Other common causative organisms include other Gram-negative aerobes, Streptococcus spp. and anaerobes.

It is mandatory that antibiotics provide coverage for Escherichia coli and other Gram-negative facultative anaerobes, and for Bacteroides spp.

The causative agent is Aeromonas salmonicida a non-motile, Gram-negative aerobic bacillus, typically 1 µm x 2 µm.

B. fragilis is a Gram negative short bacillus which demonstrates pleomorphism.

A fluorescent, Gram-negative bacterium was consistently isolated from diseased tissues onto King's B medium.