Cargo ships are spreading antibiotic-resistant bacteria around the world by carrying dangerous pathogens in their ballast tanks and expelling them near harbours.
When researchers analysed the tanks of nine cargo ships originating from various countries, they discovered 44 species of potentially harmful bacteria in the sediment that accumulates within the tanks. DNA sequencing revealed ten antibiotic resistance genes within the samples. These genes can make bacteria resistant to medical interventions, meaning humans are more likely to die from them.
In 2017, more than 50,000 commercial ships crossed the world鈥檚 oceans. When these ships pull into harbours to shift cargo, they expel or take on water into ballast tanks to provide stability. If this water contains antibiotic-resistant bacteria, these bacteria can travel around the world in weeks.
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Some of the bacteria identified in the study were already dead, suggesting that not all survive the journey from one country to the next. Baoyi Lv, an ocean engineer at Shanghai Maritime University in China, who led the study, points out that most of the harmful bacteria were so-called opportunistic pathogens, which are not dangerous to otherwise healthy humans.
The problem of aquatic lifeforms in ballast water, which can threaten biodiversity, has led to regulation by the International Maritime Organisation. However, G眉l艧en Altu臒, a marine biologist at the University of Istanbul in Turkey, says that rules on where and when ballast water can be expelled from tanks, and how this water should be disposed of, are not consistently applied in harbours.
She says that the transportation of antibiotic resistance genes from harbour to harbour may not be an immediate health risk, but demonstrates how difficult it is to control antibiotic-resistant pathogens in a global system.
鈥淚f one corner of the world is polluted, protecting the other cannot produce a solution,鈥� she says.
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Ecotoxicology and Environmental Safety
