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A total of 245 strains of Listeria monocytogenes were investigated. These strains were isolated from human and animal cases of listeriosis as well as from different kinds of raw and processed foods. Thirty-three electrophoretic types (ETs) were identified among the 245 strains. The strains investigated included all human clinical strains isolated in Denmark during 1989 and 1990. Seventy-three percent of the strains isolated in this period were assigned to one of only two ETs (ET 1 and ET 4). ET 1, which was found to be the most frequently occurring ET among strains isolated from human clinical cases, was also found to occur rather frequently in animal clinical cases. ET 1 was, however, found only sporadically among strains isolated from foods and food factories. The data indicate that there might be something distinctive about the physiology or ecology of the ET

Nitrate and nitrite are used in meat and fish curing, and in the manufacture of certain cheeses. Nitrate itself has little antimicrobial effect and in most applications could be replaced by lower concentrations of nitrite. Further, improved hygiene diminishes the need for nitrite. The antimicrobial activity and technological needs for nitrate and nitrite are reviewed. It is concluded that the technological needs for nitrite in meat products stored at < 10 degrees C could be met by added nitrite concentrations of 50 mg/kg. The overall effect of nitrate in salted fish appears to be marginal. In such products, Vibrio parahaemolyticus does not grow at salt concentrations of 10% and food poisoning by this organism is not related to the absence of nitrate or nitrite; growth of Clostridium botulinum Type E (the predominant cause of botulism from fish products) is arrested by salt concentrations of 3-4%. Listeria monocytogenes in seafood cannot be controlled by nitrite. The use of nitrate in cheese production could be avoided, or at least reduced to a low level by avoiding silage with a high count of gas-producing Clostridia and hygienic milk collection.