Minimum growth temperatures and those of decreased growth were determined for 100 strains of listerias. The ability of 78 strains of Listeria monocytogenes isolated from animals and 22 non-haemolytic strains to grow at low temperatures was studied, using a flooding technique, in a plate-type continuous temperature gradient incubator at temperatures between -1.6 and 14.5 degrees C. The mean minimum temperature for L. monocytogenes was +1.7 +/- 0.5 degrees C. The growth of non-haemolytic listerias was unobservable at +1.7 +/- 0.5 degrees C. The L. monocytogenes strains grew at about 0.6 degrees C lower than the non-pathogenic strains. No differences in growth temperatures were observed among L. monocytogenes strains isolated from different sources. The serovars with the OI antigen grew at lower temperatures (+1.0 +/- 0.3 degrees C) than the other common serovar 4b (+1.3 +/- 0.4 degrees C). The results indicate that L. monocytogenes grows better than non-haemolytic strains under cold conditions. The possible role of haemolysins as growth factors is also discussed.

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The fate of L. monocytogenes during the fermentation of Finnish fermented sausage was examined. L. monocytogenes was able to survive during a 21 d fermentation of sausage with levels of nitrite and salt commonly used in the meat industry today (120 ppm NaNO2 and 3.0% NaCl). Initial numbers of Listeria (103 CFU/g and 105 CFU/g) decreased approximately 1 log 10 CFU/g during the manufacture. Increasing the levels of nitrite/nitrate to those used 30 years ago in meat products had a marked effect on the elimination of Listeria. The numbers of survivors in the sausages was reduced 2.0 log 10 CFU/g during the fermentation of 3 weeks with a combination of 200 ppm NaNO2 and 300 ppm KNO3. With 1000 ppm KNO3, the decrease was 3.3 log 10 CFU/g. L. monocytogenes could not be totally eliminated from highly contaminated sausage by increasing only the levels of nitrite and nitrate. Levels of these additives with best bacteriostatic effect on Listeria are no longer permitted in food.

Listeria monocytogenes septicemia in an 80-year-old man is described. On the day before clinical symptoms appeared the patient had eaten homemade salted mushrooms, rufous milkcap (Lactarius rufus Fr.). L. monocytogenes serotype 4b was isolated in blood cultures. The mushrooms which had been stored in cold for 5 months before consumption contained the same listeria serotype at a level of 10(6) CFU/g. Salt content (NaCl) of the mushrooms was 7.5%. Fever and diarrhea disappeared with penicillin therapy and the patient was discharged after 4 weeks in the hospital.

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