Bacteria can easily acquire genes from other microbes, and many times these shared genes enable the microbes to evade the effects of an antibiotic. For many reasons, including the overuse and misuse of antibiotics, there are ever-increasing numbers of antibiotic-resistant bacteria, which could pose a major threat to public health in the coming years.
Researchers have now discovered a novel resistance gene that allows bacteria to resist the impacts of an aminoglycoside antibiotic called plazomycin. Aminoglycoside medications are used to treat several kinds of multidrug-resistant infections and work by preventing microbes from making new proteins.
In this study, which was reported in Microbiome, the researchers turned to the environment to look for resistance genes. In our world, there are untold numbers of microbes that all have to compete for resources. That means that many bacteria produce their own antibiotics to fight off other microbes, and bacteria can, in turn, produce antibiotics so that they can rise to meet the challenge posed by their microbial foe. These natural antibiotics have been called the resistome.
After identifying a resistance gene in samples of river sediment from India, the scientists compared the sequence of this gene to reported bacterial sequences. They found that this gene was already present in the genomes of several potentially infectious microbes, including Salmonella and Pseudomonas strains from the United States, Italy, and China. Researchers had not known that this gene conferred resistance to an antibiotic until now.
"Early discovery of resistance genes can help us managing their spread, facilitate gene-based diagnostics and perhaps also guide industry to develop drugs that can circumvent the resistance," said the senior study author Professor Joakim Larsson, director of the Centre for Antibiotic Resistance Research at University of Gothenburg, Sweden.
The researchers found that the gene enables bacteria to resist antibiotics that have a chemical group called garosamine, an amino monosaccharide, which includes the newest type of aminoglycoside medicine. This drug was created to supplement aminoglycosides that bacteria have become resistant to. The scientists named the gene gar.
"It is good news that the gar gene still seems to be rather rare, but as it is spreading, it will likely further complicate treatment of already multi-resistant bacteria. Pseudomonas aeruginosa, for example, is a common cause of hospital-acquired pneumonia," said Larsson. "Being able to treat secondary bacterial lung infections is something that we are particularly worried about these days when the world is hit by the COVID-19 pandemic."
Just as microbes are racing to develop better tools in their own arms race, humans also have to stay vigilant. As we develop new antibiotics, it's likely that even when used responsibly, bacteria will eventually find a way to get around them.
"Every antibiotic mankind has developed so far has eventually been met by resistance in at least some of the pathogens it was intended to treat. The gar gene is just the latest in a series of genes that one by one reduces the value of antibiotics," noted Larsson.
"The enormous diversity of bacteria in the environment around us probably already harbor genes to every antibiotic we ever will develop -- unless we start thinking very differently about how antibiotics are designed," Larsson added.