Can Salted Doorknobs Prevent Superbug Infections?
In the battle against antibiotic resistance, salt might be a simple but effective weapon.
Over the last millennium, salt has undergone a major status shift, from exotic delicacy that drove humans to war to kitchen condiment taken so for granted that 90 percent of Americans consume too much of it without even trying. But new research suggests that salt may be on the verge of yet another reinvention—this time in the world of disease control.
Superbugs like Methicillin-resistant Staphylococcus aureus, or MRSA, have wreaked havoc on the health-care system in recent years. Drug-resistant infections, which include superbugs, are responsible for more than 700,000 deaths globally each year, and come with an approximate annual cost of $20 billion in the United States alone. How do you stop them? Frequent hand washing is one option, but that requires a behavior change, which can be difficult, even for hospital staff. Another option is to coat those frequently fondled objects most likely to carry the bugs—doorknobs, bed rails, toilet handles—with a special anti-microbial surface, like copper. This approach is increasingly popular, but time is of the essence when it comes to preventing the spread of disease, and MRSA has been shown to survive even on copper for several hours.
Who knew salt could be up for the job? Well, butchers, for one, who have used it to fight off pathogens like Salmonella for centuries. And it was a casual conversation with a former butcher that led Brayden Whitlock, a graduate student at the University of Alberta, to design a pilot study that put salt and copper head to head. Coupon-sized strips of pure, compressed sodium chloride were covered in an MRSA culture, alongside similar strips of antimicrobial copper and stainless steel. Whitlock found that salt killed off the bug 20 to 30 times faster than the copper did, reducing MRSA levels by 85 percent after 20 seconds, and by 94 percent after a minute.
That was “considerably faster” than expected, Whitlock says—and he believes this efficiency could have major ramifications for how bugs like MRSA spread. “It’s great to be able to eliminate pathogens over the course of a few hours,” he says, “but if you think of a busy place that has a doorknob, or a push pad, can you imagine a time when it goes more than a few minutes without being touched? The answer to us is no. And that’s why this is really exciting.”
Meanwhile, fellow researchers at the University of Alberta have found another potential medical use for salt: this time, as a coating on surgical masks. These masks are designed to trap viruses that wearers are carrying, like influenza, but need to be thrown away after a single use. A paper co-authored by Hyo-Jick Choi, an assistant professor of chemical and materials engineering, found that soaking the inner membrane of a common surgical mask in a solution of sodium chloride made the mask actually able to destroy the flu virus outright, which could allow for multiple uses.
Influenza is carried via droplets that the wearer exhales into the membrane, and “when the water evaporates, salt ions gather to form crystals,” says Choi. “The crystals look like a very sharp spearhead. So they easily kill the virus.”
Choi’s primary area of research is in vaccines and pandemic preparedness, and that’s where he sees the masks’ biggest potential. During an influenza outbreak, he says, it takes scientists a minimum of six months from the time the strain is identified to the production of a vaccine; meanwhile, the MERS virus spread across South Korea in a matter of weeks in 2015. It’s in this interim period, between outbreak and vaccine, that many people don surgical masks in an attempt to protect themselves and others, but doing so can backfire if the masks are worn too long or handled incorrectly. In addition to appearing safe for reuse, the masks Choi is hoping to develop are equally effective at killing all types of influenza, because they rely on a physical process. Salt has the added advantage of being stable across most environments, easy to handle, and cheap to acquire.
Choi’s masks are, however, still vulnerable to average human error—specifically, maintaining that critical seal around the mouth and nose. “It’s really hard to wear a mask all day long,” says Pedro Piedra, a professor in molecular virology and microbiology at the Baylor College of Medicine in Houston, Texas. “You could have a system that truly improves the filtration and the inactivation of the virus, in a very affordable way, but if you’re just wearing a surgical mask, you still have the same issues: It’s still not fitted, it’s still loose, and so aerosols can potentially get in or get out.” More research is also needed to ensure that breathability isn’t an issue through the added layer of salt.
The salt-covered doorknobs, meanwhile, are already in the market. Doug Olson, the former butcher who first told Whitlock about the idea, has already received a patent for the technology in nine different countries, and registered the trade name Outbreaker. Prototypes have been built by local salt companies—the compression process is identical to how salt licks for livestock are made—and discreetly installed in a handful of settings around Edmonton, Alberta’s capital, over the past few years. Compressed and smooth, with a feel akin to ceramics, Whitlock says most users have no idea that what they’re really grabbing is a fistful of table salt.