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Listeria monocytogenes and Salmonella spp. in Raw Milk Produced in Brazil: Occurrence and Interference of Indigenous Microbiota in their Isolation and Development

Authors

  • L. A. Nero,

    1.  Departamento de Veterinária, Universidade Federal de Viçosa, Campus Universitário, Viçosa, Brazil
    2.  Departamento de Alimentos e Nutrição Experimental, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, São Paulo, Brazil
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  • M. R. De Mattos,

    1.  Departamento de Medicina Veterinária Preventiva, Universidade Estadual de Londrina, Campus Universitário, Londrina, Brazil
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  • M. De Aguiar Ferreira Barros,

    1.  Faculdade de Agronomia e Veterinária, Universidade de Brasília, Campus Universitário Darcy Ribeiro, Brasília, Brazil
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  • M. B. T. Ortolani,

    1.  Departamento de Veterinária, Universidade Federal de Viçosa, Campus Universitário, Viçosa, Brazil
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  • V. Beloti,

    1.  Departamento de Medicina Veterinária Preventiva, Universidade Estadual de Londrina, Campus Universitário, Londrina, Brazil
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  • B. D. G. De Melo Franco

    1.  Departamento de Alimentos e Nutrição Experimental, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, São Paulo, Brazil
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L. A. Nero. Departamento de Veterinária, Universidade Federal de Viçosa, Campus Universitário, s/n. 36570 000 Viçosa, Minas Gerais, Brazil. Tel.: +55 31 3899 1463; Fax: +55 31 3899 2317; E-mail: nero@ufv.br

Summary

This study aimed to verify the occurrence of Listeria monocytogenes and Salmonella spp. in raw milk produced in Brazil. On account of the poor microbiological quality of this product, possible interference from the indigenous microbiota in these pathogens was also evaluated. Two-hundred and ten raw milk samples were collected in four important milk-producing areas in Brazil, 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 in any raw milk sample, but poor microbiological quality was confirmed by the 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. Three-hundred and sixty raw milk strains were tested for antagonistic activity against both pathogens, and 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 species, mainly Lactococcus lactis subsp. lactis and Enterococcus faecium, known by antimicrobial substance production.

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