Amy Pruden, author of new study, associate professor, civil and environmental engineering

Virginia Tech

Q: Does this research find that our reclaimed water system (the purple pipes) might be a site where antibiotic-resistant bacteria live, multiply, and acquire antibiotic resistance?

A: "This is correct, except we cannot say for sure to what extent bacteria 'acquired' resistance in the purple pipes themselves, or if it was acquired upstream of the purple pipes.

"Our results show that there is growth of bacteria in the purple pipes, and that these bacteria carry antibiotic-resistance genes. It is not necessarily a surprise that bacteria are growing in the purple pipes, bacteria grow everywhere and most of them are harmless.

"However, this is the first study I am aware of that has actually measured the growth of bacteria in purple pipes. Also, there are natural levels and kinds of antibiotic resistance genes in nature.

"But we find that the levels of resistance genes are higher than waters unaffected by humans.

"One of the resistance genes detected at one sprinkler head, vanA, is not commonly found in soil or water and allows bacteria to survive vancomycin treatment, which is a last-resort antibiotic used to save human life."

Q: What, if any, are the potential public health concerns regarding this finding?

"There is not immediate cause for alarm because this study did not examine any specific bacteria that cause disease. It could be that all of the bacteria detected in this study, like most bacteria, are harmless to humans.

"Further studies are recommended to see if any known disease-causing bacteria are present.

"The bigger concern is not specific to the reclaimed water in Flagstaff, but is a larger global concern as more and more communities world-wide are turning to water re-use to save water.

"Water conservation is a very important and necessary goal, but to be successful, it is necessary to fully consider potential risks and reduce them to the best practical extent. Several studies around the world have shown that antibiotic resistant bacteria, including pathogens, survive and sometimes even thrive in wastewater treatment plants.

"More research is needed on reclaimed water systems to determine what risks they may pose, if any, to increasing background levels of resistance and ultimately the number of people that become ill with infections that cannot be treated with antibiotics."

Q: What about routes of exposure ... what are the concerns?

A: "The scenario is that bacteria present in the reclaimed water carry antibiotic resistance genes at higher levels than natural waters.

"Resistance genes are encoded in DNA, which can be shared between bacteria. "Reclaimed water intended for 'full body contact' could affect the natural flora of bacteria on human skin so that they are more likely to carry resistance genes and share them amongst each other.

"Then, if that individual happens to become ill and need antibiotics, the bacteria that survive the antibiotic treatment will be the ones that carry antibiotic resistance.

"With repeated antibiotic treatment (repeated illnesses), the likelihood of being infected by a disease-causing bacterium may go up.

"Bacteria are capable of carrying out each step in the above scenario. However, no research has been done to figure out the actual probability of this string of events.

Is this a one in a million scenario, or is it happening like wildfire?

"How many antibiotic resistant infections out there are the result of DNA passed along through reclaimed water?

"We don't know the answers to these questions because the research needs to be done. "This would be an important study for epidemiologists (scientists who track and quantify sources of disease) to address."

Maribeth Watwood, Professor of Microbiology, Chair

of Department of Biological Sciences, Northern Arizona University

"The presence of DNA is a far cry from the presence of pathogens," Watwood said by phone.

The genetic material could have come from dead organisms, she said.

If living bacteria were gathering antibiotic resistance in the city's reclaimed water system, "I think that would be a cause for concern," Watwood said.

Helmut Buergmann, microbiologist, The Swiss Federal Institute of Aquatic Science and Technology, Switzerland

(Buergmann was part of research team that found antibiotic resistance genes accumulating in Lake Geneva, in France and Switzerland)

"From the report ... an immediate public health risk can not be deduced.

"In this study, as well as in our own study that was cited, the focus was on tracking resistance genes or resistant bacteria in general - however these genes may occur in bacteria that themselves are harmless to human or animal health (environmental bacteria).

"Resistance (is) often found on so-called mobile genetic elements, e.g. plasmids (small circular DNA) that can be passed between different bacterial species.

"In neither of these studies pathogens (disease-inducing bacteria) were found (but also not searched for).

"What we believe however, is that these studies point toward a potential long-term problem - as we discharge microbes carrying resistance genes into the environment, it becomes more likely that these accumulate and can come into contact with, and eventually be transferred into, pathogens (disease-causing agents) - it could become 'easier' for pathogens to acquire resistances against antibiotics.

"Which is why we (and Prof. Pruden, one of the authors of the report was probably the first to suggest this) consider antibiotic resistance a new kind of contaminant.

"This is particularly true where the discharged resistant organisms come into close contact with humans.

"While the issue requires further research to fully assess the potential risks, it may be advisable to err on the side of caution and consider additional cleanup measures where this is feasible if e.g. high levels of resistance occur in waters that come into close contact with the human population."

Hans-Peter Kohler

Environmental microbiologist, The Swiss Federal Institute of Aquatic Science and Technology, Switzerland

"The report basically says that antibiotic resistance genes (ARGs) can be detected in the recycled water and that the number of such genes might increase during the residence time in the pipes.

"The question whether these findings raise a public health issue cannot be so easily answered, as there is not enough data provided on the bacteria that are the carriers of such genes (are they alive, are they pathogenic, do they really grow in the pipe system etc.) and on control systems that have been sampled with the same methods (which I deem necessary comparisons).

"I can basically agree with the next steps that the authors of the study recommend for gaining better information on potentially resistant bacteria and on the presence of antibiotics in the system."

Gerry Wright

Professor of biochemistry, biomedical sciences, specializing in antibiotic resistance, McMaster University in Ontario, Canada

"It seems quite preliminary so it's really impossible to know what the implications are. They did find some antibiotic resistance genes, but since there were no attempts to also grow bacteria, it's not clear if these are from living organisms or not.

"We've done surveys of bacteria and DNA from water samples in the past and consistently find resistance genes so this is no big surprise to me.

"They only sampled a few genes, so this is not what I would call comprehensive."

Paul Keim, Cowden Endowed Chair in microbiology at Northern Arizona University, expert on pathogens,

director of pathogen genomics program at Translational Genomics Research Institute and NAU

"This area of ARG's (antibiotic resistance genes) is an interesting one and has some value in identifying locations where antibiotics are being used. When the people of Flagstaff are treated by physicians with antibiotics, it dramatically affects their personal microflora and will increase the presence of ARGs. So, an adult human will be loaded with ARG's due to past antibiotic use.

"Once your treatment is through, the consequences of that therapy lingers on, perhaps for the rest of your life. The field of metagenomics and the microbiome are just now beginning to define the short- and long-term effects of antibiotic therapy.

"These effects are not just on pathogens (disease-causing agents), that are the intended target, but also all of our bacterial symbiont. As you know, the bacteria in our bodies outnumber the human cells 10 to 1. Humans are really a large moving vessel to support our bacteria! At least that is what the bacteria think.

"The monitoring of ARG's is not a credible method for assessing risk to human health. This is a research tool that can be used to understand the usage of antibiotics upstream, but there is no established and, really no plausible, link to human health risk.

"If there is a fear from waste water ARG's, it needs to be established that these genes are in pathogenic bacteria - that would be a real threat.

"There also needs to be an epidemiological study performed to establish the link between exposure to the water and human health. I suppose you could start with animal studies to see if they have higher level of drug resistant disease. There are lots of ways, but they need to be rigorous in their design and execution.

"There are large international studies that have identified the real threats to antibiotics as therapeutic agents. These involve the misuse of these drugs in 1) animal food production and by 2) physicians in medical practice. In both cases, humans are forcing the evolution of new pathogens with multi-drug resistance phenotypes ...

"I worry this report mis-directs our attention from the real threats. I am very worried about the development of drug resistant diseases. Waste water and environmental ARGs are not a problem relative the danger we face due to agricultural and medical practices with these very valuable drugs.

"If there is real concern about antibiotic resistant pathogens, our activities need to be directed to the real problems and not at treated wastewater. I would predict that Flagstaff residents eat large quantities of ARGS's daily in their food.

"From a relative risk standpoint, the low chance exposure to ARGs in waste water should be compared to the likely high level exposure to ARGs in our food. Not to mention the high ARGs selected for every time you take an antibiotics for illness."

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