Evaluation of an alternative chromogenic method for the detection and enumeration of enterococci in waters

A new chromogenic method for the detection and enumeration of enterococci in water was evaluated using water samples from different sources, specifically, industrial, potable and recreational waters, and compared with the standard methodology for water quality ISO 7899-2. Several statistical parameters, such as relative accuracy, selectivity, efficiency, limit of detection, limit of quantification, inclusivity and exclusivity were determined according to the main criteria provided in ISO 16140 and ISO 17994. An orthogonal regression analysis demonstrated that the developed alternative method performs similar to ISO 7899. The chromogenic medium allowed easy recognition of enterococci by the appearance of pink-colored colonies. Importantly, the method can be executed in only 24 h, showing a similar selectivity (-0.05), a lower limit of quantification (4.08 cfu/100 ml), and a higher efficiency (98%) than the reference method (-0.04; 5.50 cfu/100 ml and 97%, respectively). The results obtained support the use of the alternative method for the detection and enumeration of enterococci to assess water quality from several sources. Key words: Enterococci, chromogenic method, water quality.