Scientists in England have discovered how a type of Vibrio bacteria can go dormant and then “wake up.”

Vibrio parahaemolyticus is a marine bacterium that can cause gastroenteritis when contaminated raw or undercooked shellfish such as oysters and mussels are eaten.

It is able to turn dormant in poor growth conditions such as cold temperatures and can remain in a state of hibernation for long periods of time before resuscitating. This dormant mode is also known as a viable but non-culturable (VBNC) state.

Vibrio parahaemolyticus usually grows in warm and tropical marine environments but because of rising sea temperatures in recent years it is now prevalent in UK waters during summer months. In the study, the VBNC state was induced in Vibrio parahaemolyticus by nutrient restriction and lowering the temperature to mimic conditions in the environment during poor growth times.

Bacteria able to revive and cause disease
University of Exeter scientists identified a population of these dormant cells that are better at waking up, and have discovered an enzyme involved in the process. Their paper was published in the journal PLOS Pathogens.

Lead author Sariqa Wagley, of the University of Exeter, said most of these bacteria die when they encounter poor growth conditions but sub-populations are able to stay dormant.

“We found that this population has a better ability to revive when conditions improve. Our tests show that when these dormant bacteria are revived they are just as virulent and able to cause disease,” she said.

Findings have implications for seafood safety, as dormant cells are not detectable using routine microbiological screening tests and the true bacterial load, or amount of bacteria, could be underestimated.

Results indicated that particular subpopulations of Vibrio parahaemolyticus can remain in the VBNC state for long periods and can be resuscitated more than two weeks after their formation while a few cells can be resuscitated for up to 50 days.

Dormant bacteria harder to detect
“When they go dormant, these bacteria change shape, reduce respiration activities and they don’t grow like healthy bacteria on agar plates used in standard laboratory tests, so they are much harder to detect,” said Wagley.

“Using a range of tools, we were able to find dormant bacteria in seafood samples and laboratory cultures and look at their genetic content to look for clues in how they might survive for long periods. Our results may also help us predict the conditions that dormant bacteria need in order to revive.”

Researchers used wax moth larvae to assess virulence of Vibrio parahaemolyticus and samples of shrimp to test methods on seafood.

Working with the seafood industry, the Exeter team identified a lactate dehydrogenase enzyme that breaks down lactic acid into pyruvate, a key component of several metabolic pathways, which are chemical reactions in a cell. The findings suggest that lactate dehydrogenase is essential for maintaining bacterial dormancy and resuscitation back to an active form.

The study was partly funded by the Biotechnology and Biological Sciences Research Council (BBSRC), with funding and support from Lyons Seafoods.