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Re: Antibiotic Treatment of Cyanobacteria

On Sun, 17 Jan 1999, Karen Randall wrote:

> You are certainly right that you need to treat long enough to kill all of
> whatever organism it is you are trying to kill.  I would maintain, however,
> that in my experience, Cyanobacteria _is_ completely killed within the two
> treatments.  I have never had a recurrance after a treatment (except in the
> case of the water fall, which is for different reasons which I have
> explained)  There are certainly a number of types of infections where the
> medical community has found that a shorter treatment period is effective
> than previously thought. (UTI's and ear infections are two types that I
> know of)

The cyanobacteria are normally reduced to a less-than-visible population
within less time than the treatment requires.  Perhaps not wiped out but
certainly reduced to a point where it doesn't rebound in the short term.
But the cyanobacteria in the tank aren't the only microbes that are being
treated by the antibiotic.  Any initially erythromycin-sensitive microbe
in the tank is effected by the antibiotic and could gain resistance from
the repeated use of the antibiotic.  Use of reduced strengths of the
antibiotic is likely to further encourage the development of resistance by
systematically selecting stains that have started to develop resistance.

I don't question the therapeutic effect of short-term treatments for human
ailments, but remember that it was the medical use and overuse of
antibiotics that lead to the development of resistant strains in the first
place.  More recently, the widespread agricultural use of antibiotics has
been implicated.

> Do you have any evidence that resistant forms of Cyanobacteria have
> developed as a result of a full strength two day treatment with Maracyn?
> The reason I specifically _like_ the use of erythromycin for Cyanobacteria
> is that it is already a fairly useless drug for fish diseases.

I haven't heard of any erythromycin-resistant strains of cyanobacteria.  
To that extent the warnings about developing resistant strains are
theoretical, so can you can accept or reject the idea as you see fit.

Also, I don't know what the consequences of erythromycin resistance would
be.  In medicine, as resistance to one strain develops the industry has
just moved on to the next available alternative.  They're running out of
alternatives.  In aquarium keeping we would just move on to another
antibiotic.  I think.  And I hope there are no other resistent pathogens
developed while we do it.

The actual chance of a resistent strain of anything developing in my tank
or in your tank are very slim, but there are millions of aquarists all
over the world and if they are carelessly dosing their tanks with
antibiotics then resistent strains will develop somewhere.

From the standpoint of someone who occasionally gives tank-care advice (my
standpoint) I think it's necessary to advise cautious and appropriate use
of antibiotics.

Roger Miller