Mycobacterium

Mycobacterium (myco=fungus) was named based on how they have been observed to grow like fungus on the surface of water when cultured. 
Mycobacterium tuberculosis is a pathogenic species and is the main cause of tuberculosis. Due to its extremely waxy coating, it is impossible to gram stain, making it difficult to observe the bacteria before acid-fast stains and fluorescence microscopy were introduced.