One particular species, P. acnes , is a usually harmless microbe that has pathogenic potential. It has been linked to certain cases of endocarditis, wound infections, and abscesses. Ironically, it can infect acne sites on the skin but it does not cause them. Under the microscope, Propionibacterium clump up and may show a slight tendency to branch. Also, they show uneven staining patterns following a Gram-stain procedure.
Colonies grow best in an anaerobic or microaerophilic environment using blood agar.