The main objectives of this study were to isolate and quantify the major groups of bacteria (Gram positive, Gram negative and nitrogen fixing bacteria) existing in the most common soil types from Moldova and also to report their level of participation and activity for each soil type. Achieving soil samples were taken from differentiated both in terms of composition and their importance agricultural. Classes of soil from which soil samples were taken are cernisoil, luvisoil, salsodisoil, planosoil, protisoil, pelisoil and hidrisoil. Sampling was carried out in two stages (October 2012, May 2013), and to analyze these Petri dishes method was used. By comparing the obtained results a variation between groups of bacteria and main soil types of the Moldova region. Microbiological study results show variations in the concentration and dynamics of Gram positive and Gram negative bacteria. With some exceptions, from the soil types considered in the study species of molecular nitrogen fixing bacteria free aerobic and anaerobic (Azotobacter spp and Clostridium spp.) were isolated. The results illustrate that bacterial flora is strongly influenced by the action of edaphic and climatic factors.