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Survival of Listeria monocytogenes in Low pH Model Broth Systems

Parish, Mickey E., Higgins, Dianne P.
Journal of food protection 1989 v.52 no.3 pp. 144-147
Listeria monocytogenes, blood serum, cell viability, models, pH, storage temperature, yeast extract
Four strains of Listeria monocytogenes were studied for pH tolerance in pH-adjusted tryptic soy broth supplemented with yeast extract. After incubation at 30°C, all strains grew at pH 4.5 and above. Survival of strain F5069(4b) was further investigated in sterile orange serum in which pH was adjusted from 3.6 to 5.0 in 0.2 unit increments. At 4°C, viable cells were reduced from 106 cfu/ml to less than 25 cfu/ml in 25 d at pH 3.6, 43 d at pH 4.0, and 81 d at pH 4.6. Viable cell populations remained at levels about 10(2) after 90 d in orange serum at pH 4.8 and 5.0. At 30°C, the same reductions were observed at 5 d at pH 3.6 and 4.0 and 8 d at pH 5.0. Growth in orange serum was observed prior to the reduction in viable cell numbers at pH 4.8 and 5.0 for both storage temperatures.