Listeriosis: highly virulent strains detected 2

Listeriosis: highly virulent strains detected

Virulent discovery: In China, researchers have discovered a previously unknown germ strain of Listeria monocytogenes, a causative agent of listeriosis. The new strain of bacteria is significantly more aggressive than any known variant of these pathogens so far and apparently some classical tests cannot be detected. So far, these listeria have only been detected in sheep and goats, but animal products can also infect humans.

Listeria is one of the deadliest food microbes known. Again and again people die and die after being infected with contaminated raw dairy products, meat, seafood, or packaged salads. The pathogen, Listeria monocytogenes, can cause severe meningitis, blood poisoning and organ damage, especially in newborns, the elderly and people with weakened immune systems. The mortality rate for this group of patients is up to 30 percent.

Concerns are also worrying medical experts that the number of cases of listeriosis is increasing in Europe and around the world. Common problem: Because listeriosis with severe symptoms can take up to 70 days, the source of contamination can often no longer be clearly identified. This prevents contaminated products from being recalled in a timely manner. In addition, some listeria strains are now immune to disinfectants.

Unusual features

Now is a new cause for concern. An international research team has discovered a hitherto unknown, particularly aggressive, listeria strain in China. "These bacteria are the most ungrateful representatives of these species that we know today," said Yuelan Yin of Yangzhou University and his colleagues. So far, this strain christened HSL-II occurs only in goats and sheep from the remote area. Particularly known is that liisteria infect both animals and humans and are easily spread by animal products.

Further investigation revealed that the new listeria strain has some unusual features compared to the previously known Listeria monocytogenes variants. Thus, this strain cannot tolerate L-Rhamnose sugar, it has a different surface structure and
it also has genetic features, as the analyzes have shown. "These isolates are the only ones known so far that contain gene segments of another type of listeria," the researchers said.


The transmission pathway in Listeria infection and genome presentation of the Listeria hypervirulent strain. © S. Doijad / J. Falgenhauer

Aggressive and difficult to prove

By retrieving these foreign genes, this listeria strain now combines the virulence characteristics of several highly pathogenic types of listeria – making it as virulent as Yin and colleagues explain. Experiments in mice have shown that these pathogens can especially penetrate human gut cells. In addition, they relatively quickly affect other internal organs such as the liver, spleen, and lymph nodes in the abdomen.

Scary: With classic polymerase chain reaction (PCR) tests, this new Listeria variant cannot be enrolled, according to the researchers. "Its unusual properties, especially the phenotype negative for the wound, probably prevented it from being recognized as a member of the Listeria monocytogenes species," say Yin and his team. "As a result, he was neglected."

"Monitoring must be stepped up"

Given the virulence of the newly discovered Lister strain and the ease of transmission through food, researchers are pushing for further intensification of monitoring for such pathogens in the future. "Because listeriosis is a foodborne infection, measures to identify such highly virulent strains are very urgent," says co-author Trinad Chakraborty of Justus Liebig Giessen University.

"The demonstration of a completely new form of pathogenic Listeria monocytogenes in China underscores the need for international collaboration to quickly identify not only multidrug-resistant bacteria but also new threats to food security from highly virulent strains around the world," Chakraborty said.

Finally: By now, the Listeria novel seems to be still struggling with common medicines: "The antibiotic resistance profile has shown that these Listeria are sensitive to most antibiotics," the researchers reported. There was resistance only to the antibiotics clindamycin. (Nature Communications, 2019; doi: 10.1038 / s41467-019-12072-1)

Source: Justus Liebig Giessen University