Picking up where traditional antibiotics are failing, two natural compounds have been shown effective in killing antibiotic-resistant bacteria in wastewater. The finding could point towards a natural way to defeat the increasingly undefeatable bugs.
While much of the focus on antibiotic resistant bacteria has been fighting them inside our bodies where they can cause everything from tuberculosis to urinary tract infections, another problematic locus for the so-called superbugs is in our wastewater. Because antibiotics are excreted by humans and animals taking them to treat or ward off infections, they regularly find their way into wastewater. Once there, the bacteria that’s also present in the water can evolve to resist the effects of the drugs, morphing into organisms against which even our strongest antibiotics can fail.
Seeking a solution to the issue of a superbug surge in wastewater, American and Chinese scientists led by Utah State University (USU) turned their attention to natural compounds. Because treated wastewater can wind up back in the water table, using natural solutions to fight the bugs can help keep potentially harmful chemicals out of the environment.
They tested 11 natural compounds in all and found two powerful bug-busting winners: emodin from rhubarb and curcumin from turmeric.
“We selected a panel of compounds primarily derived from plants, such as curcumin from turmeric, quercetin from onions and apples, and emodin from rhubarb,” said senior study author Liyuan ‘Joanna’ Hou of USU. “These compounds were chosen based on their reported antimicrobial or anti-biofilm properties in previous studies and their natural abundance, making them promising candidates for exploring new, environmentally friendly approaches to mitigate resistance.”
In particular, they found that both emodin and curcumin were able to inhibit the production of biofilms, colonies of bacteria that group together for protection and are much harder to kill than individual bugs. They also discovered that curcumin combined with a high dose of emodin was able to reduce cellular activity in the bugs.
In reaching their conclusions, the researchers isolated nine different strains of bacteria that were shown to be resistant to the antibiotic sulfamethoxazole. These strains included species of Microbacterium, Chryseobacterium, Lactococcus lactis, and Psychrobacter. On their own, these species aren’t usually dangerous to people, however they can cause opportunistic infections in those with lowered immune systems. Plus, if they are allowed to thrive in wastewater, they could potentially pass along their antibiotic-resistant genes to other more dangerous species.
Of fruits and fungus
Next, the team tested the effects of compounds taken from a range of natural sources on the bugs: berberine, found in goldenseal and barberry; chlorflavonin found in the fungus aspergillus candidus; chrysin found in honey; curcumin from turmeric; emodin from rhubarb, hesperidin, naringin, and rutin, found in citrus fruits; quercetin, found in a range of fruits and vegetables; resveratrol, found in grapes; and 2’-hydroxyflavone, found in multiple fruits, vegetables, and herbs.
While the rhubarb- and turmeric-based compounds were the only ones shown to be effective, the researchers point out that they only worked against gram-positive bacteria. The more resistant strains of gram-negative bacteria, such as E. coli and Salmonella, did not succumb to any of the natural treatments.
“While natural compounds like curcumin and emodin show promise in inhibiting Gram-positive multidrug-resistant bacteria, further research is needed,” said Hou. “Future work should include testing these compounds in complex wastewater matrices, exploring synergistic effects with existing treatment processes, and assessing long-term impacts on microbial communities and resistance dynamics. Additionally, scaling up from laboratory studies to pilot-scale trials will be critical for evaluating feasibility and environmental safety.”
The research has been published in the journal Frontiers in Microbiology.
Source: Utah State University via Scimex
