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Assalamu alaikom, and welcome back to another ATP video!
Today we will be talking about Listeria monocytogenes.
It will be short & concise, and we hope you find it beneficial!
Listeria monocytogenes is a gram-positive, rod-shaped bacteria that is responsible for
causing the infection listeriosis.
The disease can affect anyone in the population, however, it’s more common in individuals
with weak cellular immunity like pregnant women, infants, and elderly.
Although the number of cases involving Listeria has decreased in recent years and it’s not
the most common foodborne illness, it’s still quite important to know about the bacterium
as it’s linked to the highest mortality rate.
Approximately 1,600 people get listeriosis each year with approximately 260 people dying
from the disease!
This was just a very brief introduction about Listeria.
Now let us move on and talk about its important features.
Listeria monocytogenes belongs to the class of Bacilli.
And there are currently 10 species that belongs to Listeria, however, only L. monocytogenes
is associated with human illness.
The bacterium is gram-positive, non-spore-forming, facultatively anaerobic, and rod-shaped.
It is catalase-positive and oxidase-negative, and it expresses beta hemolysin which causes
destruction of RBCs on blood agar.
Moreover, it exhibits a characteristic tumbling motility when viewed with light microscopy.
Listeria is acquired by ingestion of unpasteurized dairy products and cold deli meats.
So, it’s primarily a foodborne disease.
Interestingly,Listeria grows very well at cold temperatures, so storage of contaminated
food in the refrigerator can increase the risk of infection.
And this paradoxical growth in the cold is called “cold enhancement”.
As we’ve just mentioned, the bacterium grows intracellularly, and it can move by means
of actin rockets which are filaments of actin that polymerize and propel the bacteria both
intracellularly and across membranes different cells.
All of these special features allow the bacteria to escape the host humoral immunity, or in
other words “the antibody defense mechanism”.
Now, let us move on and talk about the unique virulence factors of Listeria.
So, there are primarily four important virulence factors that enable the bacteria to become
pathogenic.
The first one is called “Internalin” which is a bacterial surface protein that facilitate
its attachment to host cells.
The second and the third ones are Listeriolysin O (LLO) and Phosphatidylinositol-specific
phospholipase C (PI-PLC).
Both help the bacteria to escape from the phagosome into the cytoplasm, thereby escaping
destruction.
And finally, Actin polymerization (ActA) which allows the bacteria to move within and between
cells as we’ve previously explained.
Now, let us move on and talk about the transmission of Listeria.
This mainly occurs by one of two ways.
Either via feco-oral route through ingestion of contaminated food such as unpasteurized
milk, or from the mother to her fetus transplacentally or by vaginal transmission during birth.
Listeria has very important implication in clinical practice.
In fact, throughout the history, several foodborne illness outbreaks have been associated with
Listeria.
It can cause wide variety of symptoms ranging from self-limiting symptoms of gastroenteritis
similar to other foodborne germs, and up to more drastic clinical presentations that include,
yet not limited to, sepsis, meningitis, granulomatosis infantiseptica, and even spontaneous abortion!
As we’ve just mentioned, Listeriosis can cause a variety of symptoms depending on the
person and the part of the body affected.
For example, infection in immunocompetent persons can cause gastroenteritis with symptoms
of watery diarrhea, fever, abdominal cramps and so on.
In pregnancy, however, infection can cause abortion, premature delivery.
And newborns infected at the time of delivery as well as immunocompromised individuals can
develop meningitis, which usually presents with presents with fever, neck stiffness,
headache, altered mental status, and other classic signs of meningitis.
The patient may also demonstrate a positive Brudzinski's or Kernig's sign on physical
exam.
We have discussed many things about Listeria, the question now is how we can diagnose Listeriosis?
Okay, so this is usually done with bacterial culture that grows Listeria from a body tissue
or fluid, such as blood, spinal fluid, or the placenta.
The appearance of colonies with a narrow zone of β-hemolysis on a blood agar suggest the
presence of Listeria.
And the isolation of Listeria is confirmed by the presence of motile organisms
which differentiate them from the other nonmotile bacteria.
Now, let us discuss about the treatment of Listeria.
Well, usually ampicillin is the antibiotic of choice.
An alternative treatment is trimethoprim-sulfamethoxazole if the patient has penicillin allergy.
However, keep in mind that the treatment mainly depends on the clinical presentation, and
it’s not unified among all patients.
For example, Listeria gastroenteritis is usually self-limiting and doesn’t require treatment.
On the other hand, treatment of invasive disease, such as meningitis and sepsis usually consist
of combination therapy.
It is much better to never have the infection at all, so there are steps we can do to prevent
infection.
We’ve discussed earlier in this video the routes of transmission, which were either
the feco-oral way or during pregnancy and delivery.
So, if we can control these two ways of transmission, a huge number of people can be protected!
Starting with simple measure such as proper hand-washing techniques and limiting the exposure
of pregnant women and immunosuppressed patients to potential sources such as, unpasteurized
milk products can aid significantly in prevention of the disease.
And till now, there still isn’t any available immunization against Listeria.
Hopefully, further research can aid in solving the problem.
We’ve reached the end of our video.
And now let us sum up the points that we have discussed today about Listeria.
We’ve said they are gram positive, beta-hemolytic, facultative intracellular rods that exhibit
a characteristic tumbling motility.
They possess number of virulence factors that include, yet not limited to Internalins, Listeriolysin
O (LLO), Phosphatidylinositol-specific phospholipase C (PI-PLC), and Actin polymerization (ActA).
They are transmitted either via feco-oral route or during pregnancy and delivery.
The diagnosis is mainly via gram staining and culturing.
And ampicillin is usually the antibiotic of choice, however, treatment is tailored according
to each case.
And finally, there isn’t available immunization, however, proper hand washing and avoidance
of food sources that might lead to developing Listeriosis a can significantly prevent the
disease.
And that’s it for Listeria.
We hope you found it beneficial!
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