IRREGULAR, NON-SPORING, GRAM-POSITIVE RODS

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 bacteria in this group include a wide collection of ‘diphtheroids’ (i.e. non-sporeforming, non-motile, nonencapsulated, pleomorphic, irregularly staining, Gram positive bacterial rods occurring in angular or palisade arrangements), previously classified as Corynebacterium spp. (‘coryne’ [Greek] = club).

Recent taxonomic revision by means of thin layer chromatographic analysis of whole organism methanolysates, as well as by means of 16S rRNA gene sequence analysis, has resulted in the reclassification of some bacteria that were previously assigned to the genus Corynebacterium. There are currently over 80 members of Corynebacterium group, and the relevant species, in the genus Corynebacterium are C. pseudotuberculosis (formerly C. ovis), the C. renale group and C. bovis.¹ Corynebacterium (Actinomyces) pyogenes, C. (Eubacterium) suis and C. equi have been relocated in the genera Trueperella pyogenes,¹⁰ Actinobaculum⁶ and Rhodococcus³ respectively. In the most recent edition of Bergey’s Manual of Systematic Bacteriology  (new Goodfellow, 2012), Corynebacterium, Actinomyces and Trueperella are  grouped in the family Actinomycetaceae, while Rhodococcus is in the family Nocardiaceae (see Rhodococcus equi infections).

True Corynebacterium spp. are characterized by the presence of arabinose, galactose, meso-diaminopimelic acid (meso-DAP) and peptidoglycan in the cell wall, and corynomycolic acids of chain length between 22 and 36 carbon atoms.^{1, 8}

Although Rhodococcus spp. also contain arabinose, galactose and meso-DAP in their cell walls, they differ in having tuberculostearic acids and 32 to 66 carbon mycolic acids.³ Bacteria in the genera Actinomyces and Trueperella contain L-lysine but not meso-DAP nor arabinose in their cell walls,⁸ while rhamnose is the major sugar component of the cell wall of Actinobaculum suis.⁷

In southern Africa, Corynebacterium pseudotuberculosis and Trueperella pyogenes are the most important bacteria of the genera considered here. Of these two species, ⁷² per cent of isolations made at the Onderstepoort Veterinary Institute in South Africa between 1980 and 1989 were Trueperella pyogenes.⁴

Bacteria from the above genera are readily isolated on blood agar media. Although the colonies and microscopic morphology are quite distinct, the various organisms are best distinguished on the basis of their biochemical characteristics, some of which are given in Table 1.^{1–3, 5–11}

Disease conditions in farm animals that are caused by the above bacteria are listed in Table 2.

Table 1 Laboratory differentiation of Corynebacterium, Actinobaculum, Actinomyces, Trueperella and Rhodococcus spp. of importance in diseases of farm animals

Table 2 Diseases caused by Corynebacterium, Actinobaculum, Actinomyces, Trueperella and Rhodococcus spp. in farm animals