Differentiation of Staphylococcus xylosus strains from italian sausages by antibiotyping and low frequency restriction fragment analysis of genomic DNA

The aim of this study was to identify the strengths and weaknesses of two typing methods, antibiogram typing and low-frequency restriction fragment analysis of genomic DNA, for the differentiation of Staphylococcus xylosus strains. Twenty-eight Staphylococcus xylosus strains isolated from Italian fermented sausages (Naples-type salami) and S. xylosus DSM 20266 (Type strain) and DSM 6179 were analysed. Antibiotyping, recorded on the basis of susceptibility testing of 16 antibiotics, allowed 21 antibiogram-types to be distinguished. Pulsed-field gel electrophoresis techniques combined with DNA digestion by infrequently cutting enzymes such as Sma I produced 21 pattern-types among the 30 strains of S, xylosus analysed. The association of antibiotyping and PFGE typing clearly distributed S. xylosus strains into 30 combinations, showing that all the strains can be differentiated, Thus, the combination of these two techniques, in spite of limitations due to instability of a phenotype-based system, actually turned out to be the most reliable methodological approach for differentiating strains of S. xylosus.