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Bacteria find it difficult to evolve antibiotic resistance when in a community

Updated: Feb 13, 2020

Community living may force bacteria to develop antibiotic resistance more slowly finds a study from the UK and Chinese researchers by testing how bacteria react to antibiotics when thriving as a part of the community.

Antibiotic resistance has been a bane to human society and a global threat to public health ever since they were commercially introduced. Germs have always found a way to develop resistance to all the antibiotics discovered by humankind.

However, drug resistance has always been studied with single pure cultures in the lab. However, bacteria in nature, live in a complex community, just like us, or any other living being. It is somewhat relieving to know that it is harder for the bacteria to develop resistance living with other microbes in a complex community nature, than in single isolated cultures.

"We show that selection for antimicrobial resistance was influenced by being embed in a 'natural' microbial community, such that the minimum selective concentration (of antibiotics) was increased by more than one order of magnitude for two different antibiotics," says Dr. Uli Klumper, the lead author of the paper published in the ISME journal on August this year.

The study has special relevance because bacteria live as a community in our gut too. The authors, therefore, advise the doctors to prescribe an antibiotic that is narrow in its range of action, i.e., which kills specifically only a particular bacteria and therefore retains the rest of the community. The rest of the bacteria, now because they are a part of the still-thriving community, will have a hard time developing resistance to the administered antibiotic!

Testing with two antibiotics Gentamycin and Kannanycin on Escherichia coli, a bacteria that is commonly used in Labs, and borrowing a community of bacteria from pig fecal matter, the researchers set up experiments that mimic semi-natural states in fermenters.

They tested how well each of the bacteria was doing in different concentrations of the two antibiotics and noted the concentrations at which antibiotic resistance develops. They found that it took E. coli a higher concentration of the antibiotics to develop resistance when they were a part of the community compared to when they were pure cultures.

"There was a small competitive fitness cost of Gentamycin resistance in the absence of the community, and this cost appeared to be greatly increased when the community was present," says Dr. Uli Klumper. Imagine that you are a vendor in a very competitive market, and you compete for space, resources, and profit. If there is an additional pressure imposed on you like an unexpected tax, you probably will lose the competitive edge trying to compromise. On the other hand, if you are the sole vendor and there is no competition from the rest, you could probably cope better with any challenge.

Likewise, it takes less concentration of the antibiotic for a pure culture to develop resistance when it is growing alone. However, in the context of a community that surrounds you day and night, resistance development is a costly affair that you can afford only when it reaches a higher and critical concentration.

"For Gentamycin, the community increased the fitness costs reflected by reduced growth rates that are associated with resistance in the absence of antibiotics," says Dr. Uli Klumper. Therefore, developing resistance requires a higher cost and only resorted to when the concentrations of the antibiotic become critical and unbearable.

- written by Manohar G M

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