Salmonella causes diarrhea in animals and humans. These bacteria become a particular public health concern if they are resistant to antibiotics (electron microscopic photograph). Source: ETH Zurich / Stefan FattingerAccording to the CDC, antibiotic resistance is one of the world's biggest public health challenges. At least two million people in the U.S. alone contract an antibiotic-resistant infection and at least 23,000 of those infected die each year.

Since the advent of penicillin, antibiotic resistance has developed alongside the introduction of antibiotics and a common assumption has been that the presence of antibiotics is necessary for resistance to develop. However, scientists from ETH Zurich and the University of Basel have discovered an additional mechanism independent of the use of antibiotics that spreads resistance in intestinal bacteria. The researchers found that controlling the spread of the resistant microorganisms through more effective hygiene and vaccinations, along with restricting the use of antibiotics, is key to preventing the spread of resistance.

[Read Chips, sensors and lasers used to study antibiotic-resistant bacteria and Ingredient found in certain hand washes and toothpastes may contribute to antibiotic resistance to learn about other efforts to curb the spread of antibiotic and antimicrobial resistance.]

The researchers experimented with mice and were able to demonstrate that dormant salmonella in the gut passes resistance genes to other bacteria both of the same species and also to other species, such as E. coli. Persistent bacteria, known as persisters, can temporarily become dormant and in this state can survive antibiotic treatment by minimizing their metabolism. The persisters can survive this way for months. Once they awaken, in the right conditions, the infection can resurface.

Upon awakening, the persisters are quite efficient at sharing their resistance genes with other bacteria that are susceptible to gene transfer. "By exploiting their persistent host bacterium, the resistance plasmids [small DNA molecules] can survive for a prolonged period in one host before transferring into other bacteria. This speeds up their spread," explained Wolf-Dietrich Hardt, professor of microbiology at ETH Zurich. This transfer happens even when antibiotics are not present.

The researches plan to expand their study to livestock, such as pigs, which are frequently impacted by salmonella infections and to determine the possibility of using probiotics or vaccination against salmonella to control the spread of resistance in livestock populations.

The report on this research appears in the journal Nature.