New Discovery Treats Antibiotic-Resistant Bacteria

A new scientific discovery soon could provide an alternative to antibiotics for treating bacterial infections in horses. In the September issue of Nature, microbiologists at the University of California, Los Angeles, reported that bacteriophages--viruses that infect bacteria--can be genetically engineered to seek out and destroy specific types of disease-causing bacteria.

At a time when antibiotic-resistant bacteria are becoming increasingly common and tougher to treat, the discovery is welcome news to veterinarians and horse owners. According to the Centers for Disease Control and Prevention, virtually all disease-causing bacteria in the world are becoming resistant to the antibiotic treatment of choice.

Bacterial resistance can develop whenever antibiotics are administered. Once exposed to a particular antibiotic, bacteria begin to "outsmart" the drug by undergoing mutations that make them impervious to it. Mutations are quickly transferred to future generations and to other types of bacteria, making them harder to control.

Jeffery F. Miller, PhD, professor of microbiology at UCLA and lead investigator of the recent study, says that bacteria can't outsmart bacteriophages quite so easily. "As a bacterium mutates in an effort to become resistant," Miller explained, "the bacteriophage mutates along with it, so that it can still kill the bacterium."

A bacteriophage works by latching onto a disease-causing bacterium and injecting its genetic material into the organism. Under the control of the injected genes, the bacterium begins mass-producing bacteriophage offspring.
Eventually, the offspring are so numerous that they burst out of the bacterium, killing it in the process. Newly released bacteriophages repeat the cycle, until the disease-producing bacteria are completely eliminated.

Miller predicts that in time, scientists will engineer bacteriophages capable of destroying virtually every type of disease-causing bacteria. "Depending on the nature of the infection," Miller said, "these new antimicrobial agents could be administered in the form of injections, pills, or ointments, with very few side effects."

Rustin Moore, DVM, PhD, director of the Equine Health Studies Program at Louisiana State University, notes that the use of bacteriophages could have an important impact on the future practice of equine veterinary medicine. "Antibiotic resistance is a big problem, and it can complicate the treatment of infections," he said. "Horses at greatest risk are those that are hospitalized or housed in equestrian facilities where antibiotics are routinely used."

According to Moore, pathogens most resistant to commonly used antibiotics include gram-negative organisms responsible for causing pneumonia, umbilical abscesses, and septic arthritis in adult horses and foals. Gram-positive Staphylococci, often implicated in infections of the skin and joints of horses, frequently are resistant to several types of antibiotics.

Moore believes that it will likely be a few years before bacteriophage technology is implemented in veterinary medicine. "When it is," he said, "it will help veterinarians effectively treat the ever-increasing problem of antibiotic-resistant bacteria in animals."

In the meantime, Moore cautions horse owners to use antibiotics judiciously, and only with a veterinarian's guidance. "To reduce the likelihood of creating resistant strains of bacteria," he said, "it's important for all of us to use antibiotics correctly."

About the Author

Rallie McAllister, MD

Rallie McAllister, MD, grew up on a horse farm in Tennessee, and has raised and trained horses all of her life. She now lives in Lexington, Ky., on a horse farm with her husband and three sons. In addition to her practice of emergency and corporate medicine, she is a syndicated columnist (Your Health by Dr. Rallie McAllister), and the author of four health-realted books, including Riding For Life, published by Eclipse Press and available at or by calling 800/582-5604.

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