New Study Finds Antibiotic-Resistant Bacteria Genes in Flagstaff’s Reclaimed Water

sprinkler by Todd MorrisA study headed by a Virginia Tech researcher suggests that the City of Flagstaff’s reclaimed water system may be a breeding ground for antibiotic-resistant bacteria; however, opinions diverge as to whether the bacteria could ultimately harm residents.

Some researchers say the study’s findings suggest that otherwise normal bacteria living in the system are developing resistance to antibiotics while in the system, according to the Arizona Daily Sun; other researchers doubt the problem is significant.

The researchers claim this is “the only quantitative survey of antibiotic resistance genes in recycled water.” Other scientists note that the researchers simply looked for the presence of these genes in the water rather than examined whether potentially harmful bacteria were present.

Flagstaff’s wastewater is treated in multiple stages, which includes UV treatment and the addition of bleach before it is distributed to irrigate local golf courses, the grounds of city schools such as Northern Arizona University, and municipal parks, according to the Arizona Daily Sun.

The report explains that:

Antibiotic resistance is a growing problem and is a major challenge to human medicine because it results in drugs losing their effectiveness for treating bacterial infections. Bacteria are able to fight antibiotics through many mechanisms, all of which are encoded in their DNA by antibiotic resistance genes (ARGs). ARGs have been found in wastewater treatment systems, which receive antibiotics and resistant gastrointestinal flora excreted by humans. […] This has raised the question about the persistence of ARGs in recycled water.

sprinklers by sarcozonaThe researchers specifically looked for the presence of five types of antibiotics at irrigation sites — which included soccer fields, baseball fields, and parks — in Flagstaff: tetracyclines, sulfonamides, macrolides, glycopeptides, and methicillin.

Amy Pruden, the author of the study and an associate professor of civil and environmental engineering at Virginia Tech, told the Arizona Daily Sun that the bacteria might be living and breeding in the city’s reclaimed water system, “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. […] It is not necessarily a surprise that bacteria are growing […] bacteria grow everywhere and most of them are harmless.” She adds that some types of antibiotic resistance genes occur naturally.

She adds that, “One of the resistance genes detected at one sprinkler head […] 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.”

The City of Flagstaff was compelled to study the matter after Robin Silver, a local physician, and other residents presented their concerns to Flagstaff’s leaders. The city has clearly stated that neither the state nor the United States Environmental Protection Agency regulate antibiotic-resistant genes in water.

Hans-Peter Kohler, an environmental microbiologist with the Swiss Federal Institute of Aquatic Science and Technology, Switzerland, told the newspaper:

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 — and on control systems that have been sampled with the same methods, which I deem necessary comparisons.

“It seems quite preliminary so it’s really impossible to know what the implications are,” stated Gerry Wright, a professor of biochemistry at McMaster University in Ontario, Canada, who specializes in antibiotic resistance. “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.”

The City of Flagstaff noted:

We understand that studying antibiotic-resistant genes in reclaimed water both at the local and national levels is very early on in its research development. We also understand from this study that no quantitative health risk conclusions can be drawn from this limited information.

Pruden states there is no cause for alarm as most bacteria are actually harmless to humans. She adds:

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.

The next course of action, according to the Arizona Daily Sun, is for the city to appoint an advisory panel. Its members would be tasked with developing a plan for studying particulates detected in untreated water, drinking water, and reclaimed water; and how to proceed based on those results. According to the newspaper, the city has “no immediate plans to alter the ways in which reclaimed wastewater is distributed and applied throughout the city.”

Images by Todd Morris (top) and sarcozona.

6 Responses to “New Study Finds Antibiotic-Resistant Bacteria Genes in Flagstaff’s Reclaimed Water”

  1. Dr Edo McGowan 

    We are running a parallel study in Santa Barbara on recycled water. Unlike the Flagstaff study, we did run tests for antibiotic resistant bacteria and using disk diffusion tests did find resistant bacteria and these were resistant to 11 of the 12 challenge antibiotics. We also ran tests on recycled water from an adjacent sewer district and again found bacteria that were multi drug resistant. Since the same or similar technology is used across the nation, I would suspect that these results could be easily duplicated. We also ran tests on the potable side and got similar results out of filtering systems and equipment that makes presumably sterile water.

    Dr Edo McGowan, Medical Geo-hydrology

  2. ldpaulson 

    Thank you for your comment.

    Are your results scheduled to be published? It would be interesting to see how your study (and others) compares and contrasts the Flagstaff findings.

    As a result, do you think the US EPA, NIH, or other government agencies will support a long-term, comprehensive study of antibiotic resistant bacteria in municipal water supplies?

    — ldp

  3. Dr Edo McGowan 

    To Idpaulson:

    Sorry, did not pick up on this until just now. Problem with US/EPA will be with their long-term promoting the land application of sewage sludge (biosolids). For example, see the study of Sugar Creek ( where the drainage from sludged fields was associated with the movement of resistance to recreational water bodies. Also, the WERF work by Higgins and Murthy on resuscitation of viable but non-culturable (VBNC) bacteria saw the numbers in sewage sludge shoot up several magnitudes in just a few minutes. When added to the WERF report by Rose (WERF 00-PUM-2T) and the paper by Harwood, on reclaimed water, these should have raised red flags. The abstract to the Harwood study on reclaimed water notes—” Multiple samplings conducted at each facility over a 1-year period. Larger sample volumes for indicators (0.2 to 0.4 liters) and pathogens (30 to 100 liters) resulted in more sensitive detection limits than are typical of routine monitoring. Microorganisms were detected in disinfected effluent samples at the following frequencies: total coliforms, 63%; fecal coliforms, 27%; enterococci, 27%; C. perfringens, 61%; F-specific coliphages, ∼40%; and enteric viruses, 31%. Cryptosporidium oocysts and Giardia cysts were detected in 70% and 80%, respectively, of reclaimed water samples. ” In the late 1970s, the US/EPA did a major study that documented that sewer plants were a principal factor in putting resistant bacteria into the aquatic environment of the nation. That paper cited other works stretching back to the 1960s that said the same thing—-sewer plants make antibiotic resistance. The EPA study for some reason, including all data associated with it was removed from the EPA data base. There was nothing wrong with the study, but I suspect it would raise questions about antibiotic resistant pathogens being in sewage sludge. The question would draw attention to the promotion of land applied sewage sludge and the potential for sewage sludge to spread resistance across the nation’s farmland. That would interfere with the promotion of sewage sludge by both US/EPA and USDA. The issue with reclaimed water is not dissimilar because we are discussing resistance. Once in the human gut, the genes can be kept for quite long periods (years) and thus act as a lending library to incoming pathogens. Maria Sjolund (2005) indicated that resistance in the normal flora, which may last years, might contribute to increased resistance in higher-grade pathogens through inter-species transfer. Sjolund et al go on to note that since populations of the normal biota are large, this affords the chance for multiple and different resistant variants to develop. This thus enhances the risk for spread to populations of pathogens. Furthermore, there is crossed resistance. Thus, with resistant organisms and the capacity of the gut biota to take in genes and multiply bacteria, the old paradigm of infective dose may no longer be applicable here. How should this be addressed?

    As to our data, we are testing both the reclaimed water (Recycled in California’s nomenclature) as it first leaves the plant with two sets of tests and again as it exits the delivery system via sprinklers or hose bibs. The first set of tests is the MPN, that test is used essentially by all sewer plants and the one both Rose in the WERF study and Harwood in the peer reviewed article have discuss as “The failure of measurements of single indicator organism to correlate with pathogens suggests that public health is not adequately protected by simple monitoring schemes based on detection of a single indicator, particularly at the detection limits routinely employed.” The second set of tests we used is the disk diffusion on Muller-Hinton. What we are finding is that at the plant, with MPN, we get very low readings or non-detect, but at the end of the pipe (point of use) the numbers are off the chart. This, we think, is either resuscitation of VBNC or sloughing biofilms or both. On one of our recent test runs we were getting resistant genes even-though the plant was sending water from the potable supply through the system that formerly contained reclaimed water. This tends to show the sloughing of biofilms.The results for the disk diffusion at both points gives us multi-drug resistant bacteria that of course would not be seen on the MPN. Thus the MPN could be throwing false negatives, especially when considering results from the disk diffusion. We have also done studies on antibiotic resistant genes (ARGs) and we are finding them in the delivered water (POU). Yes, these data will, at some point, be published. Part of our problem is getting the regulatory community interested in this. Perhaps those in Arizona have a more responsive set in their regulatory community.

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