Other organisms that can initially be mistaken for Corynebacterium include aerobic Actinomyces that may be found in the human sinus or periodontal areas and in other clinical samples. Aerotolerant Bifidobacterium and Varibaculum can also be seen on initial direct specimen Gram stains and mistaken as possible Corynebacterium species. In addition, other loosely related organisms that can be recovered from clinical samples and have been shown to cause disease include Actinomadura, Tsukamurella, Gordonia, Nocardia, and rarely Micromonospora. Some of these isolates can quickly be separated from Corynebacterium based on partially acid-fast staining, Gram stains, and colony morphology and color.
Note: Isolates that cannot be easily distinguished because they are partially acid-fast negative and have a similar Gram stain and colony color and morphology may need to be further identified using additional biochemicals or utilizing Maldi-TOF or sequencing methods.
As medicine and treatments expand and advance, previously considered "harmless" organisms may continue to find their niche and opportunities to invade and infect patients. An investigation is warranted when unusual or non-pathogenic organisms are found in pure culture or found in multiple cultures from the same source.
