[spanktar]

I think the real meat of this article is here:

"...strikes multiple targets, including cell walls...Since the lipid structures it attacks don’t evolve as quickly as frequently mutating proteins, it may take the bacteria longer than usual to develop a survival tactic."

Proteins change often and quickly, but basic cell structures may take longer or never adapt.

But I'm not a pathobiologist, I just play one on the Internet

[hga]

So do the β-Lactam antibiotics (e.g. penicillin), but that doesn't stop a host of unrelated resistance mechanisms: enzymes that directly attack it, mutations to the protein(s) that are necessary for entry into the bacteria, and probably the pumps that actively remove various antibiotics.

Given that this was discovered from existing bacteria, there's a significant chance nature has already done the first and last of those. The middle mechanism is likely possible for any bacteria, if you have enough to start with (there's nothing I could find with Google in a minute to describe teixobactin's transport mechanism).

In general there was a rule of thumb when I was doing microbiology of this exact nature (an antibiotic created by some strains of E. Coli), if you exposed a million bacteria cells to a generic antibiotic, 1 would would survive due to a mutation (a useful number in microbiology, likely dead meat in the body). Streptomycin was more effective, 1 in a billion.

ADDED: it's implied by the Nature abstract that the researchers have tried this general approach, that they were not able to find spontaneous resistance mutations in a couple of the standard nasties. But extending on the above thesis, ecologically, there's a respectable chance some bacteria out there have developed defenses. It's a jungle out there, and e.g. in your gut, that's why fungi and bacteria developed antibiotics in the first place. They aren't expending resources just to allow us to kill the inconvenient ones.

[pcrh]

From the Nature article, the claim that resistance to teixobactin is hard is based on an attempt by the authors to induce resistance by culturing S. aureus or M. tuberculosis in the presence of sub-lethal concentrations of teixobactin for 27 days and seeing if resistant clones evolved. They did not observe any. That doesn't mean it's impossible, though. Plasmids for example are a source of resistance that doesn't require mutations.

Edit: deleted incorrect information about b-lactamase.

[hga]

[ Deleted β-Lactam stuff. ]

Nature asked me for $$$ to read the article, so ... from your description, that's leaving out the hard, fast test of just culturing several billion of those, adding a lethal concentration and seeing if there are any survivors. Which is how I gather one found spontaneous transport mutations, at least circa 1977. The state of the art has likely improved, and these guys used novel microbiological methods to find the bacteria that produce teixobactin in the first place.

ADDED: thanks to betatim's link to the full text, I've skimmed it and read the discussion, and teixobactin sound quite promising. They haven't found any protein to which it binds, and they think it binds to an "Achilles's heel" in the outer cell wall. The method described to generate resistance was their most extreme attempt, so I assume they tried the fast way, and I can see why it didn't work.

Ecologically, they believe there's little gene (e.g. plasmid) transfer between these soil bacteria and human pathogens, and the "30 year" bit came from experience with vancomycin, to which it has a lot of similarity. And they've done lots of tests for human toxicity and effectiveness in mammals. It's still early in the process, but a degree of fuss is warranted, especially due to their discovery method.

[pcrh]

Here are the pertinent bits regarding resistance, in summary it implies that spontaneous resistance will be difficult, But... "life has a way":

>We were unable to obtain mutants of S. aureus or M. tuberculosis resistant to teixobactin even when plating on media with a low dose (4 X MIC [minimal inhibitory concentration]) of the compound. Serial passage of S.aureus in the presence of sub-MIC levels of teixobactin over a period of 27 days failed to produce resistant mutants as well (Fig. 2d, Supplementary Discussion)

From the Supplementary information:

>Cells were added to teixobactin present at 0.25xMIC, 0.5xMIC,1xMIC,2xMIC and 224xMIC. At 24 hour intervals, the cultures were checked for growth. Cultures from the second highest concentrations that allowed growth (OD600≥2) were diluted 1:100 into fresh media containing 0.25xMIC, 0.5xMIC,1xMIC,2xMIC and 4xMIC of teixobactin. This serial passaging was repeated daily for 30 days. Any cultures that grew at higher than the MIC levels were passaged on drug free MHA plates and the MIC was then determined by broth microdilution. No resistant mutants were obtained. This experiment was repeated, and produced the same negative result. In order to maximize the chance of obtaining a resistant mutant, we performed an additional experiment with very small incremental increases in the drug concentration. Cells were added to a series of tubes with small differences in the concentration of teixobactin (0.06xMIC, 0.25xMIC, 0.5xMIC, 0.75xMIC,1xMIC, 1.25xMIC, 1.5xMIC, and 2xMIC). At 24 hour intervals, cultures from the highest concentration that allowed growth to a minimum OD600 of 0.2 were diluted 1:100 into fresh medium containing 0.06xMIC, 0.25xMIC, 0.5xMIC, 0.75xMIC,351xMIC, 1.25xMIC, 1.5xMIC, and 2xMIC. This passaging was repeated for 27 days. Cultures that grew at levels higher than the MIC were passaged on drug free MHA plates, and the MIC was determined. For teixobactin, there were no mutants with an MIC greater than the parent S. aureus ATCC 29213.

[timr]

What they're describing here is an intensive selection process for resistance. It's debatably much more intensive than nature would ever perform: they're growing bacteria in the presence of various dilutions of the antibiotic, taking a sample of the culture, diluting it 100-fold, and repeating the selection many (~30) times. Then they look for any bugs that develop resistance. None were found. Even if you had a truly pathological patient (i.e. someone who was doing his level best to mis-use an antibiotic), it wouldn't come close to this level of selective pressure for antibiotic resistance.

Moreover, there's a strong biochemical argument against resistance: the region that the antibiotic targets is highly conserved, which means that it's probably functionally necessary. The bug is therefore unlikely to evolve away from the threat. This is important, because it's that most likely avenue for antibiotic resistance, energetically speaking: it doesn't cost anything for an organism to mutate a weakly conserved gene, so they do it once, and pass it on to every subsequent generation with no penalty.

The antibiotic is just a peptide, so in theory you could see some sort of specialized peptidase evolve from an existing gene...but the problem is that the bug would have to then carry around that gene and express it constantly (or even less likely: evolve a sensing system that allows for selective expression). It's a highly unlikely thing, and virtually impossible to maintain over multiple generations without constant selective pressure. Bacteria do not like to hold on to genes that they don't need.

Nothing is impossible over evolutionary time, of course, but the researchers don't seem to be overstating their case here.

[pcrh]

Without having read the article too closely, teixobactin appears to be binding the lipids of the bacterial cell wall. It might be hard to evolve simple resistance to this (and the authors support this by experiment) as this would require that the bacterium changes the composition of its membranes, rather than evolve a mutated enzyme, which is how most spontaneous resistance occurs.

However, that does not exclude the possibility of the bacterium acquiring a plasmid or phage carrying an enzyme that inactives teixobactin. This particular mode of acquiring antibiotic resistance is quite common.

Nevertheless, this finding does seem to be quite a big deal. A novel broad-spectum antibiotic where spontaneous resistance is unlikely is a pretty powerful addition to the pharmacopeia.

[fraserharris]

Removed anthropomorphising:

It's a highly unlikely thing, and virtually impossible to maintain over multiple generations without constant selective pressure. Bacteria are quickly out-competed by genetic variants with fewer expressing genes that they don't need.

BTW: do you have any links/data re the relative 'cost' of expressing unneeded genes?

[randall]

Tim you can do anything. Omniref or help me understand wtf just happened. :)

[politician]

If the antibiotic is abused by an entire society, then it'll end up in the water supply just like caffeine, birth control drugs, and Prozac.

[Fomite]

No. Beta-lactams inhibit cell wall synthesis by binding with penicillin binding proteins and preventing their function. Beta-lactamase is a resistance mechanism against this family of drugs.

[pcrh]

You're correct, I'll correct my post.

[giarc]

Microbiologist here. Your last sentence is perhaps not correct, or else I am not understanding it well enough.

Plasmids are indeed a source of resistance, but plasmids just contain genetic code. They are considered mobile since they are easily transferable between bacteria (including different species). So for a plasmid to encode resistance to this new antibiotic, it would need to contain the code for a protein which disrupts the action for the antibiotic. For example, the plasmid would encode for an enzyme that digests the antibiotic at a faster rate than it can work, or bind to the target of the antibiotic with a higher affinity.

So maybe what you were getting at is that a plasmid exists out in the world that encodes the protein for resistance, it just didn't happen to exist in the researchers niche world, or doesn't rely on a random mutation to become a resistance product.

[hga]

So maybe what you were getting at is that a plasmid exists out in the world that encodes the protein for resistance, it just didn't happen to exist in the researchers niche world....

Per cowsandmilk the senior author of the publication "is one of the world's foremost experts on antibiotic resistance". The paper discusses how there seems to be little gene transfer between the "biome" of soil bacteria from which this and vancomycin come and the relevant pathogens. They specifically cite that it took 30 years for any resistance to develop to vancomycin.

Whereas I'd add β-Lactam antibiotics seem to be pretty common (they are derived from at least 5 different organisms that I just counted in Wikipedia), and β-Lactamases are all too common; per Wikipedia https://en.wikipedia.org/wiki/Beta-lactamase the first was discovered in 1940 before penicillin was in clinical use.

[Natsu]

It's too bad there's no easy way to make resistance work for us, instead of against us. Like finding something else for these to infect, having them get resistance to the nasty bug, then using the same method to get rid of it.

[gus_massa]

Many of the antibiotics are made naturally by fungus to combat bacteria. Once discovered, we just create a synthetic method to prepare them, and perhaps improve the effectiveness and reduce the collateral effects. The canonical example is penicillin http://en.wikipedia.org/wiki/Penicillin#History

[eru]

You might be interested in phage therapy. A phage is a virus that attacks bacteria. (https://en.wikipedia.org/wiki/Phage_therapy)

[maurycy]

What is the exact name for the survival mechanism you described?

[hga]

Errr, spontaneous mutation?? Selection pressure for such mutations that are still survivable for the bacteria?

I just described a very rough screening method, pcrh quotes from the Nature article other extreme efforts tried. These don't produce specific types of mutations, they just discover if there are any "easy" ones. E.g. the E. Coli antibiotic I mentioned had to be transported across the membrane bacterium by a protein.

The lab I did part of a summer's research was working with the enterobactin iron scavenging mechanism in E. Coli (https://en.wikipedia.org/wiki/Enterobactin). If grown in seriously iron free condition (e.g. glassware was soaked in HCl, and then bathed in deionized water for days), it would synthesize iron binding enterobactin and send it out into the environment, and there was a protein on the membrane surface that would accept the enterobactin+iron complex.

This also turned out to be the protein that accepted this antibiotic into E. Coli. It appeared that some of the mutations that allowed this were either point or deletion mutations of that protein, either it was deranged or cut off in some location, or outright deleted (missing from the bacteria's set of genes in its DNA).

So this survival mechanism is one of just not letting the antibiotic inside in the first place, which is how it appears teixobactin producing bacteria survive it. They appear to synthesize and expel it, and they don't have cell walls allowing it to get back in.

[danieltillett]

I am a microbiologist. It is not that you want to target basic cell structures, but you want to either target multiple systems, or target systems that have a large number of modular interactions. It is relatively easy to create/discover new chemicals that kill bacteria specifically, but if these new chemicals only target one specific component then the bacteria rapidly evolve resistance. All the good antibiotics we have interact with complex systems like ribosomes that are made up of multiple interacting modules.

The reason we are having trouble finding new classes of antibiotics is that we are already have chemicals that target most of the interacting and essential cellular modules in bacteria. If you already are targeting 90% of all the possible targets you will find it very hard to discover any new classes of antibiotics.

Of course the solution is not to worry too much about finding new classes and just keep tweaking the current antibiotics to keep ahead of the bacteria. The only problem with this strategy is that the economics of antibiotic development is totally broken so the pharmaceutical companies have in the main stopped spending money on finding new antibiotics. What we need to work on is a new way of paying for new antibiotic development.

[DennisP]

It seems strange to me that we're willing to spend trillions of tax dollars on the military, but when it comes to the bacteria that attack us every day, we throw up our hands and just take whatever the free market finds profitable to provide.

[hga]

http://en.wikipedia.org/wiki/Public_good

Plus drugs are one of the very most heavily regulated "free markets" in the US ... and as others have noted, there are laws like the Bayh-Dole Act (https://en.wikipedia.org/wiki/Bayh%E2%80%93Dole_Act) which can make the process much more of a government-non-profit-corporate partnership. There is also a "Generating Antibiotic Incentives Now" (GAIN) in effect, with an bipartisan Antibiotic Development to Advance Patient Treatment in the works.

So, no, we don't "just take whatever the free market finds profitable to provide", where "profitable" has "the visible foot" of the government strongly weighting one side of the balance scale. Not to mention very strong medical policy to restrict new novel antibiotics like this one to the cases where they're really needed.

[danieltillett]

The medical policy is a major component of the problem. What the drug companies have discovered is if they release a new antibiotic that the doctors put it on the shelf with the plan to only use the antibiotic in emergencies. Of course when this happens the drug company makes no money and so rightly concludes that antibiotic development is not profitable.

There have been lots of proposals to overcome this. My personal favourite is each country agrees to pay a straight cash bonus for each new antibiotic developed with a different valued bonus in proportion to the need. The drug companies would then not need to worry if the antibiotic was used or not and we would have on tap new antibiotics to use as resistance arises.