[Effect of different dairy products on the growth of Listeria monocytogenes in selective media].

We have studied the influence of the incorporation of milk cream and skim milk on the growth kinetic of Listeria monocytogenes in listeria enrichment broth with 15 mg/l or 7.5 mg/l of acriflavine. Acriflavine was responsible, at least partially, for delayed growth of Listeria monocytogenes in the enrichment broths. A longer lag phase of the growth was produced by the addition of milk cream or skim milk to the enrichment broth containing 7.5 mg/l of acriflavine. However, the maximum population obtained at 48 h did not show significant differences. In the presence of 15 mg/l of acriflavine, we observed a decrease of the viable counts during the early phase of the growth cycle, which was enhanced by the addition of milk cream or skim milk. Moreover, the maximum growth rate was reduced by the addition of skim milk and maximum population was not reached at 48 h. These results suggest the need to validate the methodology of recuperation of Listeria monocytogenes from each dairy product, since its efficiency may be affected by product composition, specially when the sample biocharge is low.