antibiotic resistance

[axon]

Hello i was wondering how is it possible for bacteria to gain genes responsible for antibiotic resistance , after all, it is obvious that bacteria can not produce new genetic information just because there is an antibiotic in environment .

[hypervalent_iodine]

An individual bacterium does not gain genes that confer resistance over the course of its lifetime, it's that the antibiotics allow for those bacteria that are resistant to survive and those that are not to die. This means that mutations (which can accumulate quite quickly given fast reproductive rates and short generational times) that allow for antibiotic resistance are selected for. One other mechanism that I can think of is via horizontal gene transfer.

[CharonY]

Horizontal gene transfer is probably the biggest contributor to spread of resistance genes. There is also evidence that sub-lethal antibiotics stress can lead to higher mutation rates that can result in the the rise of resistance.

It should be noted that resistance mechanisms do not necessarily require new genetic material but a simple point mutations e.g. in the ribosomes can prevent antibiotic action (depending on the mechanisms, of course).

 

But other than that as already pointed out it is mostly a selection of existing resistant strains.

Edited December 9, 2013 by CharonY

[axon]

but if the genetic material of bacteria is shared by plasmids does it mean that the material is altered between plasmids and nucleoid or that mutations occur in the genetic material of plasmids? it is interesting thing because i thought that plasmids do not change with time . I apologize for grammatical mistakes if any, occured but English is my second language and thanks for the replies .

Edited December 9, 2013 by axon

[CharonY]

Plasmids undergo mutations just like everything else. The rate and frequencies can vary somewhat from the chromosomal DNA because a) of different base composition and b) different replication apparatus. However, if anything plasmids tend to evolve faster as they usually do not carry essential functions (i.e. there is less selection to conserve sequences).

[Andrew Polyak]

This question seems more like a question of evolution. A bacteria doesn't just decide, "hey, I'm going to be hydromycin resistant today!". The change is actually quite by chance. These chance mutations start evolution over many generations, and can be passed to another through chance methods like homologus recombination. These resistant bacteria can now be selected for!

[kikicic]

It is important to note that these mutations do not occur because of the interaction with the antibiotics,they occur by chance and the overall resistence is a product of resistent bacterias(the ones where the mutation occured by chance) multiplying and creating large numbers of resistant bacterias(some of them can also mutate back to the original state and lose their resistance).