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 
tanks overall.

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

   David Aiken                                     email: 
d.aiken at eis_net.au