Antibiotic-resistant bacteria discovered in two Canterbury rivers

Wednesday, 19 December 2018

Samples taken from the Selwyn River showed 'disturbing' amounts of E coli contamination. (File photo)

An antibiotic-resistant E coli strain has been found in two Canterbury rivers, a discovery that could have far-reaching consequences for human health in the future.

Canterbury District Health Board clinical microbiologist Dr Joshua Freeman says news an antibiotic-resistant E coli and other E coli strains are now in the Ashley, Selwyn and Rangitata rivers means it is time for a national survey of just what human health-threatening bacteria are in our livestock.

The antibiotic-resistant E coli was found in samples taken from the Rangitata River (pictured) and also the Selwyn River.

The Fish and Game New Zealand finding was the first time he had heard of antibiotic-resistant cTXM genes in E coli in New Zealand rivers, he said.

Those genes were found in the Selwyn and Rangitata rivers in September.

Sediment found in the Ashley River during the survey.

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'We know these can confer resistance to a lot of antibiotics – penicillin products – in hospitals and communities. That takes out a huge range of workhorse antibiotics and leaves us with second-tier antibiotics

'That raises the question – to what extent do people get exposed to these? We know at the moment that these things come into New Zealand from overseas.'

The last livestock bacteria survey was about 10 years ago, he said.

'We didn't find much at the time. This suggests the landscape has changed.'

The river sampling was undertaken after anglers raised concerns about the risk of infection due to river pollution and the increasing number of dairy cows in Canterbury.

Water was collected from the Ashley, Selwyn and Rangitata rivers in May and September and tested by Massey University's school of agriculture and environment.

The results showed the rivers contained E coli, antibiotic resistant E coli and a dangerous strain of bacteria called shiga toxin-producing E coli or STEC.

STEC infection can cause severe gastroenteritis, including bloody diarrhoea and kidney failure.

The two most common E coli strains found in the testing only come from ruminants, such as cows.

Fish and Game said the test results showed the harmful organisms were present at levels that could impact on human health.

University of Otago, Wellington, department of public health professor Michael Baker said about a quarter of people affected by the shiga-toxin E coli had to be hospitalised.

About 10 per cent contracted hemolytic uremic syndrome, a potentially life-threatening condition that could damage the kidneys.

It was more difficult to know the impact of the antibiotic-resistant E coli strain.

'Antibiotic resistance only matters if you need to be treated with antibiotics. If you went to hospital for a procedure, you might need the antibiotics and then suddenly that would matter. It's an issue we need to think about.'

Dairy cattle put 250,000 tonnes of untreated effluent into our environment every day in New Zealand, Baker said.

'That all has to go somewhere.

'We really do have a major health hazard there to manage. We have to weigh that against it being a major industry here.

'It's disappointing now that we have another thing to worry about, rather than enjoying our freshwater rivers and swimming holes. As a New Zealander, I find it really disappointing.'

Canterbury medical officer of health Dr Alistair Humphrey said the concern was antibiotic-resistant cTXM genes could spread from one bacteria to another.

'Then there will be some infections that cannot be treated if the population of bacteria that cause the infection become antibiotic-resistant.'

Precautions regarding swimming in the region's rivers and lakes remained the same: check the Environment Canterbury (ECan) water quality website, don't swim for 48 hours after heavy rain, and wash your hands scrupulously.

'Our rivers are getting dirtier, even with our farmers being as compliant as they are meant to be. We have got too many cows.'

ECan chief scientist Dr Tim Davie said the regional council took any study showing the presence of E coli in rivers and streams seriously.

'STEC are derived from ruminant mammals, including both sheep and cattle, and can be ingested by humans through contact with animals or swallowing infected water.

'We manage this risk through stock exclusion rules as well as encouraging fences and buffer strips at the edges of rivers and streams to prevent stock excrement entering the water.'

There was 'urgent need' for research into the health risks associated with differing concentrations of STEC and other pathogens in the waterways.

ECan monitored E coli and algal levels every week at 50 popular freshwater swimming sites around Canterbury.

Fish and Game New Zealand chief executive Martin Taylor said the results were disturbing.

'In plain language, the results indicate swimming in these rivers could be like playing Russian roulette with the health of you and your family.'