Evaluation of the Most Probable Number Technique for the Enumeration of Fecal Coliforms and Pseudomonas aeruginosa in Sediment

    Published: Jan 1979

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    This study was designed to demonstrate the magnitude of the bias of the most probable number (MPN) test when applied to sediment. Sterile sediment samples were inoculated with fecal coliforms or Pseudomonas aeruginosa organisms, and recovery by MPN and plate count procedures was compared. The five-tube MPN estimates fluctuated between 43 percent above and 65 percent below the plate count when tests were performed with a 1:10 dilution of sediment inoculated with fecal coliforms. A 1:100 dilution of sediment produced an under-estimation in the counts of 86 percent. Analysis of the MPN expression for P. aeruginosa in sediment showed that with a 1:10 dilution, the numbers could vary from 39 to 98 percent below the plate count. The average underestimation for the 1:100 dilution was 90 percent. These results showed that, unlike water samples, which may have an 18 percent bias on the high side of the “true” population, sediment samples analyzed by the common 5-5-5 tube MPN technique yield a significant underestimation of the actual bacterial count.


    sediment, most probable number, Pseudomonas aeruginosa, fecal coliforms, evaluation, plate count

    Author Information:

    Seyfried, PL
    Associate professorassociate professor, University of Toronto, Toronto, Ontario

    Owen, ARG
    Associate professorassociate professor, University of Toronto, Toronto, Ontario

    Committee/Subcommittee: D19.07

    DOI: 10.1520/STP38140S

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