Figure Gram stain of Nocardia asteroides. Note the branching filamentous bacteria that may terminate in a rod and coccus shape. Image courtesy of US Centers for Disease Control and Prevention
Actinomyces spp and Nocardia spp are members of class Actinobacteria, which can cause opportunistic infections in dogs, cats, and other species. Both can cause pyogranulomatous or suppurative disease that is often slowly progressing and challenging to diagnose; however, some differences in organism and characteristics exist (Table 1). The incidence of disease caused by either is undefined and likely low.