| Gram Stain | |
 Small rods form clusters | |
| Catalase Test | |
| |
| Negative | |
| |
| Grey-black colonies on tellurite blood agar plate | |
| Corynebacterium diptheriae | |
| Most Corynebacterium spp. are commensal organisms, often found in the oropharyngeal region, and they may be reported as 'diptheroids' on gram stain reports. | |