This article is about the bacterial class. For the genus, see Bacillus
. For rod-shaped bacteria in general, see bacillus (shape)
Bacilli 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).
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. All types of bacteria are one-celled organisms that live either alone, in chains, or in groups.
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 that do not fall within that class (Clostridiumkamina dalla kotta is rod-shaped but very different taxonomically) exist. 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.
The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LSPN)   and the phylogeny is based on 16S rRNA-based LTP release 106 by 'The All-Species Living Tree' Project 
♠ Strains found at the National Center for Biotechnology Information (NCBI) but not listed in the List of Prokaryotic names with Standing in Nomenclature LPSN
Bacilli part 2 (continued) 
- ^ See the List of Prokaryotic names with Standing in Nomenclature. Data extracted from J.P. Euzéby. "Bacilli". Retrieved 2012-05-17.
- ^ See the NCBI webpage on Bacilli Data extracted from Sayers et al. "NCBI Taxonomy Browser". National Center for Biotechnology Information. Retrieved 2012-05-17.
- ^ See the 'The All-Species Living Tree' Project . Data extracted from the "16S rRNA-based LTP release 106 (full tree)". Silva Comprehensive Ribosomal RNA Database. Retrieved 2012-05-17.