Survival and growth of Pseudomonas aeruginosa in natural mineral water: a 5-year study

A 5-year study was carried out on the growth curve of two strains of P. aeruginosa inoculated at a density of 102 cfu/ml into samples of natural mineral water with different levels of dissolved solids (TDS at 180°C: 72.5 and 382 mg/l) and low organic content (TOC: 0.17 and 0.35 mg/l). The resulting growth curves were similar for both strains, with only slight differences depending on the different amounts of dissolved solids in the water. After 4–5 days counts were increased by 3 log units. This level was maintained until 70–100 days from inoculation, after which a slow decrease began, culminating in the death of one of the strains after 5 years. No difference in recovery was observed between the method using direct inoculation on Cetrimide Agar and the resuscitation technique (preincubation in Tryptone Soya Agar followed by inoculation on Cetrimide Agar) in the exponential phase of the growth curve. During the stationary and death phases, however, the enrichment technique gave statistically slightly higher counts than the selective technique, indicating the presence of damaged P. aeruginosa cells. The use of a resuscitation step when using Cetrimide Agar to assess bottled water quality is recommended.