Decoding the multiple tube fermentation method used in coliform testing

Abstract

The multiple tube fermentation method (MTFM), used worldwide for decades in coliform testing, consists of the detection of the presence of total coliforms as the first step and fecal coliforms as the second step. The results obtained during the MTFM can be used to enumerate the relevant organisms detected in each step in terms of the most probable number (MPN). This research was carried out to find out whether it would be possible to omit the total coliform test and start the MTFM with the fecal coliform test. Minimum concentration of Escherichia coli (E. coli) in an aqueous suspension was obtained by means of a dilution series and was subjected simultaneously to the two tests. The results indicated that both tests responded identically to E. coli by showing no statistically significant differences (p > 0.05) between the MPN counts, even to very low numbers of the bacterium, which is often the condition of the samples tested by the MTFM in the real world. Accordingly, it was concluded that there was no scientific requirement to perform the total coliform test to commence the MTFM for the detection and enumeration of E. coli, and, instead, the procedure can be initiated with the fecal coliform test without compromising the accuracy of the outcome.