Listeria monocytogenes and Salmonella spp. in raw milk produced in Brazil: occurrence and interference of indigenous microbiota in their isolation and development.

摘要

Occurrence of Listeria monocytogenes and Salmonella spp. in raw milk produced in Brazil was investigated. On account of the poor microbiological quality of this product, possible interference from the indigenous microbiota was also evaluated. 210 raw milk samples were collected from 4 important milk-producing areas in Brazil. They were tested for L. monocytogenes and Salmonella spp. presence, and for enumeration of indicator microorganisms: mesophilic aerobes; total coliforms; and Escherichia coli. The interference of the indigenous microbiota in the isolation procedures was also tested, as well the frequency of naturally occurring raw milk strains with antagonistic activity against both pathogens. The pathogens were not isolated from any raw milk sample, but poor microbiological quality was confirmed by high levels of indicator microorganisms. When present at high levels, the indigenous microbiota generated an evident interference in the methodologies of L. monocytogenes and Salmonella spp. isolation, mainly when the pathogens appeared at low levels. 360 raw milk strains were tested for antagonistic activity against both pathogens. 91 (25.3%) showed inhibitory activity against L. monocytogenes and 33 (9.2%) against Salmonella spp. The majority of the antagonistic strains were identified as lactic acid bacteria, mainly Lactococcus lactis subsp. lactis and Enterococcus faecium, known by antimicrobial substance production.