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Assessment of Safety of Enterococci Isolated throughout Traditional Terrincho Cheesemaking: Virulence Factors and Antibiotic Susceptibility

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Abstract:

Enterococci account for an important fraction of the adventitious microflora of traditional cheeses manufactured in Mediterranean countries from small ruminants' raw milk and play an important role in the development of suitable organoleptic characteristics of the final product. It has been suggested that animals used for food or animals that supply edible products are a reservoir of antibiotic-resistant enterococci. The main purpose of this research effort was thus to identify, to the species level, a total of 73 enterococci with high tolerance to acidic pH and bile salts (as prevailing environmental conditions in the first portion of the gastrointestinal tract), which were previously isolated from the milk feedstock to the final product of Terrincho cheesemaking, and to determine their profiles of antibiotic susceptibility, coupled with the occurrence of specific virulence factors (especially in those that might eventually be claimed to exhibit suitable probiotic and technological performances). Isolates, identified by both API 20 STREP and PCR methods, were found to belong to the following Enterococcus species: E. casseliflavus, E. durans, E. faecalis, E. faecium, and E. gallinarum. Susceptibility of those isolates was observed to most antibiotics tested, whereas none harbored aminoglycoside resistance genes. PCR screenings for cytolysin genes (cylLL , cylLs , cylM, cylB, and cylA), surface adhesin genes (efaAfs , efaAfm , and esp), the aggregation protein gene (agg), and the extracellular metalloendopeptidase gene (gelE) were performed. All isolates proved negative for cylLL , cylM, cylB, and agg genes. Both E. faecalis strains were positive for the cell wall–associated protein Esp and the cell wall adhesin efaAfs , whereas the cell wall adhesin efaAfm was detected in 11 of the 12 E. faecium strains. Only one strain possessed the cylLs determinant, and another possessed the cylA gene. Incidence of virulence determinants was thus very low; hence, the enterococcal adventitious microflora tested is essentially safe.

Document Type: Research Article

Affiliations: 1: Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Rua Dr. António Bernardino de Almeida, P-4200–072 Porto, Portugal 2: Centro de Genética e Biologia Molecular & Instituto de Cieência Aplicada e Tecnologia, Faculdade de Cieências, Universidade de Lisboa, Campo Grande, P-1749-016 Lisboa, Portugal 3: Instituto de Biologia Experimental e Tecnológica & Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, P-2871-901 Oeiras, Portugal

Publication date: September 1, 2007

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    First published in 1937, the Journal of Food Protection®, is a refereed monthly publication. Each issue contains scientific research and authoritative review articles reporting on a variety of topics in food science pertaining to food safety and quality. The Journal is internationally recognized as the leading publication in the field of food microbiology with a readership exceeding 11,000 scientists from 70 countries. The Journal of Food Protection® is indexed in Index Medicus, Current Contents, BIOSIS, PubMed, Medline, and many others.

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