A simple nutrient-tolerance (NT) test for the characterization of the different types of oligocarbotolerant and oligocarbophile water bacteria from non-carbonated mineral water.

Comparative determination of the specific growth kinetics in mineral water and low and higher concentrated broths at 20 degrees C of 25 selected Gram-negative bacteria isolated from natural non-carbonated mineral water yielded three groups: (1) facultative oligocarbotolerants--with faster growth in normal broth (In g l-1: yeast extract 2.5; casein peptone 5.0; glucose 1.0); (2) obligate oligocarbotolerants--with equal rates of growth in normal and 1:10 diluted broth; and (3) oligocarbophiles--with faster growth in 1:10 diluted broth and in mineral water. In addition, three nutrient types, 'eu-, meso- and oligotrophic' could be distinguished on the basis of full, weak and no growth in brain-heart infusion broth. Further characterization was made between slow and very slow growth types in 1:10 diluted broth. All 25 isolates were psychrotrophic with a minimum growth temperature below 0 degree C. The optimum and maximum temperatures of growth in 1:10 diluted broth, as determined in a temperature gradient incubator were between 20 and 32, and between 29 and 34 degrees C with an average of 26 and 31 degrees C, respectively. Based on these results a very simple nutrient-tolerance test was proposed. After inoculation of the three media, 1:10 diluted broth, normal broth and brain-heart infusion, it is only necessary to check whether or when visible turbidity occurs during 2 weeks incubation at 20 degrees C. This allows additional characterization of bacteria from natural mineral water, which are often difficult to identify, on the basis of growth characteristics in various types of nutrient media.