Tularemia bacterium hibernates and can be traced in terror attacks

According to a new doctoral thesis at Umeå University, Francisella tularensis, the bacterium that causes tularemia, can survive in a dormant state for long periods before causing a new outbreak. The thesis also proposes a method for tracing the bacterium if it is used as a biological weapon. 

"Its potency to become dangerous in small amounts, unfortunately, makes this bacteria an ideal candidate as a biological weapon. Therefore, it is important that we have found a way to trace the origin of different bacterial cultures," says Chinmay Dwibedi, a doctoral student at the Department of Clinical Microbiology at Umeå University and the Swedish Defence Research Agency, FOI.

In one study, the Francisella tularensis bacterium was analyzed in infected people and animals during repeated outbreaks in Örebro County in mid-Sweden. It was then discovered that the bacterial genome remained identical for up to nine years. Furthermore, the bacterium could survive for four years without nutrition in a laboratory experiment. In another study, the researchers could see that the bacterium could migrate several thousand kilometers through continental Europe with little change in its genome.

"The results indicate that there is a natural storage effect for the bacterium that can be compared to a microbial seed bank so that it enters a dormant state between outbreaks before reactivating and causing new infections. It also appears that the bacterium has the ability to migrate rapidly for long distances leaving little evolutionary signals to map its movement," says Chinmay Dwibedi.

In his thesis, Dwibedi shows a promising method that Umeå researchers have developed to trace the bacterium. By enhancing certain genetic signals, it could be seen that some genetic variants and mutations, present in low numbers, benefited from life in the laboratory. These mutations were strategically enriched and could be used as signatures. These bio-signatures made it possible to determine whether an outbreak was caused by natural infection or whether it was, for example, the cause of a terrorist attack in which bacteria had been cultivated in laboratories.

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