Microbes thrive on drugs designed to kill them
Scientists in the US have found that soil is full of bacteria that will feed and grow on antibiotics - the very compounds created to kill them.
Some bacteria are known to munch on toxic compounds such as wood preservative; others thrive in radioactive waste. But now Gautam Dantas, Morten Sommer and their coworkers at Harvard Medical School in Cambridge, Massachusetts, have isolated hundreds of bacterial species from 11 different kinds of soil that not only seem entirely unbothered by antibiotics but will actually ’eat’ them as a carbon source, if there is nothing else on offer.
The researchers exposed the soil bacteria to 18 common natural and synthetic antibiotics, and found that all were consumed by some of the bugs. More than half of the antibiotic-metabolizing species were either Burkholderiales or Pseudomonadales - already known to have versatile metabolic mechanisms and high antibiotic resistance.
The soil samples were taken from many different places including public parks and farms, pristine forest, and land treated with wastewater.
’The increase of multiple-antibiotic resistance in human pathogens is continuingly weakening our ability to fight infectious disease, and any accessible reservoir of resistance mechanisms that could transfer to pathogens could exacerbate the problem,’ say Dantas and Sommer.
So far, the researchers haven’t found any known human pathogens among their antibiotic-consuming organisms, but they say that some are closely related species. This might make it rather easy for pathogens to acquire antibiotic-resistance and antibiotic-metabolising genes from innocuous bacteria.
’However, we think there are some silver linings,’ the two say. ’While many health problems are discovered only when they are close to or beyond a critical tipping point, our findings offer an opportunity to enact solutions to curb the spread of antibiotic-metabolising pathogens before they get out of hand, through more prudent use of antibiotics in medicine and agriculture.’
They add that by figuring out the genetic and biochemical mechanisms involved in metabolizing antibiotics, it might be possible to genetically engineer microorganisms to clean up environments that have been polluted by over-use of antibiotics.
In separate work, Anders N??r of the Massachusetts General Hospital Cancer Center in Charlestown and his colleagues have opened a new window on a different form of pathogenic drug resistance - not in bacteria, but in fungi.
Fungi such as Candida glabrata can cause potentially lethal infections in people with weak immune systems such as AIDS sufferers and cancer patients. But exactly how some fungi manage to evade drugs used to fight them is not known.
Some antifungal drug resistance stems from the activation of genes encoding proteins that help to pump the drugs out of cells. Now N??r’s team have found that transcription factors called Pdr1p and Pdr3p get switched on when the drugs stick to a water-repelling part of these proteins, and that this can enable the transcription factors to turn on the production of drug-clearing machinery. Identifying this molecular mechanism could point the way to the design of other drugs that block it.
1 G Dantas et al, Science, 320, 100, 2008 (DOI: 10.1126/science.1155157)
2 J K Thakur et al, Nature, 452, 604; 2008 (DOI: 10.1038/nature06836)