Scientists studying DNA in soil samples from Svalbard in the High Arctic have discovered a surprisingly large number of clinically-important antibiotic resistance genes. In total, 131 antimicrobial resistance genes were identified, while five out of eight sites had abundant multidrug resistance genes (Environ. Int., doi: 10.1016/j.envint.2019.01.034).
The finding is all the more unexpected as the team was seeking a virgin environment to try and establish what a background level of antimicrobial resistance in soil bacteria looks like. ‘We took 40 samples to give us an idea of what the baseline of resistance might look like in nature, but we were surprised by how different the sites were from each other,’ says lead scientist David Graham at Newcastle University. Areas with high wildlife or human impact had greatest diversity of resistance DNA in the soil.
The results show that antibiotic resistance genes are accumulating even in the most remote locations. Included in a number of samples was a multidrug resistant gene called New Dehli strain, first isolated in India.
Some sites had levels of antimicrobial resistance 100 times greater than others, particularly those with elevated levels of phosphorus, a nutrient usually scarce in Arctic soils. ‘There was much greater resistance diversity in sites with strong signatures of faecal matter,’ says Graham, indicating that migratory birds most likely brought the antimicrobial resistance genes, depositing them via their guano.
In the Kongsfjorden area, there are large colonies of little auks, kittiwakes, guillemots, pink-footed geese and barnacle geese. Indeed, the sample site with the highest diversity of resistance genes was adjacent to a large freshwater lake. Graham doesn’t believe one bird from Asia contaminated this Arctic island, but believes that migratory birds can move resistance all over the globe.
‘The problem is nothing to do with the Arctic,’ he explains. ‘Ultimately if you have big cities where antibiotics are poorly regulated, and where there is poor sanitation and lack of water treatment, then those areas are going to become contaminated with resistance genes.’ These resistance genes are likely to get into bacteria that themselves get inside people and local wildlife, which can then be moved on to another location.
‘The most likely source of the resistance genes is from bird droppings,’ agrees Andrew Singer, pollution scientist at the NERC Centre for Ecology & Hydrology, UK. ‘The birds might be able to carry the genes from sources of pollution that are a significant distance from the sampling site. The birds probably acquired the genes from sewage-impacted water.’