Bacilli

Taxobox


image_width = 220px
image_caption = "Bacillus subtilis", Gram stained
name = Bacilli
regnum = Bacteria
phylum = Firmicutes
classis = Bacilli
subdivision_ranks = Orders
subdivision =
Bacillales
Lactobacillales

Bacilli specifically refers to a taxonomic class of bacteria. It includes two orders, Bacillales and Lactobacillales, which contain several well-known pathogens like "Bacillus anthracis" (the cause of anthrax. All members of class Bacilli are gram-positive.

Ambiguity

There are several related concepts that make use of similar words, and the ambiguity can create considerable confusion. The term "Bacillus" (capitalized and italicized) is also the name of a genus that, among many other genera, falls within the class Bacilli.

Also, "bacillus" (or the plural "bacilli") can be a generic term to describe the morphology of any rod-shaped bacterium. This general term does not mean that the subject is a member of class Bacilli or genus Bacillus. Thus, it does not necessarily imply a similar group of characteristics. Not all members of class Bacilli are rod-shaped ("Staphylococcus" is spherical), and many other rod-shaped bacteria exist that do not fall within that class ("Clostridium" is rod-shaped but very different taxonomically). Moreover, the general term "bacillus" does not necessarily indicate the Gram-positive staining common to class Bacilli. For example "E. coli" is a rod-shaped bacterium that could therefore be described as "a bacillus", but it stains Gram-negative and does not belong to genus Bacillus or class Bacilli. Some microbiologists have forsaken the general "bacillus" term because of the confusion it can create. It reproduces by binary fission. This means the cell copies its DNA and then splits itself into two identical daughter cells.