Re: legionella bacteria in aquaria?
On Wed, 22 Jan 1997 Douglas C. Skokna asked:
>Also, does anyone know of instances of "Legionnaires" bacteria being
>present in either RO/DI storage units or in aquariums? If I recall, the
>"Legionnaires" bacteria will grow in untreated water such as roof top
>cooling water units if not trreated.
I work in occupational health and safety and have had a little experience
with cooling towers of air conditioning systems that have tested positive
for legionella bacteria.
First, these bacteria are quite common in the environment and get carried
into the cooling towers on dust, vapours, etc with all sorts of other
bacteria. The towers provide a good environment for some of these
bacteria to breed and sometimes things get especially congenial for
legionella and problems arise.
Second, what surprised me when I started to find out about this problem
the hard way was just what the construction of a cooling tower resembled.
To put it quite bluntly, it's like an <expletive deleted> great trickle
filter!!!! We use large surfaces to promote bacteria growth, they use it
to promote evaporation and cooling. But, boy, can they get explosive
bacterial growth at times! Shows you why trickle filters are effective.
I guess that legionella bacteria might grow in aquaria since I have
reliable reports of aborigines in the Australian outback who have never
been near an air conditioned building, or even any real outpost of
civilisation as we know it, who have antibodies to legionella. This
indicates that they have been exposed to the bacteria at some time, and
that exposure has been traced to creeks and billabongs. These creeks and
billabongs are, quite likely, the native habitat of some species of
Australian rainbowfish and if those are viable in the home aquarium I
can't see why the local bacteria wouldn't be also. What may be a limiting
factor is that the kind of surfaces they like to colonise are plentiful
in the wild but might not in aquaria. These are not free swimming
bacteria - they need a suitable surface to colonise - and those surfaces
may not be the sort of surface we encourage in our tanks. Rotting
vegetation, etc, is plentiful in nature but we don't encourage it in our
tanks. I really don't know what sorts of surface legionella like in the
wild so I can't give definite info on this aspect.
I have heard of one possible case of someone catching legionaire's
disease from an aquarium but it was not proven. There may well have been
a different source. If it was the aquarium, the tank was low tech, driven
by an air stone which causes the surface to break, and may have generated
the aerosol necessary to get the bacteria to the person's lungs. It was
also incredibly dirty - green with algae and poorly cared for. Breaking
the surface forces CO2 out of solution, which we don't like in planted
tanks, nor do we like dirty tanks (all those postings about algae :-) ).
Maybe keeping the surface relatively unbroken and the tank clean are
safety factors. That also fits with Marshall Wilkinson's comments about
the good guys out-competing the bad guys, and the desirability of clean
In any event, one possible case out of hundreds of reported cases over
umpteen years does not indicate a very high degree of risk. Knowing what
I know, I'm not losing any sleep over the risk and I intend to continue
playing happily with my tank.
David Aiken email:
d.aiken at eis_net.au