Ecology of antibiotic resistant coagulase-negative staphylococci isolated from the production chain of a typical Italian salami

Bacteria carrying antibiotic resistance (AR) genes may represent a hazard for human health. The objective of this study was to evaluate the relationship between the origin, cell number, biotype, phenotypic and genotypic AR profile of coagulase-negative staphylococci (CNS) isolated from the production chain of Salame Piacentino. The 390 isolates were genetically ascribed to 98 different strains belonging to 13 Staphylococcus species: Staphylococcus xylosus and Staphylococcus pasteuri were the predominant followed by Staphylococcus hominis, Staphylococcus cohnii and Staphylococcus epidermidis. Eight antibiotic resistant strains, isolated from skin and salami samples, were detected in different steps along the manufacturing process. Determination of the minimum inhibition concentrations of all CNS strains showed a high frequency of phenotypic tetracycline and erythromycin (83.7% and 68.4% respectively) and a lower kanamycin (40.8%) resistant. The most frequently detected AR genes were ermC (37.8%), tet(L) and tet(K) (31.6% and 34.7% respectively) mainly in skin before washing with water at 65 °C and in faeces samples, but only S. xylosus harbouring tet(K) gene was detected during the salami ripening. Our findings show that, the production chain of Salame Piacentino is a source of antibiotic resistant CNS, but the salami manufacturing process leads a strong reduction of the antibiotic resistant strains and the hazard for human health.