Activity of bronopol (Pyceze®) against bacteria cultured from eggs of halibut, Hippoglossus hippoglossus and cod, Gadus morhua

Bronopol (2-bromo-2-nitro-1,3 propanediol) is a broad spectrum bactericide that is the active ingredient of Pyceze®. To assess the potential of Pyceze® for use in marine fish hatcheries we have determined the Minimum Inhibitory Concentration (MIC) of bronopol for 13 bacteria isolated from eggs of halibut (Hippoglossus hippoglossus) and Atlantic cod (Gadus morhua), and Escherichia coli, Staphylococcus aureus and Vibrio anguillarum as control bacteria. Six Vibrio and Moritella spp. had MIC ranging from 1–2 to 8 μg ml− 1 bronopol (mean MIC approximately 3 μg ml− 1), but other bacteria tested (Tenacibacter ovolyticus, Pseudomonas sp., Pseudoalteromonas spp., Colwellia sp., Photobacterium phosphoreum and a Cytophaga/Flexibacter sp.) were more resistant with MIC in the range 8–16 to 32–64 (mean MIC approximately 25 μg ml− 1). E. coli and S. aureus both had MIC of 32 μg ml− 1. Although the MIC of bronopol for T. ovolyticus was 16–32 μg ml− 1, a concentration of 100 μg ml− 1 bronopol had no detectable killing effect on this organism within 1 h but at 200 μg ml− 1 bronopol 90% of T. ovolyticus were killed within 30 min and > 99.99% within 2 h.