Antibiotics, bacteria, resistance & inherited traits

[Vortigern99]

This paragraph is from an article on Shigellosis, an intestinal infection which is causing some concern in the US at the moment:

Drug resistance develops when bacteria comes into contact with antibiotics at doses that are too low to kill them. When that happens, bacteria adapts to the drug and passes their newly developed resistance on to subsequent generations. It’s unclear exactly why drug-resistant Shigella has increased in the US, but it’s likely that this has something to do with people who don’t finish taking the antibiotics that have been prescribed to them.​

Source: http://www.theverge.com/2015/4/2/8335021/Shigellosis-cdc-drug-resistant-intestinal-illness

Can the highlighted portion be accurate? How does a "newly developed resistance [pass] on to subsequent generations" in any sense, outside of long-debunked Lammarkian evolution theory? Is the writer of the article over-simplifying to the point of garbling the actual process? Please help me understand.

 

[Pulvinar]

As I understand it, the problem isn't that the dose is too low to kill an individual bacterium, but too low to kill them all, leaving just the most-resistant variant(s). Those can then multiply. The antibiotic is providing the evolutionary selective pressure.

 

[Skeptic Ginger]

This paragraph is from an article on Shigellosis, an intestinal infection which is causing some concern in the US at the moment:

Drug resistance develops when bacteria comes into contact with antibiotics at doses that are too low to kill them. When that happens, bacteria adapts to the drug and passes their newly developed resistance on to subsequent generations. It’s unclear exactly why drug-resistant Shigella has increased in the US, but it’s likely that this has something to do with people who don’t finish taking the antibiotics that have been prescribed to them.​

Source: http://www.theverge.com/2015/4/2/8335021/Shigellosis-cdc-drug-resistant-intestinal-illness

Can the highlighted portion be accurate? How does a "newly developed resistance [pass] on to subsequent generations" in any sense, outside of long-debunked Lammarkian evolution theory? Is the writer of the article over-simplifying to the point of garbling the actual process? Please help me understand.

Like Pulvinar says, the organisms that weren't killed lived because they had genetic resistance. When they multiply, the resulting organisms have the same genes of the parent organism. It's basic evolution.

 

[Skeptic Ginger]

But it's more than that, there is also Horizontal Gene Transfer among microbes of different species.

Horizontal gene transfer, or the process of swapping genetic material between neighboring “contemporary” bacteria, is another means by which resistance can be acquired. Many of the antibiotic resistance genes are carried on plasmids, transposons or integrons that can act as vectors that transfer these genes to other members of the same bacterial species, as well as to bacteria in another genus or species. Horizontal gene transfer may occur via three main mechanisms: transformation, transduction or conjugation.


Transformation involves uptake of short fragments of naked DNA by naturally transformable bacteria. Transduction involves transfer of DNA from one bacterium into another via bacteriophages. Conjugation involves transfer of DNA via sexual pilus and requires cell –to-cell contact. DNA fragments that contain resistance genes from resistant donors can then make previously susceptible bacteria express resistance as coded by these newly acquired resistance genes.

 

[Vortigern99]

Like Pulvinar says, the organisms that weren't killed lived because they had genetic resistance. When they multiply, the resulting organisms have the same genes of the parent organism. It's basic evolution.

But it's more than that, there is also Horizontal Gene Transfer among microbes of different species.

A-ha! I shall have to read up on horizontal gene transfer. The article's explanation that "bacteria adapts to the drug and passes their newly developed resistance on to subsequent generations" thing seems Lamarckian to someone like me, who has only studied animal evolution. It's not "basic evolution", it's part of the advanced course!

Thanks for the responses. I'm edified already.

Thanks for the responses.

 

[Dinwar]

Can the highlighted portion be accurate? How does a "newly developed resistance [pass] on to subsequent generations" in any sense, outside of long-debunked Lammarkian evolution theory? Is the writer of the article over-simplifying to the point of garbling the actual process? Please help me understand.

It's an over-simplification.

Antibiotic resistance is a term that subsumes a suite of processes. Basically, the problem with antibiotics is that they go into bacterial cells faster than the bacteria can remove them and muck up vital processes. This provides three ways for bacteria to develop resistance: They can remove the stuff faster than it comes in; they can keep it out in the first place; or they can use processes that aren't affected by the antibiotic. I know that the first option is one that many bacteria take, via adaptations to their ion pumps in the cell membrains; basically, they develop more effective ways to address the chemicals of concern.

The thing is, those more-effective ways to pump antibiotics are already present in most populations of bacteria; there's a heritable variance in efficacy of those pumps. And that's because there's a trade-off. An ion pump is trying to tame Maxwell's Demon; it's trying to push stuff from a low concentration to a high one. Not easy; it requires energy. More effective methods may require more energy--"effective" here refers to how quickly they remove the stuff from the cell, NOT how much they remove per unit of ennergy. So there are advantages in many situations of having less-effective pumps. When you're doused with antibiotic, though, the fitness space changes, selecting for the existing organisms that have the most effective ion pumps.

The Gaia Hypothesis has fallen into disrepute, due to folks abusing it (the Strong Gaia Hypothesis is mystical New-Age nonsense). However, if you look into the origional Daisyworld thought experiment a lot of this will become more clear. Selection can ONLY work with what's there, and creates NOTHING new--it was the greatest counter-argument to Darwin's theory for almost a century. That said, variation is almost ubiquitous in biology, so that's almost never a problem.

 

[Vortigern99]

Thank you, Dinwar. I was hoping you would chime in with your usual erudition on this subject, and you didn't disappoint. I think I have a solid handle on the processes at work now. Thanks to one and all.

 

[Lukraak_Sisser]

There is a fourth option (a variety of method 2 mentioned by Dinwar), the one used by bacteria resistant to penicillin like variants. They secrete a substance that breaks down the antibiotic outside of the cell.
This has the added advantage that a few resistant bacteria can still remove the antibiotic for the whole population.
And randomly developing antibiotic resitance is quite easy (for a given value of easy). The best way, as mentioned, is to use enough of an antibiotic to create a selective pressure, but not enough to kill off a whole population in one go. Once a resistant genotype appears it can be transferred to descendants or trough the aforementioned horizontal gene transfer.

 

[Lowpro]

I approve all of this thread.

 

[abaddon]

This paragraph is from an article on Shigellosis, an intestinal infection which is causing some concern in the US at the moment:

Drug resistance develops when bacteria comes into contact with antibiotics at doses that are too low to kill them. When that happens, bacteria adapts to the drug and passes their newly developed resistance on to subsequent generations. It’s unclear exactly why drug-resistant Shigella has increased in the US, but it’s likely that this has something to do with people who don’t finish taking the antibiotics that have been prescribed to them.​

Source: http://www.theverge.com/2015/4/2/8335021/Shigellosis-cdc-drug-resistant-intestinal-illness

Can the highlighted portion be accurate? How does a "newly developed resistance [pass] on to subsequent generations" in any sense, outside of long-debunked Lammarkian evolution theory? Is the writer of the article over-simplifying to the point of garbling the actual process? Please help me understand.

Yup. Bacteria are effectively one gigantonormous gene pool which can pass on any mutually beneficial mutation to it's brethren at a whim. That's how it is.

 

[CapelDodger]

Yup. Bacteria are effectively one gigantonormous gene pool which can pass on any mutually beneficial mutation to it's brethren at a whim.

As I understand it not all bacteria are in the same fraternity.

 

[CapelDodger]

... the fitness space changes ...

That's a very powerful phrase.

 

[marplots]

(some snipped)
And randomly developing antibiotic resitance is quite easy (for a given value of easy). The best way, as mentioned, is to use enough of an antibiotic to create a selective pressure, but not enough to kill off a whole population in one go. Once a resistant genotype appears it can be transferred to descendants or trough the aforementioned horizontal gene transfer.

And this bit is critical. Let's not forget, the body's native mechanisms are fighting the bacteria as well - you don't really kill all the bugs with an antibiotic anyhow. But you do have to kill enough that the body can deal with the rest.

So, even if you have some antibiotic resistance, you can still cure the infection if you reduce the number of bacteria enough.

Resistance isn't an all-or-none thing. It's more like how much of the forest do you have to protect to stop the wildfire? Some of the trees can burn and go out, sometimes a fire-break will do, and sometimes you better get as many planes dumping stuff as you can.

 

[epepke]

Can the highlighted portion be accurate? How does a "newly developed resistance [pass] on to subsequent generations" in any sense, outside of long-debunked Lammarkian evolution theory?

Um. It kills the ones that are susceptible, and the ones that aren't survive. So they take over the population. Maybe they win.

 

[abaddon]

Um. It kills the ones that are susceptible, and the ones that aren't survive. So they take over the population. Maybe they win.

They do win. Methicillin-resistant staphylococcus aureus is an antibiotic resistant strain of bacteria which resists all treatment except for vanomycin. Until 1997, when strains of MRSA turned up which were now resistant to vanomycin. Evolution is one bad mother.

 

[Dinwar]

There is a fourth option (a variety of method 2 mentioned by Dinwar), the one used by bacteria resistant to penicillin like variants. They secrete a substance that breaks down the antibiotic outside of the cell.

Did not know about that, but it makes sense. All kinds of plants do something similar. Thanks for the info!

 

[commandlinegamer]

They do win. Methicillin-resistant staphylococcus aureus is an antibiotic resistant strain of bacteria which resists all treatment except for vanomycin. Until 1997, when strains of MRSA turned up which were now resistant to vanomycin. Evolution is one bad mother.

A recent news item claimed a ninth-centry remedy found in an old-english manuscript made from onions, garlic and cow bile was up to 90% effective against it.

http://www.bbc.co.uk/news/uk-england-nottinghamshire-32117815

 

[jimbob]

The Long Term Evolution Experiment homepage is worth a browse (see the evolution of citrate metabolism, for example - wiki here)


As an aside:

The fast mutation rate means that if there is no selection pressure for a trait (because an antibiotic is not being used, for example) then it will get lost, like sight in cave fish.

Even better, if there is a cost associated with the antibiotic resistance, that would lead to a selective pressure against the trait in the absence of the antibiotic.

 

[Jodie]

A recent news item claimed a ninth-centry remedy found in an old-english manuscript made from onions, garlic and cow bile was up to 90% effective against it.

http://www.bbc.co.uk/news/uk-england-nottinghamshire-32117815

That's cool, I wonder what other bacteria it would kill besides MRSA? You could whip that up easily enough and keep it handy like neosporin.

 

[Syameese]

That's cool, I wonder what other bacteria it would kill besides MRSA? You could whip that up easily enough and keep it handy like neosporin.

I think the money quote in the article is:

"Experts from the university's microbiology team recreated the remedy and then tested it on large cultures of MRSA."

"large cultures" sounds like this might be just another petri dish miracle, hopefully not, but ...

https://xkcd.com/1217/