A modified Gauss-Newton algorithm and ninety-six well micro-technique for calculating MPN using excel spreadsheets

Conventional most probable number (MPN) methods seek a calculated value for microbial concentration (Delta, mL(-1)) which induces the total binomial p robability function (P-total) to approach its maximum limit. In fact, such techniques are the only statistically compelling procedures available for d etermining MPN when utilizing a small set of observations per dilution (e.g ., n = 3-8). However, as n approaches a large value, statistical routines w hich assume a normal distribution might be applied to ascertain the MPN. Wi th this in mind, we produce herein a modified Gauss-Newton "linearization" (curve fitting) algorithm for determining Delta (n = 96) from binomial micr o-plate assays which are readily automated using 96-well micro-plate reader s. This technique, an iterative protocol, is less cumbersome than many trad itional MPN procedures and has certain advantages. Data derived from this m ethod were not only close to MPN estimations using a direct technique based on the conventional maximum probability resolution (MPR) concept but also displayed more favorable chi-squared (chi (2)) statistics.