Research Isolates ‘Hypervirulent’ Salmonella Strains

Researchers at the University of California, Santa Barbara, have identified certain serotypes of Salmonella—among the more than 2,500 strains known to exist—that have the capacity to become “hypervirulent” during the infective process in animals.

“These strains are 100 times more able to cause disease than other strains,” said Douglas Heithoff, PhD, a research biologist at UCSB. “We’re just beginning to learn why, but we believe that a lot of it has to do with their ability to adapt more rapidly to the environment and override certain areas of the immune system.”

After a global survey isolating Salmonella strains from different outbreaks in various parts of the world, Dr. Heithoff and Michael Mahan, PhD, a professor of molecular, cellular, and developmental biology at UCSB, along with colleagues from Australia, tested a large set of those strains in a laboratory animal model.

A key component of the detective work was identifying the strains during the infective process, as Salmonella strains can appear much like their less-virulent relatives after environmental exposure.

“We had a few strains that came out showing this hypervirulent phenotype,” Dr. Heithoff said. Genome analysis demonstrated that the hyperinfectious strains showed altered gene transcriptions in specific regions related to cellular physiology and metabolism as well as those related to classical virulence functions. (The origins of the particular strains that showed the hypervirulent phenotype is proprietary, Dr. Heithoff said; he cannot reveal what parts of the world they came from.)

“These strains so far are pretty much relegated to livestock and have not yet been implicated in human disease to my knowledge, but you don’t wait for that to happen,” said Dr. Heithoff. “So we’re trying to develop livestock vaccines against these strains. In fact, Drs. Heithoff and Mahan have such a vaccine in development now. “It’s very realistic to develop a veterinary vaccine to reduce the load of these bacteria in the short term.”

The findings were published in the April 2012 edition of the open-access journal PLoS Pathogens.

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