In the Middle Ages, it killed some 25 million Europeans within a few short years; it served as a symbol of the conflict with the absurd in Albert Camus’ most famous novel; and it still looks much the same today as it did in its earliest appearance back in 1,300 B.C.: the plague, caused by the bacterium Yersinia pestis. Fortunately, thanks to modern-day antibiotics, the days when millions of people fell prey to this dreaded disease belong to the past.

Früher jagte die Pest den Menschen Angst und Schrecken ein. Heute wissen wir, dass Rattenflöhe die Überträger der bakteriellen Infektion waren.

Nevertheless, the plague is not defeated yet. People still get sick from the “Black Death“ – especially in areas with poor medical care. In seven countries – Brazil, the Democratic Republic of the Congo, Madagascar, Myanmar, Peru, Vietnam, and even the US – the plague emerges annually since its statistical recognition by the WHO. The outbreaks in the US have a rather unique background: in the Southwestern United States, populations of prairie dogs are a natural reservoir for the pathogen. If domestic cats capture infected prairie dogs, they can subsequently transmit Yersinia pestis to humans through direct physical contact.

Three diseases – one pathogen

Plague is a disease of rodents and their fleas. A common epidemic in countries with poor sanitation may start with fleas contracting the bacterium from infected rats. The fleas’ bites transmit Yersinia pestis to other members of the rat colony and, when all of the animals in the colony have perished, the fleas jump over to humans instead. Like a lot of primary zoonoses – infections that are directly transmitted from animal to human – plague is a serious disease, causing death in over half of all patients if they are not provided with adequate medical care. There are three different types of plague: bubonic, pneumonic, and septicemic, depending on whether the bacterium infects the host’s lymphatics, lungs, or bloodstream. The pathogen itself however – Yersinia pestis – is always the same.

Research done on a model

Yersinia Pseudotuberculosis
Yersinia pseudotuberculosis

The different species of the Yersinia family use a very similar set of mechanisms to infect its host and spread throughout the host’s body. To investigate the regulatory mechanisms of Yersinia infection, scientists at the Helmholtz Centre for Infection Research are using a slightly less virulent relative of the plague bacterium, Yersinia pseudotuberculosis. One mechanism the researchers are looking at is temperature regulation, which is used by Yersinia to ensure that its infection program is only started whenever an infection attempt is actually promising. The applied virulence mechanisms are energetically highly expensive and therefore only activated at temperatures around 37 degrees Celsius – in other words at a host organism’s normal body temperature. The critical temperature is sensed by Yersinia through a special protein inside the bacterium that employs a molecular thermometer, which is required for infection to assume an “attack-ready“ mode.

Looking ahead

An important mechanism of infection Yersinia shares with other bacteria like Salmonella, Escherichia coli, Shigella, Pseudomonas, and Bordetella is a type III secretion system. Using a nano-syringe, the bacterium injects effector proteins into the host cell, which ensures bacterial entry into the cells, disrupts intracellular communication, and subverts the host’s immune system. HZI scientists are using Salmonella as a model organism for uncovering the mechanisms underlying this type III secretion system.

(Dr Jo Schilling)

Audio Podcast

  • Bakterien mit Thermometer - Vom Kühlschrank in den KörperYersinien machen uns Bauchschmerzen. Wenn wir die Bakterien mit verseuchtem Fleisch zu uns nehmen, infizieren sie unsere Darmzellen und vermehren sich. Aber wie wissen die Yersinien, dass sie nicht mehr in der vergammelten Wurst sind sondern in unserem Körper? Die Antwort ist simpel: Die Bakterien haben ein Thermometer. Hören Sie zu, wie das funktioniert...

Research of the HZI

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