Procedure for the specific isolation of total DNA content of bacterial germs of different samples, in the course of which the cells are lysated, the DNA content of the lysate is bound selectively, it is washed and then the desalinated linear polymer nucleic acid is eluted from the binding surface in an aqueous solution. Before cell lysis the nonviable bacterial cells are separated from the viable cells on the basis of their different cell surface physical-chemical characteristics, the viable cells of the sample are kept and then lysated using a mechanical and/or enzymatic, favorably lysozyme enzymatic method. After this exclusively double-stranded DNA deriving from the lysate of viable cells is bound on a —SiO2—TiO2— matrix containing chemically activated —OH and dodecylamine groups, and after washing it, the desalinated linear polymer nucleic acid is eluted in an aqueous solution.