Wild sharks, redfish harbor antibiotic-resistant bacteria

		IMAGE: Mark Mitchell, a professor of veterinary clinical medicine at the University of Illinois, and his colleagues found antibiotic-resistant bacteria in sharks and redfish captured in waters off Massachusetts, Florida, Louisiana... Click here for more information.

Scientists have found antibiotic-resistant bacteria in seven species of sharks and redfish captured in waters off Belize, Florida, Louisiana and Massachusetts. Most of these wild, free-swimming fish harbored several drug-resistant bacterial strains.

The study, published in the Journal of Zoo and Wildlife Medicine, found antibiotic-resistant bacteria in every fish species sampled.

The researchers also found multidrug-resistant bacteria in fish at nearly all of the study sites, said Mark Mitchell, a professor of veterinary clinical medicine at the University of Illinois and a senior author of the paper.

"Ultimately the idea of this study was to see if there were organisms out there that had exposures or resistance patterns to antibiotics that we might not expect," Mitchell said. "We found that there was resistance to antibiotics that these fish shouldn't be exposed to."

Among the animals sampled, nurse sharks in Belize and in the Florida Keys had the highest occurrence of antibiotic-resistant bacteria. These sharks feed on crustaceans, small fish and other animals living in shallow waters close to shore.

Random mutations may account for drug-resistant bacteria in marine environments, Mitchell said, but there is a lot of evidence for a human origin.

"The shark population in Belize, for example, is a big tourist area, so there are people in the water right there," he said. "The sampling site is not far from a sewage plant, and so all those exposures we think are playing a role."

		IMAGE: This graphic shows patterns of antibiotic-resistant bacteria in sharks captured in waters off Belize, Florida, Louisiana and Massachusetts. Nurse sharks in Belize and in the Florida Keys hosted the greatest... Click here for more information.

Sewage also is a problem in the Atlantic coastal waters of the United States, he said. Previous studies have shown that sewage outflows can leak antibiotic-resistant bacteria into the environment.

In the new study, the researchers looked for and found bacterial resistance to 13 antibacterial drugs in the fish. Patterns of resistance varied among the sites.

Bacteria from sharks off Martha's Vineyard in Massachusetts and in offshore Louisiana were resistant to the fewest number of antibiotics, while sharks in the Florida Keys and Belize harbored bacteria that were resistant to amikacin, ceftazidime, chloramphenicol, ciprofloxacin, doxycycline, penicillin, piperacillin, sulfamethoxazole and ticarcillin.

Redfish in the Louisiana offshore site hosted more varieties of drug-resistance than sharks in the same waters. This may reflect differences in their age (the redfish were more mature than the sharks), feeding or migratory habits, Mitchell said.

While the presence of antibiotic-resistant bacteria in sharks and other fish does not necessarily harm them, Mitchell said, the findings point to a growing problem for human health.

"There are estimates of over 100,000 deaths from infections in hospitals per year, many of them from antibiotic-resistant organisms," Mitchell said. "And we're creating even more of these organisms out in the environment. … Unfortunately, as these things collect, there's probably a threshold at some point where there's going to be a spillover and it will start to affect us as a species."

People do eat sharks and redfish, Mitchell said, and now these fish represent a potential new route of exposure to drug-resistant bacteria. Sharks and redfish also are predators, and so may function as sentinels for human health.

"Some people might say, well, a bull shark in offshore Louisiana doesn't really have an influence on my health," Mitchell said. "But these fish eat what we eat. We're sharing the same food sources. There should be a concern for us as well."

This study was the thesis for first author Jason Blackburn, a former master's student at Louisiana State University now on the faculty at the University of Florida. The team included researchers from LSU, the University of Florida, the U. of I. and the University of Southern California.

Editor's note: To contact Mark Mitchell, e-mail [email protected]. The paper, "Evidence of Antibiotic Resistance in Free-Swimming, Top-Level Marine Predatory Fishes," is available here: http://www.bioone.org/doi/full/10.1638/2007-0061.1

Antibiotic-Resistant Bacteria in Sharks

Caption: This graphic shows patterns of antibiotic-resistant bacteria in sharks captured in waters off Belize, Florida, Louisiana and Massachusetts. Nurse sharks in Belize and in the Florida Keys hosted the greatest number and diversity of drug-resistant bacteria.

Credit: Graphic produced by Diana Yates. Photo credits: Bull shark (NSW Department of Primary Industries); Lemon shark (drawing by Robbie Cada); Nurse shark (modified from photo by Joseph Thomas); Spinner shark (image by Dieno); Blacktip shark (modified from photo by Albert Kok); Smooth dogfish (image from U.S. Fish & Wildlife Service).

Three years ago I presented at my GP here in San Pedro with visible sores that were diagnosed as a staphylococcal infection. We believed I had contracted it by kneeling on a sandy coral bottom whilst teaching diving - I remembered a sudden sharp pain but nothing was visible until a sore began to develop at least a month later, followed by rapid escalation.

Over a period of weeks she tried several different antibiotics before she arrived at one that worked, and even then only in massive doses. She said that such infections were common here in Belize, and she typically had two or more new cases a month. And that's just one doctor. The infection recently returned and at the earliest signs I went straight back to the same doctor. She said that the treatment she gave me three years ago no longer works and she had to give me a different antibiotic, which appears to be doing the job - it's ongoing.

In Britain now thousands of patients in hospitals die of infections they contracted inside hospital, and for which there is no longer any guaranteed treatment. There are so many antibiotics floating around in the environment that bacteria are now immune to many of them, and it is often difficult, sometimes impossible, to find a treatment that works.

After a long "honeymoon" period of antibiotics available to treat anything, so that bacterial infections rarely killed anyone, we are now regressing to our original state of what we have become used to regarding as minor infections again becoming serious and all too often fatal. Tuberculosis is once again killing people in Europe. A situation we have created for ourselves by profligate and uncontrolled use of antibiotics.

"....kneeling on a sandy coral bottom..."
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