Purpose: The aim of the study is to compare three different methods, the Italian reference method, the ISO 9308-1:2002 method and a chromogenic rapid method (RAPID’E.coli 2 Agar-Bio-Rad) for the detection of coliforms and E. coli in bottled mineral water.
Methods: The inclusivity and exclusivity of the three different methods were studied using 4 E. coli strains, 10 of other coliform bacteria strains and 35 strains of water-borne pathogens. The LOD of the three methods were defined analyzing 18 bottled of 1.5 liter natural mineral water, spiked with three different concentrations of coliforms or E.coli in presence of competitive bacteria. The ANOVA and Tukey’s Multiple Comparison Test was used for evaluating the comparison among the quantitative results obtained from the three different methods.
Results: The 100% sensitivity and specificity was found comparing the results obtained by the three methods. Both Italian reference method and ISO reference 9308-1 have highlighted difficulties in discriminating colonies of E. coli and coliforms from other Enterobacteriaceae bacterial strains. Chromogenic media do not require any confirmation step of the colonies when it is used for enumerating coliforms and E. coli. Tukey’s Multiple Comparison Test of the means of the counts of E. coli, using the three cultural methods, showed no statistical significant differences.
Significance: The results have demonstrated that the Italian reference method and the new rapid method (RAPID’E.coli 2 Agar-Bio-Rad) are as sensitive and specific as ISO method 9308-1:2002. Both methods could be used in alternative to ISO method to evaluate the contamination level of coliform and E. coli in drinking water, bottled water and mineral water.