Scientists monitoring wastewater have found a range of antibiotic-resistant bacteria; however, natural compounds from turmeric and rhubarb show promise for combating them.
When studying antibiotic-resistant bacteria in wastewater at a treatment plant, researchers discovered multidrug-resistant strains of bacteria species.
These are usually not dangerous to healthy individuals, but they could transmit genes for antibiotic resistance to more virulent bacteria, such as E. coli.
The scientists then challenged the bacteria with natural compounds which could potentially be included in wastewater treatment to kill off bacteria and fight antibiotic resistance.
The most effective were curcumin, derived from turmeric, and emodin, derived from rhubarb.
Dr Liyuan Hou of Utah State University, who led the research, explained: “Our goal was to isolate and characterise multidrug-resistant bacteria, explore the molecular mechanisms of resistance through whole-genome sequencing, and assess the potential of natural compounds as alternative mitigation strategies.”
The survival of antibiotic-resistant bacteria
Antibiotic resistance develops when bacteria evolve to be less vulnerable to antibiotics. This is more likely to happen if bacteria are exposed to a dose of vaccine which is too low to kill them all; the survivors develop resistance.
Some antibiotic-resistant bacteria are unresponsive to multiple drugs, and these infections are often treated with ‘last resort’ drugs like colistin. However, when Hou and her colleagues tested samples of effluent from a wastewater treatment plant in Logan, Utah, they found some colonies of bacteria that were resistant even to colistin.
This underlines the urgency of finding ways to prevent and treat bacterial infections that minimise the use of antibiotics.
Fighting back against resistance
The scientists screened their samples using one antibiotic, sulfamethoxazole, to identify nine different strains of antibiotic-resistant bacteria.
These strains of bacteria were then tested against multiple classes of antibiotics to determine how many of them were resistant. Their genomes were also sequenced, which allowed the scientists to identify not just the bacteria themselves but also the genes that contribute to their antibiotic resistance.
“While not traditionally classified as top-priority clinical pathogens, some are opportunistic pathogens associated with infections such as pneumonia in immunocompromised individuals,” explained Hou.
“These bacteria could also act as environmental reservoirs, transferring resistance genes to other bacteria, including clinically relevant pathogens.”
The role of natural compounds in providing antimicrobial properties
The scientists challenged colonies of these bacteria with different concentrations of 11 natural compounds: berberine, chlorflavonin, chrysin, curcumin, emodin, hesperidin, naringin, quercetin, resveratrol, rutin, and 2’-hydroxyflavone.
They then examined various measurements of the colonies’ health, including cell growth, biofilm formation, and the level of bacterial activity.
They found that emodin and curcumin were most effective in inhibiting cell growth and biofilm formation, while curcumin and a higher dose of emodin reduced cell activity; however, a low dose of emodin increased activity in several strains.
However, Gram-negative bacteria, such as Chryseobacterium, were resistant to all the compounds.
Hou concluded: “While natural compounds like curcumin and emodin show promise in inhibiting Gram-positive multidrug-resistant bacteria, further research is needed.
“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.”
