Loss of Polymyxin B From Enrichment Broth for Vibrio parahaemolyticus

Polymyxin B sulfate (PB) added to salt broth (SB) for selective enrichment of Vibrio parahaemolyticus was destroyed by autoclaving. Losses were about 49% at pH 7.4 and 97% at pH 8.8. Additionally, certain raw fish when added to salt polymyxin broth (SPB) caused a loss of PB, probably due to adsorption; vertebrate fish (red snapper and herring) caused a loss of about 72% of PB, but shellfish (oyster and clam) did not cause any loss.