ACTINOMYCETES

A General Introduction has been added to each disease chapter in an attempt to give a brief updated overview of the taxonomic, biological and other characteristics of the virus family or group of bacteria /protozoa that cause disease in livestock and, where relevant, involve wildlife. As the text of the three-volume book Infectious Diseases of Livestock is currently under revision the Editors are aware that there are inconsistencies between the updated introductions to chapters and the content of the chapters themselves. Once the chapters have been updated – a process that is currently underway – these inconsistencies will be removed.

The classification of the bacteria collectively known as actinomycetes (based on the presence of microscopic hyphae when grown on agar, the presence or absence of spores, and the morphology of their sporangia) is complex and in flux. The genera include several of veterinary importance and may be categorized supragenerically into groups (actinobacteria, nocardio-forms, actinoplanetes, thermomonospores, maduromycetes, streptomycetes, and those with multilocular sporangia), some of which may be very heterogenous. The bacteria in the suprageneric groups have also been classified as irregular, non-sporing, Gram-negative rods (genus Actinomyces); nocardio-form actinomycetes (genera Nocardia and Rhodococcus); and as actinomycetes with multilocular sporangia (genus Dermatophilus).¹

A classification system based solely on 16s rDNA/rRNA clustering and signature nucleotides has been proposed.⁷ This divides the proposed class Actinobacteria into sixteen orders, one of which is the order Actinomycetales. Actinomycetales is divided into 5 genera, of which three are of veterinary interest. They are the genera Actinomyces, Arcanobacterium and Actinobaculum.² Other orders are Micrococcales which contains the genus Dermatophilus; and the order Corynebacteriales which contains the genera Corynebacterium, Mycobacterium, Nocardia and Rhodococcus.

Members of the genus Actinomyces, including A. bovis, and Trueperella, as T. (Corynebacterium) pyogenes is now known as Trueperella pyogenes,⁶ characteristically cause suppurative infections in tissues and organs. The disease caused by T. pyogenes is more suppurative and has a tendency to abscess formation, while that caused by A. bovis is usually characterized by a progressive, chronic, pyogranulomatous inflammatory process, the disease referred to as lumpy jaw being the best example.

Actinobaculum suis (previously known as Corynebacterium suis, Eubacterium suis and Actinomyces suis) causes cystitis, pyelonephritis and metritis in sows.^{2, 5}

The common characteristic of the nocardio-form actinomycetes is that they share the morphological complexity of the actinomycetes, and exist as fungacious mycelia that break up into rod-shaped or coccoid elements. The organisms grouped as nocardio-forms are mostly unrelated, although in certain respects some of the genera are related to the mycobacteria and corynebacteria. The two genera of veterinary importance regarded as nocardio-forms are Nocardia and Rhodococcus. The diseases caused by them are ubiquitous but usually occur sporadically, and are characterized by subacute to chronic suppurative processes which often become pyogranulomatous. Nocardia (principally N. asteroides, but also N. otitidiscaviarium, and N. brasiliensis) are associated with a variety of non-specific infections which have no species specificity nor specific site of predilection in the body. Rhodococcus equi is mostly associated with disease syndromes in foals characterized by multifocal, caseonecrotic bronchopneumonia, ulcerative enterocolitis and mesenteric lymphadenitis, and occasionally with the development of abscesses, arthritis or abortion in horses, or abscesses and other suppurative processes in sheep, goats and pigs.³

The genus Dermatophilus is morphologically characterized by being composed of filaments that break up into long, multilocular sporangia. Infection by D. congolensis is responsible for the production, principally in tropical and subtropical climates, of a superficial dermatitis in several animal species, chiefly cattle, sheep and horses. In cattle it causes Senkobo disease, which may have profound economic effects, and in sheep, lumpy wool and strawberry footrot.⁴

References

1. GOODFELLOW, M. KAMPHER, P., BUSSE, H-J., TRUJILLO, M. E., SUZUKI, K-I., LUDWIG, W. & WHITMAN, W. B., (eds). Bergey’s Manual of Systematic Bacteriology Second Edition, Volume 5 Part A. New York, Dordrecht, Heidelberg, London: Springer.
2. LAWSON, P.A., FALSEN, E., ÅKERVALL, E., VANDAMME, P. & COLLINS, M.D., 1997. Characterization of some Actinomyces-like isolates from human clinical specimens: Reclassification of Actinomyces suis (Soltys and Spratling) as Actinobaculum suis comb. nov. and description of Actinobaculum schaalii sp. nov. International Journal of Systematic Bacteriology, 47, 899–903.
3. LECHEVALIER, H.A., 1989. Nocardio-form actinomycetes. In: williams, s.t., sharpe, m.e. & holt, j.g., (eds). Bergey’s Manual of Systematic Bacteriology. Vol. VI. Baltimore: Williams & Wilkens.
4. LECHEVALIER, M.P., 1989. Actinomycetes with multilocular sporangia. In:williams, s.t., sharpe, m.e. & holt, j.g., (eds). Bergey’s Manual of Systematic Bacteriology. Vol. VI. Baltimore: Williams & Wilkens.
5. LUDWIG, W., KIRCHHOF, G., WEIZENEGGER, M. & WEISS, N., 1992. Phylogenetic evidence for the transfer of Eubacterium suis to...