szena

How can a bacterium get "used to" something that is meant to be fatal to it?

10/3/2007 3:57:08 AM

David B.

@szena:

The same way we can get used to poisons like arsenic. If you are not exposed to a fatal dose, you can build up a tolerance over time.

Magus55 appears to be arguing that anti-biotic resistance is the result of a bacterium's increased tolerance to ABs in the face of weak exposure, combined with the asexual nature of bacterial division.

Unlike us, bacteria do not 'reset' their physiology from one generation to the next. The 'children' of a dividing bacterium will have the same biochemistry active in their cells as their parent as well as the same genome. Hence a reaction to a non-fatal exposure to antibiotics could be passed on in a very Lamarkian fashion.

But this is clearly not what actually happens. Analysis of the genomes of resistant and susceptible strains of the same bacterial phylotype show that the difference is genetic. Culturing resistant bacteria without antibiotics does not lead to a sudden reversion to susceptibility (just gradual genetic drift).

Magus55 is right that AB resistance on its own is a poor example of evolution, as (unlike in, say, fungicide resistance) a feasible alternative explanation can be given. However, he is wrong about how bacteria gain resistance, and wrong that evolution cannot occur over a couple of days, or in a school bio lab.

10/3/2007 4:37:02 AM

cyborgtroy

Bacteria are lifting weights?

10/8/2007 11:02:21 AM

Caustic Gnostic

Very very good example of ignorance.

The last bit is pretty much true. Too bad it reads like a non-sequitur.

10/8/2007 11:14:50 AM