Danish scientists uncover clue to Listeria's toughness

Date: Aug-28-2014 Researchers in Denmark believe they have discovered an important clue as to why the

dangerous and highly adaptable foodborne pathogen Listeria monocytogenes - commonly

referred to as Listeria - is so hard to fight.

The researchers studied how Listeria manages to retain the ability to invade cells while at the same time escape the attention of the immune system.

Birgitte Kallipolitis, an associate professor in the Department of Biochemistry and Molecular

Biology at the University of Southern Denmark, and colleagues report their findings in the

journal Nucleic Acids Research.

Listeria, a bacterium that sometimes occurs in unprocessed and processed foods, causes an

infection called listeriosis. Most infections only result in mild symptoms such as fever,

vomiting and diarrhea, which take about 3 days to pass and do not normally require

treatment.

But in rare cases, listeriosis can spread to other parts of the body and cause severe

conditions like meningitis, which is typically accompanied by severe headache, stiff neck and

tremors.

Unborn babies can also contract a listeria infection from the mother via the placenta.

The US Centers for

Disease Control and Prevention (CDC) estimate that around 1,600 Americans fall ill with

listeriosis and 260 die from it every year.

In Denmark - a country with a population some 60 times smaller than that of the US - over the

last few weeks alone, 28 people have fallen ill and 13 have died from listeriosis caused by

eating processed foods bought in supermarkets.

Listeria is notoriously difficult to fight because it is so adaptable

Prof. Kallipolitis says Listeria is notoriously difficult to fight because it is extremely

able to adapt to changes in its surroundings. This was the subject of their study, which reveals

some important clues about how Listeria manages to retain the ability to invade cells while at the

same time escape the attention of the immune system.

For their study, they examined what happens at the microbiological level when Listeria is

exposed to some of the substances known to be challenging to bacteria - such as antibiotics,

bile, salt, ethanol and acid, many of which it encounters in processed and unprocessed foods in

the human body and also in disinfected environments.

Prof. Kallipolitis says, "We knew that Listeria can resist these substances, but we did not

quite know how." She and her colleagues found the bacterium uses various strategies to resist the

substances.

"Generally speaking, Listeria must be described as extremely adaptable. It is constantly aware

of its surroundings and if the environment changes around it. It reacts instantly and has a

number of strategies to withstand threats," she explains.

RNA molecules help Listeria fine-tune response to attack and immune system evasion

Listeria infects host cells by producing special proteins. In order for infection to be

successful, the bacterium must keep the production of the proteins under a certain level - for

above this level the host immune system becomes aware of it and attacks the pathogen.

The researchers discovered that when they exposed Listeria in the lab to the various anti-pathogen substances like bile, salt, ethanol and antibiotics, the bacterium started releasing

special RNA molecules, as Prof. Kallipolitis explains:

"With these RNA molecules the bacteria can adjust how much or how little to produce of various

proteins. For example it can downgrade the production of the protein LapB, which it uses to enter

our cells. If this production is not downgraded, the bacterium will potentially be detected and

fought by the immune system."

The team also found that these same RNA molecules help Listeria keep watch on its cell walls

in the face of danger. Antibiotics work by attacking the cell walls of bacteria. But when

Listeria is exposed to antibiotics, it rapidly detects the assault on its cell walls and sets

about repairing them.

The researchers observed that in the lab, Listeria only produces the special RNA molecules

when exposed to one of the challenging substances. The bacterium did not produce them when there

was no challenge.

Prof. Kallipolitis says this "reveals part of the mechanism behind Listeria's extreme

adaptability."

The team now plans to find out if removing the RNA molecules renders Listeria harmless.

Medical News Today also recently learned how scientists at the Johns Hopkins

Bloomberg School of Public Health in the US have improved our understanding of bacteria's own sophisticated immune

system. They investigated how a molecular machinery known as Cascade, which stands guard

inside bacterial cells, helps them fight off viruses called bacteriophages.

Written by Catharine Paddock PhD

View all articles written by Catharine, or follow her on:

Courtesy: Medical News Today Note: Any medical information available in this news section is not intended as a substitute for informed medical advice and you should not take any action before consulting with a health care professional.