The finely serrated teeth of sharks are fearsome enough, now scientists say that even touching the skin of a shark could harm you -- by infection.
Teeth aren't a shark's only weapon; they also harbor deadly, drug-resistant bacteria.
Despite the findings there have been no reported cases of shark-related bacterial infection.
Scientists warn other marine creatures likely harbor drug resistant bacteria as well.
As if rows of serrated teeth and an uncanny ability to smell blood weren't deadly enough, sharks now have a new way to harm unsuspecting swimmers: drug-resistance bacteria.
According to recent research in the Journal of Zoo and Wildlife Medicine, sharks and redfish from shores off of Massachusetts to the Belize harbor colonies of deadly, drug-resistant bacteria like Staphylococcus and E. coli.
While there have been no reported infections from shark-related bacteria, the researchers caution that the growing prevalence of drug-resistant bacteria in all animals, land and sea, is alarming.
"The fact that we found drug-resistant bacteria, regardless of distance from shore or interaction with human influences, warrants concern," said Jason Blackburn, a scientist at Florida Atlantic University and a co-author of the journal article. "These bacteria could be pathogenic."
The Staphylococcus, E. coli and 141 other drug-resistant species of bacteria swabbed from the genital cavity of about a dozen different species of shark and redfish were resistant to not only naturally-occurring antibiotics like penicillin, but also to synthetic drugs like ciprofloxacin and doxycycline. The resistant bacteria were found in sharks that swam close to shore, as well as sharks found far out to sea that should have had no direct interaction with humans.
Some resistance to penicillin is expected; the Penicillium notatum fungus secrets the antibiotic as it grows, and has done so for millions of years. It's only natural that some bacteria would develop some resistance, said Blackburn. But ciprofloxacin and doxycycline were synthesized in labs. So where are sharks and redfish acquiring these drug-resistant genes?
Blackburn doesn't know for sure, but he has a few theories. Drugs given to humans could simply be excreted and eventually find their way into the ocean. Or bacteria in humans could acquire the resistance, be excreted, and then colonize fish that sharks eat, or the sharks, themselves. Some antibiotics are routinely dumped into aquaculture to help prevent infections -- that could be a source for some of the resistance.
To be sure of the source, however, more testing will be necessary, said Blackburn.
However the fish acquired these deadly germs, they don't appear to have any effect on either sharks or humans, said Blackburn, although he notes that his study only looked at how widespread the resistance was, and not about the bacteria's effects (which is the focus of an upcoming study).
A person could have also acquired a mild infection from a shark-related bacteria and shrugged it off as a simple cold. Sharks don't appear to be dying from their deadly residents, and there are no reports of deadly shark-related bacterial attacks.
Nevertheless, the research is cause for concern, says Blackburn. If a person is infected by these bacteria it would be very difficult for doctors to fight off the infection. The numbers of multi drug-resistant bacteria are increasing not only in the ocean but also on land.
Sharks and redfish aren't the only organisms to test positive for harboring drug-resistant bacteria, and aren't likely to be the last. Last year another study found that some species of dolphins also harbor drug-resistant bacteria.
"You don't expect to see multi drug resistance from these animals because they shouldn't be exposed to antibiotics," said Adam Schaefer, a researchers at Florida Atlantic University who co-authored the new study.
The research underscores how widespread the use of antibiotics has become. Schaefer and Blackburn both think they will continue to find more marine organisms that test positive for drug-resistant bacteria.
"These animals are at the top of the food chain; they reflect everything that's going on beneath them," said Schaefer.