(antibiotic) Bacterial resistance mechanisms

[hitmankratos]

Hello everyone,

 

I know there are a lot of informations on this on the internet, but I just can't find something vulgarised. All is too complicated, or too simple (for a Grade 10 student).

Ok, so I've read there are many ways bacteria can aqquire an antibiotic resistance. The most common is with the plasmids. Where do these plasmids come from in the first place? Is it a mutation?

I've also read that bacteria can mutate and get a resistance that way...How does that happen?

Any other ways for aqquiring an antibiotic resistance?

 

Thanks in advance.

[iNow]

Hi Hitman,

 

Let me start by saying I'm not a biologist, and I'm not formally trained in this, but I'm pretty sure the best explanation is evolution through natural selection. Basically, you have the bacteria in the system. Then, the antibiotic is introduced. That antibiotic kills a large percentage of the bacteria, but some will survive (likely due to some mutation as you mentioned). Then, those which have this mutation are the only ones to reproduce, since they are the only ones which survived. They create offspring (new generations of bacteria) which have that same mutation which made them resistant, and they too survive and reproduce, spreading the resistence to later generations. So, sooner or later, the antibiotic has killed all of the ones that weren't resistent and the ones which were resistant were able to continue reproducing, until eventually the majority of the bacteria are able to survive against the antibiotic and the antibiotic is no longer effective.

 

Now, once you get started talking about plasmids and causes for mutation, you're pretty far beyond my knowledge level and I will need to remove myself from the discussion. Good luck, and have fun.

[CharonY]

Maybe one should start off how antiobiotics (ABs) work. Most ABs inhibit protein synthesis or by binding at the ribsomes (the "proten factory" of the cell) but they can also effect specific enzymes. Given the fact that in these cases the function of the ABs requires effective binding to their targets, a possibility of resistance is to have a mutation that alters this binding sites, so that the AB does not bind anymore. These mutation can occur randomly and once ABs are present there is a selective pressure to maintain these mutations (provided they do not inhibit the primary functions of the ribsomes/enzymes, of course).

This kind of resistance is generally not transmissible. However, target proteins may be protected against ABs by certain modification by other enzymes, which in turn can be propagated across a population via horizontal gene transfer (of which plasmids are one means).

 

Other means of resistance include:

 

-prevention of the entry of ABs into the cell: many ABs are transported into the cell actively. The cell does not do it on purpose, of course, but the ABs may be co-transported by transporters. Modification of these transporters may enable the bacterium not to import ABs

 

-inactivation of ABs by modification or cleavage

 

-export of the ABs: some bacteria possess export system that effectively pump out ABs so that the intracellular concentration remains low.

 

Now regarding the evolution of plasmids: this is a very interesting topic but I think it deserves a thread on its own.

[Mr Skeptic]

Some of the resistance genes seem to have been acquired directly from the organism which made the original antibody. Bacteria will occasionally incorporate DNA into their genome. In the case of natural antibiotics, usually there already exist bacteria with resistance to it, and the resistance can be transferred even across species (bacterial conjugation is very liberal). In some cases, a random mutation will make a bacteria resistant or immune to an antibiotic.

 

However the resistance is acquired, once the resistance is acquired and the antibiotic in use, natural selection will increase the proportion of bacteria that are resistant.