Heterotrophic plate counts and the isolation of bacteria from mineral waters on selective and enrichment media

The heterotrophic plate counts of 15 brands of bottled non‐carbonated mineral waters were examined and found to be generally high and variable. Four selective or enrichment media for the enumeration of coliforms (m‐Endo LES and m‐lauryl sulphate agar) and Pseudomonas aeruginosa (cetrimide‐nalidixic acid agar and malachite green broth) were used to isolate several species of Gram‐negative bacteria. Strains identified as CDC gr IVc‐2 and Comamonas (Ps.) acidovorans were the two most commonly isolated. Considerable variation in populations was seen between the brands, as well as between two batches of the same mineral water.