London’s waterways are rife with antibiotic resistant genes.

Tower Bridge.

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The Regent’s Canal, Regent’s Park Pond, and the Serpentine contained high level of antibiotic resistance genes, a new study reports, but none were worse than the Thames. These genes encode resistance to common antibiotics such as penicillin, erythromycin, and tetracycline. They found their way into the water from bacteria in human and animal waste.

Laced waters

“This [study] shows that more research is needed into the efficiency of different water treatment methods for antibiotic removal, as none of the treatments currently used were designed to incorporate this,” says lead author Dr. Lena Ciric from UCL Civil, Environmental and Geomatic Engineering.

“This is particularly important in the case of water bodies into which we discharge our treated wastewater, which currently still contains antibiotics. It is also important to look into the levels of antibiotics and resistant bacteria in our drinking water sources.”

When humans or animals take antibiotics, part of the active substance gets excreted (while still active) into sewer systems and, from there, into freshwater sources. Once there, they’re exposed to bacteria and create an environment that favors resistant microbes. These will multiply faster than their non-resistant counterparts, making the resistance genes more prevalent in the total population. Resistant microbes can also share their resistance with their peers via lateral gene transfer.

The team developed a DNA-analysis method that can be used to measure the quantity of fourteen types of antibiotic resistance genes per liter of water. They then applied it in different water systems throughout London and compared the results. The Thames River had the highest level of antibiotic resistance genes, followed by The Regent’s Canal, Regent’s Park Pond, and the Serpentine. Antibiotics entering the sewer system are diluted through flushing, but even low levels can encourage resistance genes to multiply and spread to more microbes. The Thames is likely to have higher levels of antibiotics and resistant genes because a large number of wastewater treatment works discharge into it both upstream and in London.

The authors note that there is currently no legislation in place which specifies that antibiotics or the genes that encode their resistance need to be scrubbed from water sources. This could mean that antibiotics and said genes could be present in small amounts in drinking water, although this would require testing.

The team is now working on finding a way to remove antibiotics, resistant bacteria, and antibiotic-resistance genes from London’s natural water system using slow sand filtration, which is a form of drinking water treatment. This technique is already in use around the world including at Thames’ Coppermills Water Treatment Works, they explain, which provides drinking water for most of north east London. Their plan is to beef-up this filtration technique by tweaking the properties of the sand and activated carbon used in the filters, and by varying water flow rates.

The paper ” Use of synthesized double-stranded gene fragments as qPCR standards for the quantification of antibiotic resistance genes” has been published in the journal┬áJournal of Microbiological Methods.