Application of an amperometric immunosensor for the enumeration of Nitrobacter in activated sludge

A competitive immunosensor using a monoclonal antibody has been developed f or the enumeration of Nitrobacter in activated sludge and other environment al samples. Its cross-reactivity was tested against a number of bacterial s trains and isolates. All strains of the nitrite-oxidising genera Nitrobacte r and Nitrococcus reacted strongly with the monoclonal antibody. The nitrit e-oxidising Nitrospira moscoviensis, as well as the ammonia oxidising bacte ria and the heterotrophic bacteria tested, did not show any affinity toward s the antibody in the immunosensor. The numbers of Nitrobacter were analyse d in sludge samples from several wastewater treatment plants in Sweden. Det ectable amounts were found in all samples. This study shows the adequacy of using this immunosensor for the enumeration of Nitrobacter in natural envi ronments.