Comparison of most probable number (MNP) and membrane filtration techniques for analyzing the natural mineral water microbiological quality

Abstract

Mineral water consumption has been associated with a healthy lifestyle, and many consumers believe that this is a relatively safe product. In Brazil, the RDC no. 275/05 regulates the microbiological standards for mineral and natural waters. This study aimed at comparing the membrane filtration and the most probable number (MPN) techniques for analyzing the microbiological quality of natural mineral water samples bottled into 20-liter containers, commercialized in Rio de Janeiro, Brazil. Of 31 representative samples (a total of 155 units), 22 (70.97%) were unsatisfactory. Among these noncompliant samples, fecal coliforms were detected in two (6.45%). Total coliforms count above the established limit was observed in three samples (9.68%), being enterococci in one sample (3.23%); P. aeruginosa in 21 (67.74%) and sulfite-reducing clostridia in two (6.46%). The MPN technique showed highest sensitivity for detecting the microorganisms groups specified in the above mentioned regulation. Thus, the MPN technique proved to be mostly efficient and suitable for monitoring the microbiological quality of potable waters.