Genes that allow bacteria to beat antibiotic treatments can be passed between species with ease, say scientists.
Bacteria such as Salmonella can become tougher
Our natural gut bacteria may have acquired antibiotic resistance, but they can hand that advantage to less friendly strains.
Researchers at the Rowett Research Institute in Aberdeen found that genes which conferred resistance against the antibiotic tetracycline transferred easily between gut bacteria and disease-causing bugs.
Dr Karen Scott, who will present this evidence on Monday at the Society for General Microbiology Spring Meeting in Edinburgh, said: "We all have a huge number of different bacteria in our guts.
Any of these bacteria can readily transfer genes to each other which give resistance to some of our most important antibiotics.
Dr Karen Scott, Rowett Research Institute
"Between them they make up a reservoir of millions of genes which they can exchange with each other.
"Some of the bacteria are harmless - such as the bacteria in live yoghurt, and can live safely with us all the time.
"But others, such as Salmonella, may make us very ill. Any of these bacteria can readily transfer genes to each other which give resistance to some of our most important antibiotics."
The problem of antibiotic resistance is growing.
In recent years there have been outbreaks of bacteria resistant to all but a handful of modern antibiotics.
These have mostly been confined to hospitals, where drug-resistant bugs are more likely to arise.
Researchers have found that genes conferring antibiotic resistant are far more likely to be swapped between strains if they are carried on a particular part of the bacterium's DNA.
These parts, called a plasmid or "tranposon", can be easily exchanged by different bacteria in close contact with each other.
The Rowett team believes its findings on gene transfers could help scientists come up with ways to prevent this happening so often.
Dr Scott said: "Once we know more about the way these genes are passed on, we will be able to help doctors minimise the risk from spreading antibiotic resistance, and improve the way our current antibiotics are used."