[extropy-chat] magic johnson, aids, longevity ...

[Robert Bradbury]

On 4/15/06, ben <benboc at lineone.net> wrote:

> Will a combination of antibiotics be less likely to give rise to
> antibiotic-resistant strains of bacteria than using a single antibiotic?


If the antibiotics target different essential aspects the bacteria requires
to be pathogenic (e.g. protein production, cell division, cell wall
maintenance, etc.) then a multi-drug approach will be more successful.

It is easier to acquire resistance by horizontal gene transfer than it is to
create de novo mutations.  Many of the original antibiotic resistance genes
(or a minor variant) probably in bacteria or fungi that needed those
defenses long before humans started discovering and using antibiotics.
Generally speaking one has to have many larger numbers of organisms to get
the right set of mutations when more mutations are required.  Antibiotic
overuse contributes to the possibility that a bacterial strain will evolve
and be selected for that has organized one a single small piece of DNA with
a multi-gene antibiotic resistance set.  The reason to limit antibiotic
misuse or overuse is to attempt to lower the probability of such
developments.

Bacteria for the most part have relatively similar machinery and most of
them have DNA repair mechanisms that make it difficult to create lots of new
mutations on short notice -- millions or billions of years of evolution
between competing organisms in the soil, lakes or water has a much greater
chance of producing weapons and counter-weapons.  Penicillin was produced by
Streptococcus.  Presumably the penicillin resistance genes came from a
different bacterial strain competing for resources with Streptococcus.  The
restriction enzymes in most bacterial species which are key tools in
molecular biology were evolved by bacteria as defenses against bacterial
viruses.  The microorganism world has lots of wars taking place.

And is this the same mechanism we see at work in multi-drug therapies
> for viral infections?


Yes.  HIV has relatively few genes and we are throwing weapons at several of
the most important (Wikipedia has a good discussion [1]).

If antibiotic cocktails are not a good idea, why is this, exactly?


In most cases, you identify the bacteria causing the problem (or at least
species it most probably is) and prescribe the single antibiotic generally
known to be successful.  Only with the emergence of resistant bacterial
strains (esp. in hospitals) are multi-drug approach being given more
attention.  I think the success with the HIV cocktail may be contributing to
people considering this to be a reasonable strategy.  *But* overprescribing
cocktails would increase the probability that you might select for the
strains which can resist more types of antibiotics.  Once bacteria have
acquired "essential" genes it is much harder to lose them -- particularly in
the relatively nutrient rich environment that human hosts provide.

Robert

1. http://en.wikipedia.org/wiki/Antiretroviral_drug
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.extropy.org/pipermail/extropy-chat/attachments/20060415/e237652c/attachment.html>