Bacteriology of Indole Production in Shrimp Homogenates Held at Different Temperatures

Homogenized, head-on, white shrimp ( Penaeus setiferus ) were held at 4, 12 and 22°C until putrefactive spoilage occurred. Repetitive bacterial sampling was performed and 1647 bacterial isolations were made from the shrimp homogenates. Of these, 42 isolates (2.6%) produced indole. Isolates that produced indole belonged to the genera Flavobacterium (52.4%), Aeromonas (23.8%), Proteus (21.4%) and Yersinia (2.5%). No Escherichia coli were isolated. Aeromonas and Proteus exhibited proteolysis and were able to produce indole in shrimp extracts without added L-tryptophan. These organisms favored higher growth temperatures. The majority of the Flavobacterium isolates were psychrotrophic, non-proteolytic and could not produce indole in shrimp extracts without added L-tryptophan. Suppression of bacterial reproduction with antibacterial compounds inhibited indole production. Two paths of indole production are suggested based on temperature of decomposition.