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.