Products containing the antibacterial chemical triclosan have had a bad press lately because of fears that they may promote antibiotic-resistant bacteria. A trip to the supermarket suggests that triclosan may have been given a worse name than it deserves, say scientists from the University of Manchester in Britain.

Peter Gilbert and his colleagues found that 15 out of 23 products selected at random from the shelves of their local supermarket could select for resistant bacteria in the same way that triclosan does.

"Bacteria have evolved to cope with natural antibacterials in the environment," Gilbert told the annual meeting of the American Society for Microbiology in Orlando, Florida. Shower gel, mustard and cinnamon flipped the same molecular defence switch in bacteria that triclosan does. Fenugreek, pasta sauce and white wine had little effect.

Triclosan interferes with an enzyme crucial to the growth of bacteria. But it also trips a genetic master switch called the multiple antibiotic resistance (mar) operon. This activates a pump in the bacterial cell wall that expels a host of unwanted chemicals. "It's a bacterium's vomit response," explains Gilbert.

So, by setting the pump running, triclosan can help bacteria spew out antibiotics, warns antibacterial critic Stuart Levy of Tufts University School of Medicine in Boston, Massachusetts. If the stimulus is strong enough, Levy says, compounds such as triclosan can leave us with bacteria whose pumps are running constantly.

But triclosan isn't the only compound that can turn bacteria into "permanent vomitors", Gilbert argues.

Using a strain of Escherichia coli genetically modified to stain a different colour when their mar operons were on, Gilbert found that half of his random shopping-list could stimulate the efflux receptor. Six of them did so more powerfully than triclosan.

Gilbert doesn't advocate the use of antimicrobials in situations where there is no benefit. But he makes the point that antibacterial critics "could end up throwing the baby out with the bath water", depriving consumers of a potentially useful product.

Triclosan opponents such as Levy are unconvinced. "I don't see a health relevance to his findings," he says, adding that the point is that antibacterial products are being widely used in homes, "with consumer expectation being that they're a benefit. That benefit hasn't been shown but what has been shown is that there's a risk."