This is scary and complex.....
THE widespread use of antibiotics encourages the pathogens they are directed against to become inured to their effects. That is well known. But antibiotics cause damage to non-target species as well, so these, too, tend to evolve immunity. Since most antibiotics are administered by mouth, the many bacteria that live peacefully in the human gut are particularly susceptible to such evolutionary pressures.
The medical consequences of this are ill-understood, in part because most gut bacteria are anaerobes (meaning they flourish only in the absence of oxygen) and so are difficult to culture. But Lisa Maier of the European Molecular Biology Laboratory, in Heidelberg, and her colleagues have, nevertheless, grown 40 of the most common strains of them in anaerobic conditions. They have then gone on to expose those cultures to hundreds of drugs for a range of ailments, at the sorts of concentrations that might be encountered in the human intestine. Their study, published this week in Nature, has revealed an unexpected avenue by which gut bacteria can become resistant to antibiotics: exposure to drugs that were designed to act on human cells rather than microbial ones.
Of the drugs in the study, 156 were antibacterials (144 antibiotics and 12 antiseptics). But a further 835, such as painkillers and blood-pressure pills, were not intended to harm bacteria. Yet almost a quarter (203) did. These accidental bactericides included proton-pump inhibitors such as omeprazole (used to treat acid reflux), calcium-channel blockers (to lower blood pressure), antihistamines, painkillers and antipsychotics. (In the case of antipsychotics, these chemically diverse drugs seemed to affect many of the same strains of gut bacteria. That suggests their effects on the brain could, in part, be a result of their influence on gut flora).
The researchers noticed too that the strains of bacteria most resistant to the effects of drugs not aimed at them were also those most resistant to antibiotics. This observation implied that these bacteria were using similar means to defend themselves against both sorts of medicine.