Vinegar has been used as a disinfectant for thousands of years, but new evidence shows that it might also be an inexpensive and effective way to fight the spread of tuberculosis (TB) and other mycobacterial infections.
A new study in mBio this week shows that not only does acetic acid, the active ingredient in vinegar, kill Mycobacterium tuberculosis, but it also kills members of the Mycobacterium abscessus complex, a group of emerging mycobacterial culprits, which can be both antibiotic-resistant and disinfectant-resistant.
“Mycobacteria are known to cause tuberculosis and leprosy, but non-TB mycobacteria are common in the environment, even in tap water, and are resistant to commonly used disinfectants. When they contaminate the sites of surgery or cosmetic procedures, they cause serious infections and can leave deforming scars,” says Howard Takiff, senior author on the study and head of the Laboratory of Molecular Genetics at the Venezuelan Institute of Scientific Investigation (IVIC) in Caracas. These non-TB mycobacteria were behind one of Brazil’s largest outbreaks of post-surgical infections in 2007.
The most effective disinfectants against TB are chlorine bleach, which is toxic and highly corrosive, or commercial disinfectants that can be very expensive. In the resource-poor countries where the majority of TB occurs, Takiff notes, there is a great need for effective, non-toxic, non-corrosive and inexpensive disinfectants.
Vinegar, which fits all of those requirements, has been used as a cleaning agent and medical remedy since ancient times. Recommended for soothing jellyfish stings and treating swimmer’s ear, it is also used widely used to wash produce. Takiff’s postdoctoral fellow, Claudia Cortesia, rediscovered the disinfecting power of acetic acid during a routine experimental control.
Cortesia was investigating drugs that might block the resistance of M. abscessus to commonly used disinfectants. One such drug needed to be dissolved in acetic acid, but when she ran the negative control for the experiment by simply adding the acetic acid solvent to the bacterial culture, she realized that it alone was killing off the pesky M. abscessus.
“This was one of those ‘Huh?’ moments in science,” says Takiff. “Is this an artifact or do we pursue this? Claudia is an unassuming, modest, hard-working and talented scientist. She has this habit of making interesting, unexpected observations and then we work to explain them.”
While on a sabbatical in Laurent Kremer’s lab at University of Montpellier 2 in France, Takiff had the chance to confirm how effective acetic acid was against M. abscessus, “perhaps the most resistant and pathogenic of the non-TB mycobacteria and a frequent cause of infections,” he says. He often stopped at the grocery store on his way to the lab and picked up a liter of white vinegar for less than US$1 for his experiments. He found that mixing the cultures with a 10% acetic acid solution for 30 minutes effectively killed the bacteria, including complex members M. abscessus, M. bolletii, and M. massiliense.
Since neither the Kremer nor the Takiff laboratory was equipped to test TB strains, their collaborators Catherine Vilchèze and William Jacobs, Jr. at the Albert Einstein College of Medicine in New York tested acetic acid’s ability to kill M. tuberculosis strains that were virulent, multidrug resistant (MDR), and extensively drug resistant (XDR). For all three strains, 30 minutes exposure to a solution of 6% acetic acid killed the bacteria, with no survivors remaining.
A 10% acetic acid solution is about twice as strong as vinegar sold in US grocery stores, and the authors calculate that enough acetic acid to disinfect 20 liters worth of TB samples or cultures would cost less than US$100. Takiff notes that even a 25% solution is non-toxic and only a mild irritant if spilled on the skin.
Although the team did not investigate the mechanism of action of acetic acid’s ability to kill mycobacteria, they did show that it is not simply due to the low pH of the solution. Takiff says that the lack of any resistant bacteria to it suggests a generic mechanism, rather than something that depends on one or two specific genes in a pathway.
“We can’t say we discovered something since vinegar’s ability to disinfect has been known since the Roman ages. Two thousand years of uses can’t be all wrong,” says Takiff. “It turns out the disinfectant activity of acetic acid was investigated in the early 20th century and has been studied in the food industry. We observed this interesting effect and extended earlier findings to suggest that vinegar might be worthwhile reconsidering to see if it’s practical and useful in the lab, and maybe even the clinic.”