Bacillus (shape)

A bacillus (plural bacilli) is a rod-shaped cylindrical bacterium.S. Srivastava; Prem S. Srivastava, Understanding Bacteria (Dordrecht; Boston; London: Kluwer Academic Publishing, 2003), p. 61 Bacilli are found in many different taxonomic groups of bacteria.

When the name Bacillus is capitalized and italicized, it  refers to a specific genus of bacteria.Paul G. Engelkirk; et al 2011. Burton's microbiology for the health sciences. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, p. 53. 

If it is not capitalized or italicized the name refers to any rod-shaped bacterium. 

There is no connection between the shape of a bacterium and its colors in the gram staining. In other words, some of them are gram negative and some are gram positive.

 References 

Category:Bacteria