Remnants of everything that humans ingest ends up in wastewater, including medications that people may be taking, like antibiotics. Low levels of antibiotics in wastewater can affect bacteria as well, by exposing them to those antibiotics, and giving bacteria a chance to develop resistance. Wastewater can also provide researchers with an opportunity to study interactions between bacteria, antibiotics, and other molecules.
Scientists have now identified bacterial species in wastewater that are harboring antibiotic resistance genes. While these bacteria are not usually threatening to people, they could pass those resistance genes onto other bacterial pathogens that are dangerous.
The investigators also isolated some of these bacteria, and then exposed them to natural compounds. They were looking for natural molecules that might be used to fight antibiotic resistance. This effort revealed that curcumin, a molecule that is found in turmeric, as well as emodin from rhubarb, can both effectively kill bacteria in wastewater. The findings have been reported in Frontiers in Microbiology.
"Without improved treatment, wastewater could serve as a breeding ground for superbugs that may enter water resources such as rivers, lakes, and reservoirs, posing potential risks to public health," said senior study author Dr. Liyuan "Joanna' Hou of Utah State University. "Our goal was to isolate and characterize multidrug-resistant bacteria, explore the molecular mechanisms of resistance through whole-genome sequencing, and assess the potential of natural compounds as alternative mitigation strategies."
Antibiotic resistance is already a serious problem; many bacterial pathogens are now able to evade the effects of frontline antibiotics. Some are even able to resist the effects of antibiotics that are usually only used for very tough cases. One such drug of last resort is colistin.
In this work, the researchers identified some microbes in wastewater that were resistant to colistin. They also exposed microbes that were found in wastewater to another antibiotic called sulfamethoxazole to look for drug-resistant strains.
Once drug-resistant microbes were found, the investigators exposed the germs to different natural compounds including berberine, curcumin, emodin, resveratrol, rutin, and other molecules. They wanted to find compounds that could disrupt bacterial growth.
Emodin and curcumin were found to be the best at stopping bacterial cell growth and inhibiting the formation of tough colonies known as biofilms. Curcumin and higher doses of emodin were also able to interfere with cell activity. But there were Gram-negative bacteria that could resist the antibacterial effects of all of the compounds.
The scientists also sequenced the genomes of the bacteria to find the genes that encoded for resistance.
"While natural compounds like curcumin and emodin show promise in inhibiting Gram-positive multidrug-resistant bacteria, further research is needed," noted 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."
Sources: Frontiers, Frontiers in Microbiology