Benzalkonium Chloride Promotes Antibiotic Resistance
    By News Staff | December 28th 2009 12:00 AM | 7 comments | Print | E-mail | Track Comments
    Bacteria exposed to a common disinfectant called benzalkonium chloride may develop resistance to certain antibiotics as well as the disinfectant itself, according to research published in the January issue of Microbiology. The authors of the study say their findings could have important implications for how the spread of infection is managed in hospital settings.

    Researchers from the National University of Ireland in Galway found that by adding increasing amounts of disinfectant to laboratory cultures of Pseudomonas aeruginosa, the bacteria could adapt to survive not only the disinfectant but also ciprofloxacin - a commonly-prescribed antibiotic - even without being exposed to it. The researchers showed that the bacteria had adapted to more efficiently pump out antimicrobial agents (disinfectant and antibiotic) from the bacterial cell. The adapted bacteria also had a mutation in their DNA that allowed them to resist ciprofloxacin-type antibiotics specifically.

    Importantly, the study showed that when very small non-lethal amounts of disinfectant were added to the bacteria in culture, the adapted bacteria were more likely to survive compared to the non-adapted bacteria. Dr. Gerard Fleming, who led the study, said, "In principle this means that residue from incorrectly diluted disinfectants left on hospital surfaces could promote the growth of antibiotic-resistant bacteria. What is more worrying is that bacteria seem to be able to adapt to resist antibiotics without even being exposed to them."

    P. aeruginosa is an opportunistic bacterium that can cause a wide range of infections in people with weak immune systems and those with diseases such as cystic fibrosis (CF) and diabetes. P. aeruginosa is an important cause of hospital-acquired infections. Disinfectants
    are used to kill bacteria on surfaces to prevent their spread. If the bacteria manage to survive and go on to infect patients, antibiotics are used to treat them. Bacteria that can resist both these control points may be a serious threat to hospital patients.

    The researchers also stressed the importance of studying the environmental factors that might promote antibiotic resistance. "We need to investigate the effects of using more than one type of disinfectant on promoting antibiotic-resistant strains. This will increase the effectiveness of both our first and second lines of defence against hospital-acquired infections," he said.

    : Paul H. Mc Cay, Alain A. Ocampo-Sosa, Gerard T. A. Fleming, 'Effect of subinhibitory concentrations of benzalkonium chloride on the competitiveness of Pseudomonas aeruginosa grown in continuous culture', Microbiology Jan. 2010, 30-38; doi  10.1099/mic.0.029751-0


    Do you ever get the feeling that the cards are stacked against us and that we're fighting a losing battle? It just seems that microorganisms like bacteria are the most adaptable lifeforms on the face of the Earth.
    Gerhard Adam
    It seems that we perpetually overlook the fact that the world (and biosphere) are dynamic entities and they don't remain static simply because we wish them to.

    Just like we can't hold the climate fixed, nor can we ensure that the Grand Canyon doesn't eventually disappear, neither can we presume that other biological organisms will simply remain fixed in time while we deal with them.

    It isn't so much that the deck is stacked against us, it's just that we keep thinking that we can circumvent natural selection.
    Mundus vult decipi
    I realize that, Gerhard. It's just sometimes from a human perspective it all seems kind of pointless. I'm speaking more philosophically here than scientifically. When I was in college taking organic chemistry and studying viri I had a mixed reaction. On the one hand, I marveled at how such a simple little machine could be such a quintessential instantiation of survival. But at the same time, I was horrified how insidiously these machines worked and how quickly they could mutate.

    It seems for the whole history of this planet it has been one big arms race, with each species pitted against another with ultimately no winners. One has to wonder if Voltaire was not right when he said, "God is comedian playing to an audience afraid to laugh." It just seems sometimes that we are a source of amusement for some sadistic, malevolent being who derives pleasure at our expense.
    Gerhard Adam
    True enough.  My comments were more a reflection of the fact that it seems we're perpetually in a struggle to stop the world while it continues on its way regardless of our efforts.

    When I hear medical researchers talking about correcting all manner of ills, I'm still struck by the naivete that seems to neglect the fact that something else will emerge to draw our attention.  It certainly doesn't mean that we should become fatalistic, but similarly we should stop with the unbridled optimism too.
    Mundus vult decipi
    I couldn't agree more, Gerhard! ;-)
    Gerhard Adam
    I often wonder what direction things could take if we simply shifted our perspective and moved research along different paths.  Just speculating, but consider if instead of developing stronger antibiotics, we focused research on bolstering our immune system's responsiveness.

    Don't get me wrong, I fully realize that such an endeavor is hardly trivial, but it does open up some interesting speculations about how we might go about solving problems differently if we didn't take such an adversarial approach to things.
    Mundus vult decipi
    I think that in and of itself could become a Pandora's box. I just don't think we understand enough about genetics, epigenetics and protein folding in the human body to where we could be sure that we wouldn't create something worse than the diseases we're battling.

    It seems to me that a part of the problem is of our own making. We use disinfectants like  benzalkonium chloride and chlorine excessively and almost exclusively, thus allowing microbes time to evolve into more resistant and virulent strains. We have a bad habit of putting all of our eggs in one basket when we discover something that is extremely effective. There are other disinfectants both for medical procedures as well as for the cleaning of surfaces. Perhaps a regimen of rotating the use of different disinfectants would at least slow down the progress of these organisms mutating and becoming resistant.

    We also have contributed to the problem by the overuse of antibiotics, again giving bacteria time to evolve into resistant strains.

    A large number of pathogens that have become a serious threat to public health are not necessarily new bugs but rather new strains of old ones coming back with a vengeance (e.g. a strain of tuberculosis that is resistant to every antibiotic except one which has to be administered intravenously).

    Even new pathogens such as the H1N5 influenza virus have unhealthy and unsanitary human practices behind them. This virus is believed to have gotten its start in southeast Asia from 1) people in the countries there eating undercooked sick poultry and 2) the unhealthy cultural practice of owners licking the blood off of the heads of their roosters after a cock-fight.

    So, unless we get people to change some of their ways, I'm afraid the creation of new and more virulent strains of old bugs is going to continue.