The order of actinomycetales comprises a number of different human pathogens, including the families actinomycetaceae, nocardiaceae and mycobacteriaceae. Mycobacterial diseases have been presented in Chapters 11 and 15. Diseases due to Nocardia spp. are described in the second part of this chapter. The aerobic actinomycetes such as Actinomadura madurale and Streptomyces somalienses produce progressive destructive infections usually in peripheral soft tissues called madura foot.

This chapter will describe respiratory infections due to Actinomyces spp. producing actimycosis and pulmonary infections due to Nocardia spp.

Actinomyces spp. and actinomycosis

Bacteriology, immunopathogenesis and epidemiology

The actinomycetaceae family has a variable tendency to form filaments as a result of failure to separate with growth. The higher actinomycetes are characterised by extensive branching filaments which may project above the colony (aerial forms). These appearances are termed hyphae/mycelia and the ray-like appearances of the sulphur granules of Actinomyces israelii led to previously erroneous classification as fungi. Actinomyces means ray fungus. However, lack of sporulation, budding, absence of chitin and glucan in the cell wall, lack of a nuclear membrane, non-response of infections to antifungal agents, replication by bacterial fission and response to penicillin/tetracycline reclassified them as higher bacteria.

The organism responsible for actinomycosis was recognised when the disease ‘lumpy jaw’ in cattle was described, and was named Actinomyces bovis by Bollinger. The organism does not produce human disease.