Tag: Environment

A novel antibiotic? Pretty cool, but…

In a recent paper in Nature, a completely new antibiotic – teixobactin – is described (1). The really cool thing about this antibiotic is that it was discovered in a screen of uncultured bacteria, grown using new technology that enable controlled growth of single colonies in situ. I really like this idea, and I think the prospect of a novel antibiotic using a previously unexploited mechanism is super-promising, particularly in the light of alarming resistance development in clinically important pathogens (2,3). What really annoys me about the paper is the claim (already in the abstract) that since “we did not obtain any mutants of Staphylococcus aureus or Mycobacterium tuberculosis resistant to teixobactin (…) the properties of this compound suggest a path towards developing antibiotics that are likely to avoid development of resistance.” To me, this sounds pretty much like a bogus statement; in essence telling me that we apparently have not learned anything from the 70 years of antibiotics usage and resistance development. After working with antibiotic resistance a couple of years, particularly from the environmental perspective, I have a very disturbing feeling that there is already resistance mechanisms against teixobactin waiting out in the wild (4,5). Pretending that lack of mutation-associated resistance development means that there could not be resistance development did not help vancomycin (6,7), and we now see VRE (Vancomycin Resistant Enterococcus) showing up as a major problem in clinics. The “avoid development of resistance” claim is downright irresponsible, and the cynic in me cannot help to think that NovoBiotic Pharmaceuticals (the affiliation of almost half of the authors) has a monetary finger in this jar. In the end, time will tell how “resistance-resilient” teixobactin is and how well we can handle the gift of a novel antibiotic.

  1. Ling LL, Schneider T, Peoples AJ, Spoering AL, Engels I, Conlon BP, Mueller A, Schäberle TF, Hughes DE, Epstein S, Jones M, Lazarides L, Steadman VA, Cohen DR, Felix CR, Fetterman KA, Millett WP, Nitti AG, Zullo AM, Chen C, Lewis K: A new antibiotic kills pathogens without detectable resistance. Nature (2015). doi:10.1038/nature14098
  2. Finley RL, Collignon P, Larsson DGJ, McEwen SA, Li X-Z, Gaze WH, Reid-Smith R, Timinouni M, Graham DW, Topp E: The scourge of antibiotic resistance: the important role of the environment. Clin Infect Dis, 57: 704–710 (2013).
  3. French GL: The continuing crisis in antibiotic resistance. Int J Antimicrob Agents, 36 Suppl 3:S3–7 (2010).
  4. Bengtsson-Palme J, Boulund F, Fick J, Kristiansson E, Larsson DGJ: Shotgun metagenomics reveals a wide array of antibiotic resistance genes and mobile elements in a polluted lake in India. Frontiers in Microbiology, 5: 648 (2014).
  5. Larsson DGJ: Antibiotics in the environment. Ups J Med Sci, 119: 108–112 (2014).
  6. Wright GD: Mechanisms of resistance to antibiotics. Curr Opin Chem Biol, 7:563–569 (2003).
  7. Werner G, Strommenger B, Witte W: Acquired vancomycin resistance in clinically relevant pathogens. Future Microbiol, 3: 547–562 (2008).

Polluted lake paper in final form

Our paper describing the bacterial community of a polluted lake in India has now been typeset and appears in its final form in Frontiers in Microbiology. If I may say so, I think that the paper turned out to be very goodlooking and it is indeed nice to finally see it in print. The paper describes an unprecedented diversity and abundance of antibiotic resistance genes and genes enabling transfer of DNA between bacteria. We also describe a range of potential novel plasmids from the lake. Finally, the paper briefly describes a new approach to targeted assembly of metagenomic data — TriMetAss — which can be downloaded here.

Reference:
Bengtsson-Palme J, Boulund F, Fick J, Kristiansson E, Larsson DGJ: Shotgun metagenomics reveals a wide array of antibiotic resistance genes and mobile elements in a polluted lake in India. Frontiers in Microbiology, 5, 648 (2014). doi: 10.3389/fmicb.2014.00648

Published paper: Antibiotic resistance genes in a polluted lake

The first work in which I have employed metagenomics to investigate antibiotic resistance has been accepted in Frontiers in Microbiology, and is (at the time of writing) available as a provisional PDF. In the paper (1), which is co-authored by Fredrik Boulund, Jerker Fick, Erik Kristiansson and Joakim Larsson, we have used shotgun metagenomic sequencing of an Indian lake polluted by dumping of waste from pharmaceutical production. We used this data to describe the diversity of antibiotic resistance genes and the genetic context of those, to try to predict their genetic transferability. We found resistance genes against essentially every major class of antibiotics, as well as large abundances of genes responsible for mobilization of genetic material. Resistance genes were estimated to be 7000 times more abundant in the polluted lake than in a Swedish lake included for comparison, where only eight resistance genes were found. The abundances of resistance genes have previously only been matched by river sediment subject to pollution from pharmaceutical production (2). In addition, we describe twenty-six known and twenty-one putative novel plasmids from the Indian lake metagenome, indicating that there is a large potential for horizontal gene transfer through conjugation. Based on the wide range and high abundance of known resistance factors detected, we believe that it is plausible that novel resistance genes are also present in the lake. We conclude that environments polluted with waste from antibiotic manufacturing could be important reservoirs for mobile antibiotic resistance genes. This work further highlights previous findings that pharmaceutical production settings could provide sufficient selection pressure from antibiotics (3) to drive the development of multi-resistant bacteria (4,5), resistance which may ultimately end up in pathogenic species (6,7). The paper can be read in its entirety here.

References:

  1. Bengtsson-Palme J, Boulund F, Fick J, Kristiansson E, Larsson DGJ: Shotgun metagenomics reveals a wide array of antibiotic resistance genes and mobile elements in a polluted lake in India. Frontiers in Microbiology, Volume 5, Issue 648 (2014). doi: 10.3389/fmicb.2014.00648
  2. Kristiansson E, Fick J, Janzon A, Grabic R, Rutgersson C, Weijdegård B, Söderström H, Larsson DGJ: Pyrosequencing of antibiotic-contaminated river sediments reveals high levels of resistance and gene transfer elements. PLoS ONE, Volume 6, e17038 (2011). doi:10.1371/journal.pone.0017038.
  3. Larsson DGJ, de Pedro C, Paxeus N: Effluent from drug manufactures contains extremely high levels of pharmaceuticals. J Hazard Mater, Volume 148, 751–755 (2007). doi:10.1016/j.jhazmat.2007.07.008
  4. Marathe NP, Regina VR, Walujkar SA, Charan SS, Moore ERB, Larsson DGJ, Shouche YS: A Treatment Plant Receiving Waste Water from Multiple Bulk Drug Manufacturers Is a Reservoir for Highly Multi-Drug Resistant Integron-Bearing Bacteria. PLoS ONE, Volume 8, e77310 (2013). doi:10.1371/journal.pone.0077310
  5. Johnning A, Moore ERB, Svensson-Stadler L, Shouche YS, Larsson DGJ, Kristiansson E: Acquired genetic mechanisms of a multiresistant bacterium isolated from a treatment plant receiving wastewater from antibiotic production. Appl Environ Microbiol, Volume 79, 7256–7263 (2013). doi:10.1128/AEM.02141-13
  6. Pruden A, Larsson DGJ, Amézquita A, Collignon P, Brandt KK, Graham DW, Lazorchak JM, Suzuki S, Silley P, Snape JR., et al.: Management options for reducing the release of antibiotics and antibiotic resistance genes to the environment. Environ Health Perspect, Volume 121, 878–885 (2013). doi:10.1289/ehp.1206446
  7. Finley RL, Collignon P, Larsson DGJ, McEwen SA, Li X-Z, Gaze WH, Reid-Smith R, Timinouni M, Graham DW, Topp E: The scourge of antibiotic resistance: the important role of the environment. Clin Infect Dis, Volume 57, 704–710 (2013). doi:10.1093/cid/cit355

Published paper: Detoxification genes in marine bacteria

I just got word from BMC Genomics that my most recent paper has just been published (in provisional form; we still have not seen the edited proofs). In this paper (1), which I have co-authored with Anders Blomberg, Magnus Alm Rosenblad and Mikael Molin, we utilize metagenomic data from the GOS-expedition (2) together with fully sequenced bacterial genomes to show that:

  1. Detoxification genes in general are underrepresented in marine planktonic bacteria
  2. Surprisingly, the detoxification that show a differential distribution are more abundant in open ocean water than closer to the coast
  3. Peroxidases and peroxiredoxins seem to be the main line of defense against oxidative stress for bacteria in the marine milieu, rather than e.g. catalases
  4. The abundance of detoxification genes does not seem to increase with estimated pollution.

From this we conclude that other selective pressures than pollution likely play the largest role in shaping marine planktonic bacterial communities, such as for example nutrient limitations. This suggests substantial streamlining of gene copy number and genome sizes, in line with observations made in previous studies (3). Along the same lines, our findings indicate that the majority of marine bacteria would have a low capacity to adapt to increased pollution, which is relevant as large amounts of human pollutants and waste end up in the oceans every year. The study exemplifies the use of metagenomics data in ecotoxicology, and how we can examine anthropogenic consequences on life in the sea using approaches derived from genomics. You can read the paper in its entirety here.

References:

  1. Bengtsson-Palme J, Alm Rosenblad M, Molin M, Blomberg A: Metagenomics reveals that detoxification systems are underrepresented in marine bacterial communities. BMC Genomics. Volume 15, Issue 749 (2014). doi: 10.1186/1471-2164-15-749 [Paper link]

  2. Yooseph S, Sutton G, Rusch DB, Halpern AL, Williamson SJ, Remington K, Eisen JA, Heidelberg KB, Manning G, Li W, Jaroszewski L, Cieplak P, Miller CS, Li H, Mashiyama ST, Joachimiak MP, Van Belle C, Chandonia J-M, Soergel DA, Zhai Y, Natarajan K, Lee S, Raphael BJ, Bafna V, Friedman R, Brenner SE, Godzik A, Eisenberg D, Dixon JE, Taylor SS, et al: The Sorcerer II Global Ocean Sampling expedition: expanding the universe of protein families. PLoS Biology. 5:e16 (2007).
  3. Yooseph S, Nealson KH, Rusch DB, McCrow JP, Dupont CL, Kim M, Johnson J, Montgomery R, Ferriera S, Beeson KY, Williamson SJ, Tovchigrechko A, Allen AE, Zeigler LA, Sutton G, Eisenstadt E, Rogers Y-H, Friedman R, Frazier M, Venter JC: Genomic and functional adaptation in surface ocean planktonic prokaryotes. Nature. 468:60–66 (2010).

EU report on effect-based tools for ecotoxicology

Because of my previous involvement in a Swedish report on toxicological monitoring using (meta)-genomics tools [1], I also became in a related EU report on effect-based tools for use in toxicology in the aquatic environment. This report has recently been officially published [2], and can be found here, with the annex available on the European Commission document website. My contribution to this report has been in the genomics and metagenomics section (Chapter 7: OMICS techniques), in which I wrote the metagenomics part and contributed to the rest. I personally think this is a quite forward-thinking report, which is nice for a large institution such as the EU.

  1. Länsstyrelsen i Västra Götalands län. (2012). Swedish monitoring of hazardous substances in the aquatic environment (No. 2012:23). (A.-S. Wernersson, Ed.) Current vs required monitoring and potential developments (pp. 1–291). Länsstyrelsen i Västra Götalands län, vattenvårdsenheten.
  2. Wernersson A-S, Carere M, Maggi C, Tusil P, Soldan P, James A, Sanchez W, Broeg K, Kammann U, Reifferscheid G, Buchinger S, Maas H, Van Der Grinten E, Ausili A, Manfra L, Marziali L, Polesello S, Lacchetti I, Mancini L, Lilja K, Linderoth M, Lundeberg T, Fjällborg B, Porsbring T, Larsson DGJ, Bengtsson-Palme J, Förlin L, Kase R, Kienle C, Kunz P, Vermeirssen E, Werner I, Robinson CD, Lyons B, Katsiadaki I, Whalley C, den Haan K, Messiaen M, Clayton H, Lettieri T, Negrão Carvalho R, Gawlik BM, Dulio V, Hollert H, Di Paolo C, Brack W (2014). Technical Report on Aquatic Effect-Based Monitoring Tools. European Commission. Technical Report 2014-077, Office for Official Publications of European Communities, ISBN: 978-92-79-35787-9. doi:10.2779/7260

Swedish monitoring of hazardous substances

I was recently involved as an adviser in a report by the County Administrative Board in Västra Götaland (Länsstyrelsen) which has now been published [1]. [UPDATE: The PDF link at Länsstyrelsen’s page does not seem to work, but leads to another report in Swedish. I have reported this error to the web admin, we’ll see what happens. Once again, the PDF seems to work.] The report aims to identify gaps in the current monitoring system of hazardous substances in the Swedish environment. The report deals with effect based monitoring tools and their usefulness for predicting and/or observing effects of hazardous substances in the environment. The overall conclusion of the report is that there are several gaps in both knowledge and techniques, and a need for developing new resources. However, Sweden still has a good potential to adapt the monitoring system to fill the needs. I have been involved in one of the last chapters, describing the use of metagenomics if study ecosystem function (chapter 30.3). For people with an interest in environmental monitoring, the report is an interesting read in its entirety. For those more interested in applications for metagenomics I recommend turning to page 285 and continue to the end of the report (it’s only five pages on metagenomics, so you’ll manage).

  1. Länsstyrelsen i Västra Götalands län. (2012). Swedish monitoring of hazardous substances in the aquatic environment (No. 2012:23). (A.-S. Wernersson, Ed.) Current vs required monitoring and potential developments (pp. 1–291). Länsstyrelsen i Västra Götalands län, vattenvårdsenheten.

Blurring the line between cause and effect

Finally I have gotten around to finish my reply to Amy Pruden, who gave me some highly relevant and well-balanced critique of my previous post on antibiotic resistance genes as pollutants, back in early March. Too much came in between, but now I am more or less content with my answer.

First of all I would like to thank Amy for her response to my post on antibiotic resistance genes as pollutants. Her reply is very well thought-through, and her criticism of some of my claims is highly appropriate. For example, I have to agree on that the extracellular DNA pool is vastly uncharacterized, and that my statement on this likely not being a source of resistance transmission is a bit of a stretch. The role of “free-floating” DNA in gene transfer must be further elucidated, and currently we do not really know whether it is important or not; and if so, to what extent it contributes.

However, I still maintain my view that there are problems with considering resistance genes pollutants, mainly because the blurs the line between cause and effect. If we for example consider photosynthetic microbial communities exposed to the photosynthesis inhibitor Irgarol, the communities develop (or acquires) tolerance towards the compound over time (Blanck et al 2009). The tolerance mechanism has been attributed to changes in the psbA gene sequence (Eriksson et al. 2009). If we address this issue from a “resistance-genes-as-pollutants” perspective, would these tolerance-conveying psbA genes be considered pollutants? It would make sense to do so as they are unwanted in weed control circumstances; much like antibiotic resistance genes are unwanted in clinical contexts. It could be argued here that in these microbes such tolerance-associated psbA genes do not cause any harm. But consider for a moment that they did not occur microbes, but in weeds, would they then be considered pollutants? In weeds they would certainly cause (at least economic) harm. Furthermore, say that the tolerance-conveying psbA genes have the ability to spread (which is possible at least in marine settings assisted by phages (Lindell et al 2005)), would that make these tolerance genes pollutants? It is quite of a stretch but as plants can take up genetic material from bacteria (c.f. Clough & Bent 1998, although this is not my area of expertise), there could be a spreading potential to weeds of these tolerance-conveying psbA genes.

What I am trying to say is that if we start viewing antibiotic resistance genes as pollutants per se, instead of looking at the chemicals (likely) causing resistance development, we start blurring the line between cause and effect. Resistance genes in the environment provide resilience to communities (at least to some species – the issue of ecosystem function responses to toxicants is a highly interesting area one as well). However, in this case the resilience itself is the problem, because we think it can spread into human and animal pathogens. But from my point of view, the causes are still use, overuse, misuse and inappropriate release of antibiotics. Therefore, I maintain that we should be careful with pointing out resistance genes by themselves as pollutants – if we do not have very good reasons to do so.

Nevertheless, that does not mean that I think Pruden, and many other prominent authors, are wrong when they refer to resistance genes as pollutants. All I want to point out is that the statement in itself is a bit dangerous, as it might draw attention towards mitigating the effect of pollution, instead of mitigating the source of pollution itself. The persistence of resistance genes in bacterial genomes is alarming (Andersson & Hughes 2011), as it means that removal of selection pressures may have less effect on resistance gene abundance than anticipated. However, the only way I see out of this darkening scenario is to:

  1. Minimize the selection pressure for resistance genes in the clinical setting
  2. Immediately reduce environmental release of antibiotics, both from manufacturing and use. This primarily has to be done using better treatment technologies
  3. Find the routes that enable environmental bacteria to disseminate resistance genes to clinically relevant species and strains – and close them
  4. Develop antibiotics exploiting new mechanisms to eliminate bacteria

Lastly, I would like to thank Amy for taking my critique seriously – I think we agree on a lot more than we differ on, and I look forward to have this discussion in person at some point. I think we both agree that regardless of our standpoint, the terminology used in this context deserves to be discussed. Nevertheless, the terminology is quite unimportant compared to the values that are at stake – our fundamental ability to treat diseases and perform modern health care.

References

  1. Andersson, D.I. & Hughes, D., 2011. Persistence of antibiotic resistance in bacterial populations. FEMS Microbiology Reviews, 35(5), pp.901–911.
  2. Blanck, H., Eriksson, K. M., Grönvall, F., Dahl, B., Guijarro, K. M., Birgersson, G., & Kylin, H. (2009). A retrospective analysis of contamination and periphyton PICT patterns for the antifoulant irgarol 1051, around a small marina on the Swedish west coast. Marine pollution bulletin, 58(2), 230–237. doi:10.1016/j.marpolbul.2008.09.021
  3. Clough, S. J., & Bent, A. F. (1998). Floral dip: a simplified method for Agrobacterium-mediated transformation of Arabidopsis thaliana. The Plant journal : for cell and molecular biology, 16(6), 735–743.
  4. Eriksson, K. M., Clarke, A. K., Franzen, L.-G., Kuylenstierna, M., Martinez, K., & Blanck, H. (2009). Community-level analysis of psbA gene sequences and irgarol tolerance in marine periphyton. Applied and Environmental Microbiology, 75(4), 897–906. doi:10.1128/AEM.01830-08
  5. Lindell, D., Jaffe, J. D., Johnson, Z. I., Church, G. M., & Chisholm, S. W. (2005). Photosynthesis genes in marine viruses yield proteins during host infection. Nature, 438(7064), 86–89. doi:10.1038/nature04111

More on antibiotic resistance genes as pollutants

I received some well-formulated and very much relevant critique on my post Why viewing antibiotic resistance genes as a pollutant is a problem, which I wrote in January. To encourage the debate on this issue, I have asked the author – Amy Pruden – for her permission to republish it here, to give it the visibility it deserves. I intend to follow up on her comments in a forthcoming post, but I have not had time to formulate my answer yet. Until then, please read and contemplate both the original post by me, and Amy’s highly relevant answer below. I hope that we can continue this discussion in the same fruitful manner!

First of all I thank Johan Bengtsson for initiating a lively and much needed discussion on which pollutant we should precisely be targeting, antibiotics or antibiotic resistance genes (ARGs), in our important war against the spread of antibiotic resistance. As Bengtsson correctly alludes, my perspective comes from that of environmental science and engineering. At the core of these disciplines is defining and predicting the fate of pollutants in the environment, as well as designing appropriate means for their control. For these purposes, the definition of the pollutant of interest is of central importance. In general they may be defined as “undesired or harmful constituents within an environmental matrix, usually of human origin.” Pollutants may be classified in all shapes and sizes, including conservative (i.e., not subject to degradation or growth), non-conservative, biotic, abiotic, dissolved, and suspended (i.e., not dissolved). Thus, the first point, regarding the nature by which ARGs are spread disqualifying them from being considered as pollutants, is inaccurate.

At the same time, I recognize and agree that ARGs are indeed a natural and important aspect of the natural ecosystem. I commend recent work revealing the vast “antibiotic-resistome” in ancient environments (D’Costa et al. 2011; Allen et al. 2009), as it provides an essential understanding of the baseline antibiotic resistance in the pre-antibiotic era, which may serve as contrast for observations in the current antibiotic era. Thus, I agree that not all ARGs are pollutants, rather, anthropogenic sources of ARGs are the agents of interest. Perhaps I and others are guilty of not making this distinction more clear. It should also be pointed out that likewise, the vast majority of antibiotics in use today are derived from natural compounds, yet I agree that they can also serve as important environmental pollutants of concern. Thus, it is not necessarily whether the constituent is naturally occurring that defines the pollutant, rather its magnitude and distribution, as influenced by human activities.

It is agreed that viewing ARGs as contaminants does pose technical challenges. They may amplify within a host, or attenuate due to degradation or diminished selection pressure. However, with appropriate understanding of the mechanisms of transport and persistence, accurate models may be developed. I do contend that the jury is still out regarding the relative importance of extracellular and intracellular ARGs. The pool of extracellular DNA remains vastly uncharacterized, and some studies suggest that it is more extensive than previously thought (Wu et al. 2009; Corinaldesi et al. 2005). Other studies have specifically demonstrated the capability of extracellular ARGs to persist under certain environmental conditions and maintain its integrity for host uptake (Cai et al. 2007). While focusing attention on individual resistant strains of bacteria has merit in some instances, this approach is also greatly limited by the unculturability of the vast majority of environmental microbes. As we have now entered the metagenomic era, we now have the tools to tackle the complexity of resistance elements in the environment and precisely define the human influence. Distribution of ARGs may also be considered in parallel with key genetic elements driving their horizontal gene transfer, such as plasmids, transposons, and integrons.

Regarding the antibiotics themselves, clearly they are important. The direct relationship between clinical use and increasing rates of antibiotic resistance is well-documented and certainly continued vigilance in promoting their appropriate use and disposal is called for. What remains much foggier is the exact role of environmental antibiotics in enabling selection once released into the environment. There is good evidence that even sub-inhibitory levels of antibiotics can stimulate various functions in the cell, especially horizontal gene transfer, as reviewed recently by Aminov (2011). However, environmentally-relevant concentrations driving selection of resistant strains are largely unknown. Further, at what point along a discharge pathway from wastewater treatment plant or livestock lagoon do ARGs persist independently of ambient antibiotic conditions? Indeed, some studies have noted correlations between antibiotics and ARGs in environmental matrices while others have noted an absence of such a correlation. In either case, it appears that ARGs persist and are transported further along pathways than antibiotics, suggesting distinct factors governing transport (McKinney et al. 2010; Peak et al. 2007). Research is needed to better understand the mechanisms at play, such as antibiotics other selectors (e.g. metals and other toxins), in leaving a human foot-print on environmental reservoirs of resistance. Nonetheless, a reasonable approach for mitigating risk seems to be focusing attention on developing appropriate technologies for eliminating both antibiotics and genetic material from wastestreams.

Thanks again for opening this discussion- I hope to meet you at a conference sometime in the future!

References
1. Allen, H.K., Moe, L.A., Rodbumrer, J., Gaarder, A., & Handelsman, J., 2009. Functional metagenomics reveals diverse b-lactamases in a remote Alaskan soil. ISME 3, pp. 243-251.
2. Aminov, R.I., 2011. Horizontal gene exchange in environmental microbiota. Front. Microbiol. 2,158 doi:10.3389/fmicb.2011.00158.
3. Corinaldesi, C., Danovaro, R. & Dell‘Anno, A., 2005. Simultaneous recovery of intracellular and extracellular DNA suitable for molecular studies from marine sediments. Appl. Environ. Microbiol. 71, pp. 46-50.
4. D’Costa, V.M., McGrann, K.M., Hughes, D.W., & Wright, G.D., 2006. Sampling the antibiotic resistome. Science 311, pp. 374-377.
5. McKinney, C.W., Loftin, K.A., Meyer, M.T., Davis, J.G., & Pruden, A., 2010. tet and sul antibiotic resistance genes in livestock lagoons of various operation type, configuration, and antibiotic occurrence. Environ. Sci. Technol. 44 (16), pp. 6102-6109.
6. Peak, N., C.W. Knapp; R.K. Yang; M.M. Hanfelt; M.S. Smith, D.S. Aga, & Graham, D. W., 2007. Abundance of six tetracycline resistance genes in wastewater lagoons at cattle feedlots with different antibiotic use strategies. Environ. Microbiol. 9 (1), pp. 143–151.
7. Wu, J. F. & Xi, C. W., 2009. Evaluation of different methods for extracting extracellular DNA from the biofilm matrix. Appl. Environ. Microbiol. 75, pp. 5390-5395.

Why viewing antibiotic resistance genes as a pollutant is a problem

It is not uncommon that scientists, especially researchers active within the environmental field, view antibiotic resistance genes (ARGs) as pollutants (e.g. Pruden et al. 2006). While there are practical benefits of doing so, especially when explaining the threat of antibiotic resistance to politicians and the public, this generalization is a little bit problematic from a scientific view. There are several reasons why this view is not as straightforward as one might think.

The first is that ARGs does not spread the same way as pollutants do. ARGs are carried in bacteria. This means that ARGs cannot readily be transferred into, e.g. the human body by themselves. They need to be carried by a bacterial host (ARGs present on free DNA floating around is of course possible, but likely not a major source of ARG transmission into new systems). Therefore, when we find resistance genes in an environment, that is an extremely strong indication of that we also have resistant bacteria. Also, finding ARGs is not necessarily an indication of high levels of antibiotics, as the resistance genes can remain present in the bacterial genome for extended periods of time after exposure (Andersson & Hughes 2011).

The second reason why ARGs should not be viewed as pollutants is that they are not. If anything, the ARGs contribute to the resilience of the ecosystem towards the actual toxicants, which are the antibiotics themselves. Having a resistance gene is an insurance that you will survive antibiotic perturbations. Calling ARGs pollutants just deflects attention from the real problem to nature’s response to our contaminant.

What we have to do is not to try to defeat the resistance itself, but to try to minimize the spread of it. This means that we need to constantly monitor our usage and possible emissions of antibiotics and try to reduce risk environments as much as possible. Emissions from sewage treatment plants (Karthikeyan & Meyer 2006; Lindberg et al. 2007), hospitals (Lindberg et al. 2004), production facilities (Larsson et al. 2007; Fick et al. 2009) and food production (Davis et al. 2011) are obvious starting points, but we need to continuously monitor sources of antibiotic pollutions. Of course, this is only my view of the problem, but I believe that while the problem for our society lies within the resistance genes, the cause lies within the actual pollutants – the antibiotics we use and abuse.

References

  1. Andersson, D.I. & Hughes, D., 2011. Persistence of antibiotic resistance in bacterial populations. FEMS Microbiology Reviews, 35(5), pp.901–911.
  2. Davis, M.F. et al., 2011. An ecological perspective on U.S. industrial poultry production: the role of anthropogenic ecosystems on the emergence of drug-resistant bacteria from agricultural environments. Current Opinion in Microbiology, 14(3), pp.244–250.
  3. Fick, J. et al., 2009. Contamination of surface, ground, and drinking water from pharmaceutical production. Environmental toxicology and chemistry / SETAC, 28(12), pp.2522–2527.
  4. Karthikeyan, K.G. & Meyer, M.T., 2006. Occurrence of antibiotics in wastewater treatment facilities in Wisconsin, USA. The Science of the total environment, 361(1-3), pp.196–207.
  5. Larsson, D.G.J., de Pedro, C. & Paxeus, N., 2007. Effluent from drug manufactures contains extremely high levels of pharmaceuticals. Journal of hazardous materials, 148(3), pp.751–755.
  6. Lindberg, R. et al., 2004. Determination of antibiotic substances in hospital sewage water using solid phase extraction and liquid chromatography/mass spectrometry and group analogue internal standards. Chemosphere, 57(10), pp.1479–1488.
  7. Lindberg, R.H. et al., 2007. Environmental risk assessment of antibiotics in the Swedish environment with emphasis on sewage treatment plants. Water research, 41(3), pp.613–619.
  8. Pruden, A. et al., 2006. Antibiotic resistance genes as emerging contaminants: studies in northern Colorado. Environmental Science & Technology, 40(23), pp.7445–7450.

From the literature batch…

A random sample of things from this week’s scientific news I think are worth sharing:

Britain is apparently shutting down many of its climate change outreach efforts. I find this very saddening, and see it as an indication of our extreme short-sightedness. We need to put more effort and funding into preserving the environment – not less. In addition, the economic benefits of taking care of the nature around us will probably be much larger than the small sums we save in the short term by not doing anything. We clearly need better incentives to look beyond the next budget and the next election.

The editorial of Nature Reviews Microbiology points the torch on the need for research within basic microbiology, pointing out that “the functions of many genes in the genomes of even the best studied organisms, such as Escherichia coli and Bacillus subtilis, remain unknown. Often these genes do not resemble other, characterized, genes in the databases, allowing for the possibility that interesting new pathways remain to be discovered. (…) if we want to understand how life works at the molecular level, it is crucial to continue and expand basic microbiology research.” I would like to add that a more complete understanding of at least one model organism would drastically increase the accuracy of genome (and metagenome) annotation in new sequencing projects, which today is patchy, to say the least.