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Chicken coops, wastewater plants serve as breeding grounds for antibiotic resistance
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Researchers investigating the dissemination of antibiotic resistance genes in developing countries found that resistance gene transfer was more likely to occur in areas such as chicken coops and modern wastewater treatment facilities, according to recent findings.
“It’s relatively easy for disease-causing bacteria that are treatable with antibiotics to become resistant to those antibiotics quickly,” Gautam Dantas, PhD, associate professor of pathology and immunology at Washington University School of Medicine, said in a press release. “If these bacteria happen to come into contact with other microbes that carry resistance genes, those genes can pop over in one step. We estimate that such gene-transfer events are generally rare, but they are more likely to occur in these hot spots we identified.”
Gautam Dantas
Dantas and colleagues evaluated the incidence of resistance gene transfer in a rural village of subsistence farmers in El Salvador, as well as the outskirts of Lima, Peru. Both areas are low-income communities representing a majority of the global population. Their microbial ecosystems, however, are significantly understudied, the researchers wrote.
“Not only do the communities in our study serve as models for how most people live, they also represent areas of highest antibiotic use,” Dantas said in the release. “Access to these drugs is over-the-counter in many low-income countries. Since no prescription is required, we expect antibiotic use in these areas to be high, putting similarly high pressure on bacteria to develop resistance to these drugs.”
During the 2-year study period, the researchers examined 263 fecal samples from 115 participants and 209 environmental samples collected from 27 households and surrounding areas. The environmental samples included animal feces, soil, water, and specimens collected from a districtwide sewage system with a modern wastewater treatment plant in Peru.
Figure 1. Researchers identified "hot spots" for resistance gene transfer in a rural village of subsistence farmers in El Salvador, as well as the outskirts of Lima, Peru.
Source: Pablo Tsukayama
According to the researchers, bacteria that were closely related and those from like environments had similar resistance genes. For example, resistance genes in human feces were similar to those in animal feces, and resistance genes in soil were similar to those in water.
“We were not terribly surprised by the resistance genes that track with bacterial family trees,” Dantas said. “On the other hand, the genes we found that break the hereditary trend are quite worrisome. Genes that are the exceptions to the rule — that are not similar to the surrounding DNA — are the ones that are most likely to have undergone a gene-transfer event. And they are the resistance genes at highest risk of future transmission into unrelated bacteria.”
A comparison of human feces with soil samples revealed fecal bacteria were most similar to bacteria in soil collected near chicken coops in El Salvador. The bacteria shared 80 antibiotic resistance proteins, including those commonly found in Enterobacteriaceae.
“Soils in the chicken coops we studied appear to be hot spots for the exchange of resistance genes,” Dantas said. “This means disease-causing bacteria in chickens are at risk of sickening humans and transferring their resistance genes in the process. Our study demonstrates the importance of public health guidelines that advise keeping animals out of cooking spaces.”
Dantas and colleagues also compared influent and effluent substances from the local wastewater treatment plant in Peru. While sewage treatment successfully reduced human fecal bacteria, antibiotic resistance genes were able to survive. This may allow for the reintroduction of antibiotic resistance into areas where wastewater effluent is discharged, which in the current analysis, was the Pacific Ocean and public parks.
The researchers then measured antibiotics in sewage systems, which may impact resistome diversity, they wrote. Chloramphenicol, ciprofloxacin, tetracycline, trimethoprim and sulfamethoxazole were regularly detected in pre-treated samples. Meanwhile, sulfamethoxazole was the only antibiotic found in effluent samples.
“All the antibiotics we detected in the pre-treated water were among the top 20 sold in Peru,” Dantas said in the release. “These findings have implications for public health, perhaps in designing future wastewater treatment plants and in making policy decisions about whether antibiotics should be available without a prescription.” – by Stephanie Viguers
Disclosure: Dantas reports no relevant financial disclosures.
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