UNDERESTIMATION OF FECAL-COLIFORM COUNTS IN SHELLFISH-GROWING WATERS BY THE SPANISH OFFICIAL METHOD

We compared two tube fermentation methods for the enumeration of fecal coliforms in mussels: the APHA method and the Spanish official method (CP method). In the study area (Galicia, northwest Spain), the regional authorities have proposed that the CP method be adopted as standard. Results showed that the APHA method gave significantly higher counts (P < 0.01) than the CP method. The mean difference between APHA-method counts and CP-method counts was particularly high when only those samples containing less than 500 fecal coliforms per 100 g (as determined by either method) were considered. A significantly higher number of samples were classified as unacceptable (more than 300 fecal coliforms per 100 g) by the APHA method than by the CP method. These results suggest that the CP method is inappropriate for the enumeration of fecal coliforms in mussels.