The suffix -bacter is in microbiology for many genera and is intended to mean "bacteria".
Bacter is a Neolatin term coined from bacterium, which in turn derives from the Greek βακτήριον, meaning small staff (diminutive of βακτηρία). Consequently, it formally means "rod". It differs from the suffix -bacterium in grammatical gender, the former being male and the latter being neuter, this was decided in a juridical opinion of the bacteriological code (n° 3).
Nevertheless, for historical reasons, two archaeal species finish in -bacter: Methanobrevibacter and Methanothermobacter.
The Judicial Opinion n° 2 discusses the declension of the word given that many authors assumed the genitive to be bactris (3rd decl. words of Latin origin ending in ter), bacteri (2nd decl.) or bacteris (3rd, words of Greek origin, like astris), and opts for the latter. consequently higher taxa are formed with the stem - bacter- and not -bactr-. In Juridical opinion n° 3 it was established to be masculine. For example, Campylobacter is a genus of Campylobacterales. It should be noted that these rules were established so that the specific epithets were paired with the correct gender as imposed by the Bacteriological Code and the correct higher taxa were formed. An interesting effect of this is that the genus Fibrobacter gives its name to the phylum Fibrobacteres, which obeys Latin grammar, and to the class Fibrobacteria, which follows the recommendation of using the suffix -ia