Generally speaking, it is inadvisable to eat foods containing Salmonella bacteria – especially if you’re not a fan of diarrhea, fever or abdominal cramps. In the future, however, we might be swallowing genetically-engineered versions of the little guys as a way of treating viral infections. If we do, it will be thanks to research presently being carried out at UC Berkeley’s School of Public Health. Scientists there have reprogrammed Salmonella bacteria to act as harmless transporters of virus-stopping enzymes.
Salmonella was chosen because it has evolved to withstand the human digestive system, so a medication containing the bacteria could simply be swallowed instead of being injected or inhaled. The bacteria is also a good choice because a human-safe strain of it already exists, and is used in the typhoid vaccine. To be on the safe side, however, the Berkeley scientists further engineered that strain, disabling a gene that it requires in order to replicate.
In the study, mice were infected with cytomegalovirus, which can prove fatal to people with weakened immune systems and can cause mental retardation in newborns.
The researchers then cloned ribozymes into the bacteria. Ribozymes are enzymes that are able to target and cut specific RNA molecules within viruses, but they are unable to penetrate infected cells on their own. Salmonella, on the other hand, is very good at doing so. As a control, a separate group of bacteria were cloned with a defective version of the ribozymes, that should not have an effect on the viruses.
When the Salmonella was given orally to the mice, the viral load in the animals that received the bacteria containing the good ribozymes ended up being 400 to 600 times lower than in the mice that received the defective ribozymes, or that received no Salmonella at all. Additionally, the bacteria itself was shown to have no harmful effects.
While viruses themselves can be utilized as vectors for gene therapy, using bacteria should reportedly be much safer, easier and less expensive – while lab-raised viruses must be carefully grown in host cells, bacteria will quickly reproduce on their own when added to a simple medium.
“This study focused on the use of Salmonella and ribozymes to fight infections, but with more research, this method could eventually be used to treat other conditions as well, including cancer,” said virologist Fenyong Liu, who developed the technique along with bacteriologist Sangwei Lu.
The research was published this week in the journal Proceedings of the National Academy of Sciences.