Podcast: Of sewage and superbugs

Agar plate

16 September 2014 by Sue nelson

This week in the Planet Earth podcast, Elizabeth Wellington and Greg Amos of the University of Warwick explain how sewage treatment could be helping spread highly drug-resistant bacteria around the environment.

To assist those who find text-based content more accessible than audio, a transcript of this recording is available below.

Sue Nelson: This time on the Planet Earth podcast, the impact of sewage treatment on drug resistant bacteria. I'm Sue Nelson and I am on a bridge above the River Sow, just a few miles away from the University of Warwick campus in Coventry. I am with two scientists whose research relates to a hugely important concern that is currently at the heart of public debate. Recently a public vote took place to decide which one of six scientific causes should be the focus of the ten million pound Longitude prize. It was a difficult choice to make but the winner was antibiotic resistance.

Professor Elizabeth Wellington and Dr Greg Amos are with me and both their work relates to this. Now, the World Health Organisation has warned of a post antibiotic era where drugs no longer work. David Cameron has said that the world could be cast back into the dark ages of medicine. Are we right to be scared?

Elizabeth Wellington: Yes, I think we are, absolutely right, and the whole problem of antibiotic resistance is a significant one that has an impact on healthcare, not only in the treatment of infectious disease, obviously, bacterial disease primarily, but also in the way in which we do operations. We rely on antibiotics and we rely on infusions. When you have a drip before an operation so that clinicians when they open you up can feel secure that they've got protection against any invading bacteria and those bacteria may be opportunists, they are not necessarily renowned pathogens, they may be on your skin like Staphylococcus aureus or they maybe in your gut as simply E. coli. One that gets into your bloodstream can cause septicaemia.

Now in the past we were fine because we had a good range of antibacterial antibiotics that could inhibit these organisms that are found in places that they wouldn't normally be found, such as your bloodstream. The problem now is that they are acquiring resistance genes and mechanisms of resistance to combat these antibiotics and my work is focused really on the reservoir of both antibiotic resistance bacteria and their genes out in the environment, which is why we're out here in the beautiful Warwickshire countryside to demonstrate really to you the areas that are really now regarded from our perspective hazards where they are harbouring large numbers of super resistance antibiotic resistant bacteria and bacteria are incredibly promiscuous, they love to exchange genes and that goes on all the time but the further issue is that pollution will select for these genes in a way in which I think is unforeseen in that the genes are like strings of pearls, they are all located on mobile elements, things that we call plasmids or transposons. These mobile elements can move around and you only need to select for one of those genes to get the element preserved in the population or get it moved then it gives an advantage to those bacteria. Where we have pollution, for example, heavy metals or detergents or we have low levels of biocides then we have problems of selection.

Sue Nelson: Now we're specifically above this river because this was used as part of a project that you were doing. Greg, what was actually done here?

Greg Amos: Our project was basically based around the wastewater treatment plant and looking at the impact that the effluent has on the bacterial communities downstream of the treatment plant. In essence we took samples from downstream of the treatment plant and upstream of the treatment plant and we analysed antibiotic resistant communities and what we found was that there was a significant elevation in the numbers of resistant bacteria downstream of the treatment plant compared to upstream and this wasn't just to old antibiotics this was to new antibiotics such as the third generation cephalosporins and we found that the resistant stream to these antibiotics was CTX-M-15 which is actually the main resistance gene we see in the clinic. Clearly this causes a problem. It could be potential human exposure from activities on rivers such as canoeing, swimming, fishing.

Sue Nelson: So where do you think these bacteria are coming from? Are they specifically from inadequate water treatments or are there other aspects of this which are making a contribution to the situation we've got today?

Elizabeth Wellington: Over a couple of years of sampling we've found genes that were indicative of animal populations, so these would be animals that are used in the food chains such as cattle, so we found CTX-M-1 which is a gene that is often found in cattle, in dairy units. Antibiotics are used for mastitis, so that could be a source. You've got obviously a run off from farms coming into the river. You've got run off from the land and we found, as Greg mentioned, CTX-M-15, which is indicative of human populations where you would have sewage, so it would be coming from resistant bacteria in people's gut. So it would be faeces from humans and also from the food chain, from waste treatment and so on.

Sue Nelson: Why has this happened though? Surely the whole point of water treatment is that chemicals don't get into our rivers?

Elizabeth Wellington: It's not chemicals, it is actually biological pollution that we're seeing and I would say that it because we are not so concerned in our waters with biological pollution. Of course there's a biological oxygen demand which is if you have a lot of waste in a river it will become anaerobic and the bacteria will take all the oxygen, but this is more subtle than that, this is a certain type of pollution which involves genes that are resistant. Those resistant genes can get into other bacteria, indigenous river bacteria, they can get onto the land through using the water in the river as irrigation for food crops and they can colonise wild life, they can colonise animals that are using the water as drinking supplies.

So it is a reservoir that is out there and our work is focused on finding these reservoirs and really linking up, because if you look at a flow diagram of how all these reservoirs link together, you've got human waste from hospitals, it gets more treatment than normal waste but does that treatment reduce the drug resistance gene load. We really don't know enough about this so that is coming into the rivers. Then we've got, obviously, sewage treatment. Is it adequate to reduce the load of drug resistance genes? Clearly we've still got an issue there and then we've got the use of antibiotics in farming and as we know a huge amount of antibiotics have to be used to safeguard the welfare of animals and that's a critical point, but can we alternate the way in which we use antibiotics in farming and in human medicine?

Well, obviously, we're trying hard in human medicine but what is being done in animal rearing and of course there are things like changing husbandry, reducing the reliance of antibiotics and trying other methods like probiotics, like feed additives, vitamins. So we need to work harder I think to reduce the environmental load of antibiotics and antibiotic resistant bacteria so that we can reduce the cycle, and the work that Greg also did with me and a number of other colleagues was to look at the Thames catchment as a whole and try and model the inputs from farming and from waste water treatment to see if we could predict what the load for resistance would be and I think we've made a model which we've been testing now and we want to know introduce mitigation strategies.

So, for example, we've got this soakaway system, the SUD system which can reduce the load. There are lots of types of treatment plants that can improve treatment and of course farms can use anaerobic digestion and other kinds of reed beds and those kinds of techniques. So we need to consider the environment as a reservoir for resistance genes as well as the clinic and we also need to worry about humans and the human population carrying a time bomb in their guts which would be the acquisition of drug resistant symbionts or mutualistic bacteria that we can carry on our skin, up our nose, in our stomachs, in our bowels, if they acquire resistance they are the ones that tend to cause us septicaemia as our own bacteria is getting into places and then we can't treatment them

Sue Nelson: It sounds pretty depressing and I know you are giving some hope there but, Greg, what you found with all the samples was it worse than you had expected.

Greg Amos: I don't think really before our work and the work of Professor Wellington's group people hadn't really considered the environment very much as a reservoir for resistance. This was really one of the first studies to prove that resistance genes do come out in the effluent and we were really shocked to see the number of resistance genes in in comparison to a pristine river. I mean a massive, massive escalation of a number of resistance genes and it wasn't resistance genes in inane bacteria, a lot of them were found in E. coli, sequence type 131. E. coli has now overtaken MRSA as one of the main nosocomial pathogens, that and the related Klebsiella pneumoniae is predicted to become the next super bug, so finding them in the environment is definitely a cause for concern.

Sue Nelson: So do you think, Liz, that any of the ten million Longitude prize will find its way to you?

Elizabeth Wellington: Well I really hope so because the environment is something that we need to protect. It is going to be good for us. It is going to be good for animals in the food chain and it is going to be good for the wildlife, for all of us. If we can focus on at least some of that effort can go into protecting our environment we have to look at the round. We have to look at waste treatment, we have to look at agricultural, food processing in industry and which is why the work that NERC scientists do is so important because we're looking at the bigger picture and how things all link together.

Sue Nelson: Professor Elizabeth Wellington and Dr Greg Amos, thank you both very much indeed and that's the Planet Earth podcast from the Natural Environment Research Council. You can follow us on Facebook and Twitter where we will post some pictures of today's recordings. I'm Sue Nelson - thanks for listening.