A Grammatical Dictionary of Botanical Latin

-bacter,-ris (s.m.III), ‘rod;’ (such a), or (specified) rod; bacterium.

NOTE: “Names ending in -er, including those words ending in bacter,from the Greek baktron, a rod or staff, following the special Latin rule that plant names of the third declension ending in -er are neuter (G. P. Van Eseltine 1933 THE GENDER OF GENERIC NAMES OF BACTERIA. Journal of Bacteriology . 1933 Dec;26(6):569-71.

doi: 10.1128/jb.26.6.569-571.1933.

NOTE: however this generality appears to apply only to those nouns in Latin that end in –er,-eris, and which are neuter in gender (Acer,-eris (s.n.III), Papaver,-eris (s.n.III), tuber,-eris (s.n.III)). Nouns in Greek that end in –Er, gen.sg. –eros or –Eros are masculine, and the best example is astEr, gen.sg. asteros (s.m.III); also charactEr,-Eros (s.m.III); elatEr,-Eros (s.m.III), ‘a driver).

Since –bacter is associated with the stems of various Gk. nouns, such as baktron (bactron; bactrum (s.n.II), it is assumed that –bacter would be associated with a Gk. noun such as –baktEr, with a gen.sg. –bakteros or –baktEros on analogy with other Gk. nouns with that ending, such as astEr (aster). There is actually no Greek noun or noun suffix baktEr (bacter).

Judicial Commission. 1951. The gender to be assigned to names of bacterial genera which end in –bacter. Preliminary statement no. 3 International Bulletin of Bacteriological Nomenclature and Taxonomy 1: 32—35.

It should be noted that ‘Opinion 3’ in Appendix 5 of the Bacteriological Code, 1990 Revision indicated that the “names of bacterial genera which end in –bacter should be regarded as having the masculine gender.”

-bacter,-ris (s.m.III), ‘rod.’

      singular         plural         singular          plural
Nom.  bacter      bacteres     Arcobacter    Arobacteres
Gen.   bacteris    bacterum    Arcobacteris  Arcobacterum
Dat.   bacteri     bacteribus   Arcobacteri    Arcobacteribus
Acc.   bacterem  bactera      Arcobacterem Arcobacteres
Abl.    bactere    bacteribus   Arcobactere   Arcobacteribus

Acinetobacter,-eris (s.m.III); Aerobacter,-eris (s.n.III);

Campylobacter,-eris (s.m.III) ‘curved rod’ (Bacterium);

NOTE: C. helveticus .

Citrobacter,-eris (s.m.III); ‘citrate-utilizing rod’ (bacterium).

NOTE: C. amalonaticus and C. europaeus have masc. endings.

Dichelobacter,-eris (s.m.III);

NOTE: D. nodosus has a masc. ending (one species in the genus).

Enterobacter,-eris (s.m.III);

NOTE: the A-adjectives in the epithets of this genus are all masculine.

Helicobacter,-eris (s.m.III); ‘helix-shaped rod’ (bacterium).

NOTE: H. typhlonicus, masculine ending. Nitrobacter,-eris (s.m.III), a nitrite-oxidizing or nitrifying bacterium.

NOTE: this genus also has a masculine adj. N. alkalicus.