Antimicrobial resistant pathogens in coastal waters

Blog post by Prof Will Gaze

I still swim in the sea, but I’m very selective about where and when I do!

Being able to take advantage of our amazing coastal resources is important. These environments contribute towards our health and wellbeing, our society, and our food production. However, pollution and rising sea temperatures may increase the risk posed by antimicrobial resistant pathogens in our waters.

If pathogens become increasingly resistant to antimicrobial drugs, these types of medication will lose effectiveness. Antimicrobial resistant infections are predicted to be the leading cause of death by 2050, so this is a serious issue that we need to address now. I’m working with BlueAdapt at the University of Exeter, alongside our partners across Europe, to investigate waterborne pathogens, and how they’re affected by environmental change.

My team looks at the interaction between the environment and human health. We’re focusing on antimicrobial resistant microorganisms, that have become difficult (or even impossible) to treat.

What kind of pathogens are we studying?

At Exeter we are focusing on key bacterial species that are really common in humans, like E. coli. We actually carry many so called opportunistic pathogens in our gut and they are usually harmless unless they get into a part of our body they shouldn’t be in, such as into our blood or in a wound. A large proportion of E. coli infections are resistant to one or more antimicrobial drugs, commonly known as antibiotics.

Our research also focuses on Enterococci, which are also found in human faeces and are used as a marker of bathing water quality. We’re also studying the effects of warmer sea temperatures on Vibrio species, which are a group of indigenous marine bacteria that can enter the human food chain through seafood.

Colleagues at Bangor University are looking at viruses including adenovirus, rotavirus, norovirus and hepatitis A, all of which are present in human waste and enter the environment through sewage discharge.

How does this relate to climate change?

In the lab, we’re looking at how antimicrobial resistant pathogens (both bacterial and viral) are affected by changes to their environment. This can be changes to temperature, UV radiation, salinity (how salty the water is) and pH level (is the water more acidic or alkaline). All these factors are affected by climate change.

How do pathogens enter our coastal waters?

While much of our wastewater is treated, some enters the environment through combined sewer overflows untreated. In addition, wastewater treatment varies depending on the technologies used, and does not remove or kill all pathogens.

Many of these pathogens enter our waters through raw or treated sewage discharge (water treatment isn’t necessarily designed to remove pathogens from wastewater). Once the pathogens have entered the environment, environmental changes such as higher temperatures may have an effect on their survival and development of antimicrobial resistance.

For example, many of the bacteria we’re studying aren’t environmental organisms: they’re found in humans or animals. Our bodies have a warmer temperature of 37oC, so the increased environmental temperatures may affect survival of these pathogens increasing exposure risk in coastal waters.

How can we minimise risk to human health?

Improving wastewater treatment and reducing discharge of untreated sewage is a key step in reducing exposure risk in coastal environments. We can all be aware of what we’re flushing down the loo. Un-flushable products like wet wipes can cause blockages in the system, and that can lead to discharges of raw sewage.

It’s also important that we don’t take antibiotics unnecessarily, and don’t put pressure on medical practitioners to prescribe them if you don’t really need them. Those antibiotics are not only driving increased resistance in our own gut bacteria, but they also end up in the environment through the wastewater system.

We also use a lot of other types of antimicrobials in addition to antibiotics, including biocides and disinfectants contained in household cleaners. This means we’re basically putting vast amounts of chemicals with antibacterial properties into the environment. Obviously, we need good hygiene in the home, but there has been a huge increase in the use of antimicrobials across a wide range of consumer goods in recent years.

It’s not just cleaning products that have antibacterial properties: even things like our underwear can be impregnated with antimicrobial chemicals, whoever asked for antimicrobial pants and socks? You can see that after the pandemic there are concerns about hygiene and cleanliness, but increasing use of antimicrobials is likely to result in increased resistance to the critically important drugs we rely on to treat infections.

How can we minimise our own risk to pathogen exposure?

We know that after heavy rainfall, there’s more likely to be raw sewage discharged into the sea and rivers, so there’s guidance that we shouldn’t swim for 48 hours after this. That’s a sensible precaution to minimise our own exposure to waterborne pathogens.

Foodborne transmission can occur if we eat undercooked or raw food, and we need to remember that large amounts of antimicrobials are used in livestock production globally leading to increased antimicrobial resistance in bacteria that live within those animals and can contaminate meat. In some cases river water is used in crop irrigation, so there’s a risk of pathogens entering the food chain through vegetables and salads.

Of course, there’s also person-to-person and healthcare associated transmission of pathogens, and in some cases this will be the most important route, but we should also consider these environmental reservoirs of pathogens and the processes that lead to human exposure and transmission.

How will our research to prevent health risks?

Our team is working to quantify waterborne pathogens including antibiotic resistant bacteria, which helps to inform evidence-based policy making. We need to be able to demonstrate what the risks are, and we’re specifically looking at how climate change affects these risks.

As well as higher temperatures increasing the survival rate of certain bacteria, things like increased heavy rainfall and flooding events will cause more sewage discharges. Other predicted impacts, like changes to salinity and pH levels, will also have effects on the fate of these pathogens.

We have extensive links with industry, regulators and policy makers, in the UK, the EU and globally. We’re communicating with them all the time, and we speak at policy conferences about things like antibiotic resistance and safer seas. We’ve also had conversations with politicians directly about some of these issues, which are very topical. There are lots of different ways we can undertake knowledge exchange and inform policy – it’s a key part of what we do.

Projects like BlueAdapt are about finding solutions that help us adapt to changing health risks as our climate and environment change. As well as attending stakeholder groups and writing papers, we also look at more accessible forms of communication. We’ll keep you updated about our research, both here and on our social media channels.

About me

I’m Will Gaze, a professor of Microbiology at the University of Exeter Medical School, in the European Centre for Environment & Human Health. I’m part of the BlueAdapt team at Exeter, working alongside microbiologists at Bangor University and the University of Galway, as well as colleagues from all of our 12 partners across Europe. I still swim, but I’m very selective about where and when I do!