Incidence of Listeria species in raw and pasteurized milk produced in São Paulo, Brazil.

The present study evaluated the incidence of Listeria spp. in raw and pasteurized milk from a Brazilian dairy plant. Ten samples of each type of milk (raw types B and C and pasteurized types B and C) were collected monthly from October 1989 to September 1990 (except in December), comprising 440 samples (110 samples of each type of milk). The recovery of Listeria spp. was carried out using LPM (lithium chloride phenylethanol moxalactam) and MOX (modified Oxford) agars, after a two-step enrichment procedure in Listeria enrichment broth (LEB) and Fraser broth. Overall, 12.7% of raw milk samples, 0.9% of pasteurized milk samples and 6.8% of total of milk samples were positive for Listeria spp., while 9.5% of raw milk samples, none of the pasteurized milk samples and 4.8% of total milk samples, were positive for Listeria monocytogenes. Raw milk also contained L. innocua (9.5%), L. welshimeri (0.9%) and L. grayi (0.4%). Pasteurized milk contained only L. innocua (0.9%).