A coccobacillus (plural coccobacilli) is a type of bacterium with a shape that is intermediate between cocci (spherical bacteria) and bacilli (rod-shaped bacteria). Coccobacilli are therefore in essence very short rods which may be mistaken for cocci. Haemophilus influenzae, Gardnerella vaginalis, and Chlamydia trachomatis are coccobacilli. Aggregatibacter actinomycetemcomitans is a gram-negative coccobacillus that is prevalent in subgingival plaques. Acinetobacter strains may grow on solid media as coccobacilli. Bordetella pertussis is a gram-negative coccobacillus responsible for causing whooping cough.
Coxiella burnetti is also a coccobacillus.
Bacteria from the Brucellae genus are medically important coccobacilli that cause brucellosis.
Haemophilus ducreyi is another medically important gram-negative coccobacillus and is observed in sexually transmitted disease, chancroid, of third-world countries.