Phenotypic and genetic diversity of enterococci isolated from Italian cheeses

Abstract

In the present study, 124 enterococcal strains, isolated from traditional Italian cow, goat and buffalo cheeses, were characterized using phenotypic features and randomly amplified polymorphic DNA polymerase chain reaction (RAPD–PCR). The RAPD–PCR profiles obtained with four primers and five different amplification conditions were compared by numerical analysis and allowed an inter- and intraspecific differentiation of the isolates. Whole-cell protein analysis by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) was used as a reference method for species identification. The strains were identified as Enterococcus faecalis (82 strains), E. faecium (27 strains), E. durans (nine strains), E. gallinarum (four strains) and E. hirae (two strains). Species recognition by means of RAPD–PCR was in agreement with the SDS–PAGE results except for eight strains of E. faecium that clustered in separated groups. On the other hand, phenotypic identification based on carbohydrate fermentation profiles, using the rapid ID 32 STREP galleries, gave different results from SDS–PAGE in 12·1% of the cases. The majority of the strains had weak acidifying and proteolytic activities in milk. One E. faecium strain showed vanA (vancomycin resistance) genotype while four strains showed a β-haemolytic reaction on human blood. Several strains showed antagonistic activity towards indicator strains of Listeria innocua, Clostridium tyrobutyricum and Propionibacterium freudenreichii subsp. shermanii.