Method Detects Hypervirulent Bacterial Strains

A recent discovery of hypervirulent Salmonella bacteria has given doctors the means to potentially prevent food poisoning outbreaks from these particularly potent strains.

Previous efforts to find hypervirulent strains were unsuccessful since bacteria behave much like their less-virulent cousins after environmental exposure and it is difficult to assess their virulence during infection, before they switch back to a less-virulent state in the laboratory.

An international team of scientists led by those at the University of California, Santa Barbara (UCSB; USA) examined human clinical Salmonella isolates obtained from fecal and blood samples derived from patients with gastroenteritis or bacteremia, respectively; and animal isolates derived from different outbreaks, individual cases, or surveillance submissions to diagnostic laboratories. The team screened 184 isolates for hyper-infectious strains and performed virulence assays, and bacterial cytocidal activity assays.

Real-time polymerase chain reaction (qPCR) and transcriptome analysis was used to further characterize the isolates. The results of the study indicated that the 14 hyperinfectious Salmonella strains were considerably more virulent than other animal-passaged clinical isolates and the display of increased virulence traits by bacterial strains after murine passage does not necessarily equate to hypervirulence. The strategy to identify hypervirulence was aided by a special medium utilized by the scientists that forces the bacteria to reveal their weapons in the laboratory, which is the first step in the design of therapeutics to combat them.

Douglas Heithoff, PhD, the lead author of the study, said, "These strains exhibit this behavior in the extreme, essentially having a '5th gear' they can switch to during infection. Now that we have identified the problem - and potential solutions - we just need to get to work." Humans usually get Salmonella food poisoning from eating contaminated beef, chicken, or eggs. However, animal waste can contaminate fields where fruits, nuts, and vegetables are grown, thus posing a particular health concern for vegetarians. The study was published online in April 2012, in the journal Public Library of Science Pathogens.

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