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Microscopic Viruses, ‘Good’ Bacteria Could Protect Catfish From Costly Disease
AUBURN, Ala.—It won't be a silver bullet, the researchers say, but new biotechnology being developed and tested at Auburn shows promise in protecting pond-raised catfish from enteric septicemia, a deadly infectious bacterial disease.
The disease, known as ESC, is caused by the bacterium Edward-siella ictaluri. Auburn scientists discovered ESC, as well as the causal pathogen, in 1976 as they analyzed samples of “sick” fish sent to them from ponds in Alabama and Georgia. The disease began to spread in earnest throughout the catfish industry in the ’80s; today ESC costs the industry as much as $60 million annually.
In recent years, a few control strategies such as antibiotics and vaccines have hit the market, but their effectiveness is inconsistent and their high price tags are prohibitive for some catfish growers. In addition, consumers are increasingly calling for a reduction of antibiotic use in livestock production.
The Auburn research team, led by aquaculture epidemiologist Jeff Terhune and environmental microbiologist Mark Liles, aims to find an effective and affordable means of controlling and perhaps preventing ESC. To accomplish that, the Alabama Agricultural Experiment Station scientists are developing naturally occurring microorganisms—specifically, viruses and probiotic, or beneficial, bacteria—that work as biological control agents to reduce the numbers of ESC-causing bacteria in catfish producers' ponds.
These viruses, called bacteriophages or simply phages, target specific bacteria only. Parasitic in nature, a phage attacks a bacterium and, using the energy of the host organism, produces more phages until the pathogen is destroyed and the phages are released to prey on surrounding bacteria. It is a natural process that is completely safe for fish and for human consumers.
The research thus far has met with success, Terhune says.
“We collected water samples from commercial catfish ponds where there had been recent outbreaks of ESC and processed and analyzed those samples,” he says. “To date we have discovered three phages specific to the E. ictaluri bacterium, as well 25 probiotic bacteria that can kill the pathogen.”
A patent is pending on that work.
In the laboratory, meanwhile, the scientists are reproducing the phages and beneficial bacteria they have isolated.
“We are working now to enhance the capability of these biological control strategies to improve the health of channel catfish,” Liles says.
The researchers also are investigating various dosage levels, combination treatments and application techniques, and they are doing that with catfish producers’ bottom lines in mind.
“It is imperative that we determine the most economically efficient way to use these biological control agents,” Terhune says. “This has to be affordable at a commercial level.”
The ready availability of reasonably priced biocontrol products to protect catfish from costly diseases would have a tremendous economic impact on the industry as a whole, but especially one category of producers.
“The fingerling segment of the catfish industry is where you have the most losses from ESC both in numbers of fish and economically,” Terhune says. “Fingerling producers and hatcheries would almost certainly benefit most from this type of treatment.”
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Contact: Jamie Creamer, jcreamer@auburn.edu, 334-844-2783
OFFICE OF AG COMMUNICATIONS & MARKETING
Auburn University College of Agriculture
Alabama Agricultural Experiment Station
3 COMER HALL, AUBURN UNIVERSITY
AUBURN, AL 36849
334-844-4877 (PHONE) 334-844-5892 (FAX)
AgComm@auburn.edu
