Antibiotics May Increase Bacterial Growth


Doxycycline was seen to mutate E. coli in a way that leads to producing colonies 3 times larger.

While antibiotics are used to kill bacteria and fight infections, investigators have found that antibiotic use may actually stimulate bacterial growth.

In a new study published by Nature, Ecology & Evolution, Escherichia Coli that was exposed to 8 rounds of antibiotics over 4 days increased resistance with each treatment.

Increased resistance was expected, but the investigators also discovered that the bacteria grew faster after antibiotic treatment compared with before. Mutated E. coli was observed to create populations 3 times larger than pre-treatment bacteria.

These changes were only observed among bacteria exposed to antibiotic treatment. When the drugs were removed, the mutations and new abilities of the bacteria remained, according to the study.

“Our research suggests there could be added benefits for E. coli bacteria when they evolve resistance to clinical levels of antibiotics,” said lead author Robert Beardmore, PhD. “It’s often said that Darwinian evolution is slow, but nothing could be further from the truth, particularly when bacteria are exposed to antibiotics. Bacteria have a remarkable ability to rearrange their DNA and this can stop drugs working, sometimes in a matter of days. While rapid DNA change can be dangerous to a human cell, to a bacterium like E. coli it can have multiple benefits, provided they hit on the right changes.”

In the study, the authors used doxycycline on the bacteria, and then froze it at -80C. Then, they used genetic sequences to observe the DNA changes responsible for the mutations, according to the study.

Changes, such as the bacteria producing more antibiotic pumps to push the drugs out of the cell, have been seen in real-world situations. Other changes, such as losing DNA to become a dormant virus, were never seen before.

“Our best guess is that losing viral DNA stops the E. coli destroying itself, so we see more bacterial cells growing once the increase in pump DNA allows them to resist the antibiotic in the first place,” said researcher Carlos Reding, PhD. “This creates an evolutionary force for change on two regions of the E. coli genome.”

These findings are significant because the prevalence of antibiotic-resistant bacteria are increasing, with some patients developing life-threatening infections. Due to the role of antibiotics in creating these bacteria, many institutions have restricted use of the drugs.

Other initiatives have increased physician education about antibiotic resistance, and giving physicians feedback regarding their prescribing habits.

“It is said by some that drug resistance evolution doesn’t take place at high dosages but our paper shows that it can and that bacteria can change in ways that would not be beneficial for the treatment of certain types of infection,” said researcher Mark Hewlett, PhD. “This shows it’s important to use the right antibiotic on patients as soon as possible so we don’t see adaptations like these in the clinic.”

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