstrated in sera from normal adult cattle in titres up to 1 in l60. Very young calves, however, were shown not to possess such antibodies but to acquire them gradually during their first year of life. Antibodies to A. lignieresi in the sera from normal sheep were found at slightly higher levels than in cattle.

The value of the agglutination test as a diagnostic procedure for clinical actinobacillosis has been investigated. Most sera from clinically affected cattle and from slaughterhouse cases of the disease showed higher levels of antibody than normal animals and the occurrence of a prozone in tests with such samples was a notable feature which was absent in tests with sera from normal animals.

The relationship of Bacterium equirulis (Actinobacillus equuli) to A, lignieresi has been investigated. Similarities were apparent in the morphological, cultural, biochemical and antigenic characters•