Histamine and tyramine-forming microorganisms in Spanish traditional cheeses

Histamine and tyramine-forming micro-organisms were studied in 44 samples of different varieties of Spanish cheeses. Isolates (694) were obtained and tested for histidine and tyrosine-decarboxylase activity. Tyramine-forming activity was more frequent in the microorganisms isolated from most of the selective culture media except in those for enterobacterias and moulds. Tyramine-forming identified isolates were mostly Gram positive bacteria (enterococci and some lactic acid bacteria), whereas histamine was formed mainly by enterobacteria, but by some lactic acid bacteria as well. Most of the tyramine-forming lactic acid bacteria strains were isolated from cheeses containing the highest tyramine amounts. Some of these cheeses also showed the highest counts of enterococci. However, histamine-forming lactic acid bacteria were isolated from samples generally containing less than 100 mg/kg of histamine. The amount of tyramine found in the samples was significantly higher than histamine. One sample of Cabrales cheese (a mould-matured cheese) presented the highest amounts of both histamine (928 mg/kg) and tyramine (1807 mg/kg).