New microbiota-based mode of antibiotic-resistant spread identified.

Bacteria are becoming increasingly resistant to antibiotics, with much work needed to stem the rise of multi-drug resistance. Often, resistance is mediated by genes, which can simply jump from one bacterial population to the next when antibiotics are being used. This is one of the many mechanisms of antibiotic resistance which is causing major concern around the world. Now, a study from researchers led by ETH Zurich identifies an additional, previously unknown mechanism which spreads resistance in the intestinal microbiota that is independent of the use of antibiotics. The team state that restricting the use of antibiotics, which is an important facet in the fight against antibiotic resistance, is not sufficient to prevent the spread. The opensource study is published in the journal Nature.

Previous studies show the DNA of bacteria is contained in a single circular molecule, called the bacterial chromosome. In addition to the chromosome, bacteria often contain plasmids, small circular DNA molecules which the microbes can pick up from other bacterial cells during conjugation or the environment. Plasmids often carry multiple antibiotic resistance genes, contributing to the spread of multi-drug resistance. It is a long held theory that the global spread of antibiotic resistant plasmids is fuelled by antibiotic usage in human and veterinary medicine. The current study shows that these bacterial plasmids transfer antibiotic resistant genes to both same and different bacterial species without the use of antibiotics.

The current study utilises mice to demonstrate that dormant salmonella, which can form persistent phenotypes of bacteria, can pass their resistance genes in the gut on to other same species bacteria or different species, such as E. coli from the normal intestinal flora. Results show that persistent bacteria or ‘persisters’, subpopulations of bacteria which survive antibiotics by reversibly adapting their physiology, are very efficient at sharing their resistance plasmid genes as soon as they awaken from their dormant state and encounter other bacteria that are susceptible to gene transfer.

The lab explain that by exploiting their dormant persistent host bacterium in reservoirs, the resistance plasmids can survive for a prolonged period in one host before transferring into other bacteria. They go on to add that this speeds up the spread of multi-drug resistant plasmids, they stress that this transfer happens regardless of whether antibiotics are present or not. The group suggests that vaccination reduces the formation of reservoirs of persistent salmonella bacteria phenotype, as well as subsequent plasmid transfer.

The team surmise they have shown that microbiota can pass on multi-drug resistant genes without the presence of antibiotics. For the future, the researchers state they now plan to investigate whether it’s possible to control the spread of resistance in livestock populations with probiotics or with a vaccination against salmonella.

Source: ETH Zurich

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