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The ability to rapidly detect and enumerate ammonia-oxidizing bacteria (AOB) would provide anadditional monitoring tool for the nitrification control strategies of chloraminating utilities.Molecular-based assays were developed and applied to samples from several utilities to evaluatethe feasibility and diagnostic significance of this approach. Two methods were explored, real-timepolymerase chain reaction (PCR) and fluorescent in situ hybridization (FISH). The real-timePCR protocol targeted the amoA gene, separately quantifying Nitrosomonas species,Nitrosomonas oligotropha, and Nitrosospira down to detection limits of approximately 80 genecopy numbers. There was no evidence of matrix interference in analyses of samples spiked witha known number of AOB. Weekly monitoring results show the ability to complement routinechemical and physical water quality monitoring with PCR-based AOB enumeration. With theFISH approach, difficulties were encountered in differentiating AOB from non-target cells due tothe dim probe-conferred fluorescence of the AOB. The protocol was modified to enhance thefluorescent intensity of AOB using multiple probes and tyramide signal amplification (TSA).Both strategies yielded improved fluorescent intensities, with the TSA FISH modificationincreasing AOB intensity by approximately four times. Includes 23 references, table, figures.

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Edition: Vol. - No. Published: 11/15/2004 Number of Pages: 9File Size: 1 file , 520 KB