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Abstract
We studied the influence of electrolytically released copper and silver ions on the
microbiological quality in a warm water system of a hospital. The concentration of
nontuberculous mycobacteria was followed for three, and that of legionellae and other
heterotrophic bacteria in the water for four years. The highest concentrations of
copper and silver ions were 220 and 68 microg/l, respectively. Silver ion concentration
of about 3 microg/l was sufficient to control the growth of legionellae in circulating
warm water. The results showed that it is more difficult to eradicate legionellae
from taps and showers: these points were colonized by a small number of legionellae
after the metal ion concentrations were increased in the circulating water. A regular
use of water eradicated legionellae from the shower. One tap was still used irregularly,
and this may be a reason why it still contained small concentrations of legionellae
also in the last years of the study. Mycobacteria were occasionally isolated from
the circulating water and repeatedly from the shower, even when the metal concentrations
were high. To control legionella bacteria in warm water systems, silver concentrations
of only 3 microg/l are needed if all taps and showers of the system are regularly
used. Such low copper and silver concentrations, however, are not efficient against
nontuberculous mycobacteria or other heterotrophic bacteria.