Bacterial DNA of the Bifidobacterium and Lactobacillus genera were isolated from complex samples by magnetic carriers containing carboxyl groups on the surface and cobalt ferrite particles modified with different agents. These particles reversibly bind DNA in the presence of poly(ethylene glycol) (PEG 6000) and sodium chloride. A more expressive DNA adsorption was achieved at a PEG concentration > 5% and at a NaCl concentration > 1%. The procedure developed was used for isolation of bacterial DNA from crude cell lysates of different dairy products (butter milk, cheese, yoghurt, probiotic tablets) or from lyophilisates. No phenol extraction of DNA or cell cultivation was necessary. The presence of bacteria of the Bifidobacterium and Lactobacillus genera was identified by PCR amplification.