Microbes and resistance

Tara C. Smith over from Aetiology discusses another example of bacteria developing resistance to new forms of antibiotics. In this case, researchers planned to use small peptides that are found in the immune systems of many organisms (including us) as novel antibiotics. Unfortunately, one of the researchers had a somewhat overconfident idea that bacteria would not be able to develop resistance against these peptides. Thankfully he was challenged on it and found that indeed, resistance would develop in these bacteria if they were exposed.

This was the question asked in a new study by Dr. Zasloff along with colleagues Gabriel Perron and Graham Bell. Following publication of his 2002 paper where he called evolution of resistance to these peptides “improbable,” Bell challenged Zasloff to test this theory. Zasloff took him up on the offer, and they’ve published their results in Proceedings of the Royal Society.

As I alluded to above, the result was the clear development of resistance to the peptides. So much for improbable I guess. What intrigues me is that it was already understood that resistance had already emerged in several bacterial pathogens previously. As T. Smith notes;

For example, resistance to antimicrobial peptides has been shown to be essential for virulence in Staphylococcus aureus and Salmonella species, but we didn't *witness* that resistance develop--therefore, it might simply be that those species have physiological properties that render them naturally resistant to many of these peptides, and were never susceptible in the first place.

I think one of the first examples of resistance was Salmonella enterica serovar typhimurium which is resistant to several antimicrobial peptides. I'm not sure why anyone would have been so confident to think that bacteria wouldn't develop resistance. If some organism had done it in the past (like Salmonella spp) you can almost be certain of them doing it agian. In fact, that would be one of the sorts of tests you could use in the whole ID vs. evolution 'controversy'. If bacteria could not develop some form of resistance again against a new antibiotic, when other species had in the past it would indicate there was something incredibly special or unusual about the previous resistance development. Evolutionary theory would very much predict the redevelopment of resistance even in a completely new species. This development doesn't have to be the same kind of resistance determinant of course, much like if you replayed evolution again flight might evolve in an entirely different way the second time.

Additionally, I think a lot of medical bacteriologists could use some of E. O. Wilsons thinking and fast. It's becoming very clear that individual bacterial species are irrelevant in the big game of evolution. The whole entire 'genome' of the population of bacteria in an area are more critical. If one organism has a mechanism for resistance against an antibiotic, it puts massive selection pressures on plasmids, bacteriophages and other roving DNA elements to aquire it. Quite frankly, I wonder how easily the existing resistance genes could start spreading under selection. It's too dangerous to consider bacteria just having to develop resistance because many of them probably won't. The simple reason is they won't have to, they can grab it from a friend instead.

That is scarier to me. Not the concept of one organism developing resistance, but one organism either having it to begin with or producing a new mechanism and then spreading it around to all of its friends.