MIT researchers have discovered a way to make antibiotics more powerful by making bacteria more vulnerable.
The team worked specifically on a class of antibiotics known as quinolones, which include ciprofloxacin and are often used to treat infections such as Escherichia coli and Staphylococcus aureus. The new strategy overcomes a key limitation of these drugs, which is that they often fail against infections that feature a very high density of bacteria. These include many chronic, difficult-to-treat infections, such as Pseudomonas aeruginosa, often found in the lungs of cystic fibrosis patients, and methicillin-resistant Staphylococcus aureus (MRSA).
Bacteria that have become tolerant to a drug enter a physiological state that allows them to evade the drug’s action. (This is different from bacterial resistance, which occurs when microbes acquire genetic mutations that protect them from antibiotics.)
In a study published in 2011, the same researchers behind the latest study had found that they could increase the ability of antibiotics known as aminoglycosides to kill drug-tolerant bacteria by delivering a type of sugar along with the drug. The sugar helps to boost the metabolism of the bacteria, making it more likely that the microbes will undergo cell death in response to the DNA damage caused by the antibiotic.
However, aminoglycosides can have serious side effects, so they are not widely used. In their new study, Collins and his colleagues decided to explore whether they could use a similar approach to boost the effectiveness of quinolones, a class of antibiotics used more often than aminoglycosides. Quinolones work by interfering with bacterial enzymes called topoisomerases, which help with DNA replication and repair.
With quinolones, the researchers found that it wasn’t enough to add just sugar; they also had to add a type of molecule known as a terminal electron acceptor. Electron acceptors play an essential role in cellular respiration, the process that bacteria use to extract energy from sugar. In cells, the electron acceptor is usually oxygen, but other molecules, including fumarate, an acidic organic compound that is used as a food additive, can also be used.
In tests in high-density bacterial colonies grown in a lab dish, the researchers found that delivering quinolones along with glucose and fumarate could eliminate several types of bacteria, including Pseudomonas aeruginosa, Staphylococcus aureus, and Mycobacterium smegmatis, a close relative of the bacterium that causes tuberculosis.
The findings suggest that high-density bacterial infections rapidly consume nutrients and oxygen from their environment, which then provokes them to enter a starvation state that helps them to survive. In this state, they greatly reduce their metabolic activity, which allows them to avoid the cell death pathway that is normally triggered when DNA is damaged by antibiotics.