A process for detecting and/or semi-quantifying and/or quantifying microorganisms in a solution or suspension, which does not contain pre-cultured microorganisms, comprising the steps of: a) mixing the sample suspected of containing the microorganism with i) a pH buffering suspension, comprising at least one type of paramagnetic particles which have, bound to their surface, a capturing antibody specifically directed against the microorganism which is to be determined; and ii) bovine serum albumin in excess on the surface of said magnetic particles not occupied by the antibody; b) incubating the mixture for a determined time under conditions suitable for forming the microorganism-magnetic particle complexes; c) applying a magnetic field for the separation and concentration of the microorganism-magnetic particle complexes formed; and subsequent evacuation of the supernatant; d) resuspending the microorganism-magnetic particle complexes in a pH buffering solution, comprising at least one type of blocking agent in excess and a second antibody specifically directed against said microorganism at a different site to which the capturing antibody is already attached, labeled with a marker selected from an enzyme or a fluorophore; e) incubating the mixture for a determined time to form the labeled antibody-microorganism-magnetic particle complexes; f) applying a magnetic field for the separation and concentration of the labeled antibody-microorganism-magnetic particle complexes formed; and subsequent evacuation of the supernatant; g) washing the particles to remove the excess of the second antibody specifically directed against said microorganism at a different site to which the capturing antibody is already attached, and subsequent evacuation of the supernatant; h) resuspending the labeled antibody-microorganism-magnetic particle complexes formed in a liquid medium simultaneously containing the substrates necessary for the enzyme marker of 1(d), a blocking agent which is bovine serum albumin at a concentration of 0.1 - 10% thus maintaining the adsorption equilibrium shifted towards the bound blocking agent, and an inhibitor specific for the intrinsic microbial enzymes which compete with said substrates and are selected from the group consisting of sodium azide and triazole at a concentration of 0.01% in a phosphate and citrate buffer solution with a concentration of 50mM, and a substrate, for the marker enzyme, selected from the group consisting of hydrogen peroxide and urea peroxide; i) incubating the mixture for a determined time to develop the signal; j) detecting and quantifying the signal resulting from the formation of the labeled antibody-microorganism-magnetic particle complexes, relating said signal to the presence and quantification of the microorganism sought. a) mixing the sample suspected of containing the microorganism with i) a pH buffering suspension, comprising at least one type of paramagnetic particles which have, bound to their surface, a capturing antibody specifically directed against the microorganism which is to be determined; and ii) bovine serum albumin in excess on the surface of said magnetic particles not occupied by the antibody; b) incubating the mixture for a determined time under conditions suitable for forming the microorganism-magnetic particle complexes; c) applying a magnetic field for the separation and concentration of the microorganism-magnetic particle complexes formed; and subsequent evacuation of the supernatant; d) resuspending the microorganism-magnetic particle complexes in a pH buffering solution, comprising at least one type of blocking agent in excess and a second antibody specifically directed against said microorganism at a different site to which the capturing antibody is already attached, labeled with a marker selected from an enzyme or a fluorophore; e) incubating the mixture for a determined time to form the labeled antibody-microorganism-magnetic particle complexes; f) applying a magnetic field for the separation and concentration of the labeled antibody-microorganism-magnetic particle complexes formed; and subsequent evacuation of the supernatant; g) washing the particles to remove the excess of the second antibody specifically directed against said microorganism at a different site to which the capturing antibody is already attached, and subsequent evacuation of the supernatant; h) resuspending the labeled antibody-microorganism-magnetic particle complexes formed in a liquid medium simultaneously containing the substrates necessary for the enzyme marker of 1(d), a blocking agent which is bovine serum albumin at a concentration of 0.1 - 10% thus maintaining the adsorption equilibrium shifted towards the bound blocking agent, and an inhibitor specific for the intrinsic microbial enzymes which compete with said substrates and are selected from the group consisting of sodium azide and triazole at a concentration of 0.01% in a phosphate and citrate buffer solution with a concentration of 50mM, and a substrate, for the marker enzyme, selected from the group consisting of hydrogen peroxide and urea peroxide; i) incubating the mixture for a determined time to develop the signal; j) detecting and quantifying the signal resulting from the formation of the labeled antibody-microorganism-magnetic particle complexes, relating said signal to the presence and quantification of the microorganism sought.