Rectal swabs taken from surfers and bodyboarders indicate that people who regularly recreate in the waters off the UK coastline may be three times more likely to harbor antibiotic-resistant (AR) bacteria in their intestines than those who stick to dry land.
Researchers from the University of Exeter Medical School compared samples of fecal matter from 143 frequent surfers or bodyboarders (at least 3x per month) to 130 volunteers who had low exposure to seawater (no more than once per month). Their microbiological analysis, published in Environment International, showed that 9 percent of surfers were carrying strains of E. coli that cannot be eliminated by the common antibiotic drug cefotaxime. In comparison, only 3 percent of non-surfers tested positive for these species.
"We looked for a particular type of E. coli (E. coli ST131) that is highly virulent and resistant and is spreading worldwide,” lead author Dr Anne Leonard told IFLScience. “It typically causes extra-intestinal (i.e. not gastrointestinal) infections such as urinary tract infections.”
“People taking part in the study who were carrying these bacteria were probably asymptomatic, and therefore they will not need treatment to get rid of these bacteria,” Dr Leonard continued. “However, there is the potential for anyone carrying resistant bacteria to pass them onto other members of the community that they come into contact with... and therefore [put them] at increased risk of developing an infection that is difficult to treat."
Perhaps more troublingly, Dr Leonard’s team found that surfers’ bowels were four times more likely to contain bacterial species with a mobile gene element that confers resistance to cefotaxime and other agents. Bacteria use mobile genes in the form of circular DNA molecules to rapidly share the spontaneous mutations that enable them to survive the effects of antibiotics, leading to overall decreases in the efficacy of antibiotic drugs and the creation of deadly "superbugs". These genetic swaps can occur between members of the same species or wildly different bacterial classes.
Species of terrestrial bacteria with acquired resistance to man-made drugs have been introduced into the waters through large-scale agricultural runoff, sewage, and trash dumping. The ocean is now a major reservoir of dangerous AR bacteria, such as E. coli, that can transfer resistance genes to native species or directly infect an unlucky host who is exposed to seawater – like a surfer.
The team’s current paper came from a larger environmental and epidemiological investigation into AR bacteria in the ocean, called the Beach Bums Survey, that identified surfers to be at higher risk than other aquatic enthusiasts. Essentially, surfers and bodyboarders wipe out more spectacularly than people doing other sports, and infected seawater rocketing down one's throats can easily lead to resistant bacteria colonizing their guts.
These particular surfers, who were chill enough to volunteer for anal swabbing in the name of science, mostly frequented beaches in the southwest of England, Wales, and Northern Ireland. But if you’re hoping to avoid virulent bacteria by surfing elsewhere, remember that AR bacteria are widespread in coastal waters; according to Dr Leonard, there is no reason to believe the areas studied pose a greater risk than other regions.
And even if you plan on avoiding the water entirely, this study highlights a concerning new avenue by which the global crisis of antibiotic resistance may spread.
Study supervisor Dr William Gaze told IFLScience that the aim of the Beach Bums Survey is to assess how resistance evolves in the environment, how bacteria are spread through pollution, and how this can result in transmission to humans.
"Although much investment has occurred to improve coastal water quality, the fact that it ultimately receives all municipal and agricultural waste water means that it still suffers from microbial pollution. The UK produces 11 billion liters of waste water a day that all end up in coastal waters," said Dr Gaze. "Even with treatment of nearly all human waste, this still results in measurable levels of antibiotic resistant bacteria."