INCIDENCE OF HISTAMINE-FORMING BACTERIA AND HISTAMINE CONTENT IN SCOMBROID FISH SPECIES FROM RETAIL MARKETS IN THE BARCELONA AREA

Incidence and diversity of histidine decarboxylating bacteria were det ermined in samples of tunafish, bonito and mackerel purchased at diffe rent retail markets. Histamine-forming bacteria occurred in a low prop ortion and always accounted for less than 0.1% of the total bacterial load in the fish samples studied. Similarly, histamine content in fish samples also was low (< 25 ppm) and all of them met current histamine standards established by the European Union. Histamine was found in 8 3.3% of the tested tunafish samples with an average of 8.9 ppm. In con trast, none of mackerel samples and only 2 out of 12 of bonito showed detectable amounts of histamine. Morganella morganii and Klebsiella ox ytoca were the most active histamine formers under experimental condit ions, and produced on average 2765 and 1415 ppm of histamine, respecti vely, after incubation at 37 degrees C for 18 h. Some new histamine fo rmers, such as Plesiomonas shigelloides, Enterobacter intermedium, Ser ratia marcescens, Serratia plymuthica and Serratia fonticola, have bee n identified. Especially Plesiomonas shigelloides would have an import ant role within histidine decarboxylating bacteria because it was the sole histamine former isolated that has frequently been associated wit h the marine aquatic environment. However, only 8-340 ppm of histamine was formed by these strains in laboratory trials.