Obtaining DNA from Staphylococcus aureus: A study on DNA extraction methods for food matrices without bacterial isolation

Polymerase chain reaction (PCR) is a tool widely used. However, for the effective use of PCR, DNA quality is necessary. Thereby, the objective of this study was to evaluate DNA extraction methods of Staphylococcus aureus, for direct application in food. Five methods were tested using reference and food strains. The methods show different characteristics with steps of thermal lysis, enzymatic lysis, detergents and organic solvent applications. The amplification was carried out using the primers COAG2 and COAG3 and the visualizations of the DNA extracted and amplification products were performed by gel electrophoresis. The method with SDS was not satisfactory using reference strain. The methods based on the use of cetyl trimethyl ammonium bromide (CTAB), sodium chloride-Tris-EDTA (STE) and enzymes showed positive results. Methods 2 (thermal lysis) and 3 (with CTAB) were used for DNA extraction from food samples, without bacterial isolation, and the PCR was subsequently performed. These methods were easier to implement and they show low costs. Thus, the methods 2 and 4 allowed the amplification of the DNA extracted from S. aureus from samples rich in protein and fat. Method 2 is practical and shows other advantages such as less manipulation of samples and reagents, nonuse of contaminant reagents and enzymes, less time for analysis, thus, lower costs.