Assalamu alaikom, welcome back to another ATP video!
Today we will be talking about Legionella Pneumophilia
Although it will be a short, concise video,
we will cover the most important details related to Legionella.
Let us break down the name first. It is called legionella because it was first identified
at American Legion convention where there was an outbreak of pneumonia amongst the attendees
of the conference. You can easily remember from the name that this bug causes pneumonia.
Legionella is an aerobic, facultative intracellular, bacilli.
Facultative intracellular, if you remember, it means it can grow inside and outside host cells.
Legionella pneuophilia is also: Oxidase and catalase positive
non encapsulated (so it does not have a capsule) and has a monopolar flagellum
Since it is an intracellular organism, it poorly stains with gram stain;
however, it is still considered a gram-negative rod.
Now in the lab, it does not gram stain well which is why we use a silver stain to visualize it. It
has special culture requirements. It is grown on a special agar called Buffered Charcoal Yeast
Extract agar (BCYE) in the presence of Iron and Cysteine which are added to aid in its growth.
Let’s test your memory, or ATP loyalty. Do you remember what other bacteria need the same agar to
be cultured? We said it in our Brucella video ;) The answer is: Brucella, Francisella & Pasteurella
We supplement this agar with antibiotics and silver stain. The antibiotics prevent
other organism form growing and silver stain helps us visualize legionella.
If an immediate diagnosis is required and there is no time for culture,
then a urine antigen test can be done for a rapid diagnosis.
Also hyponatremia can be a helpful clue in patients with suspected Legionella infection
Before we get to its clinical importance it’s time for our surprise quiz
to see if you were concentrating or not! What do we add to the BCYE to culture legionella?
Answer: Iron and cysteine Now moving on
Legionella can cause lobar as well as interstitial (atypical pneumonia). In
addition, it can cause two types of diseases: The first one is called legionnaires disease.
In this disease patient will present to you with mild symptoms and the pneumonia can progress to
a more severe stage if not appropriately managed. So how can we differentiate this from other types
of atypical pneumonia. Well fair not, legionella patients present with 3 unique characteristics.
They will present with a high fever. They will also have GI symptoms like watery diarrhoea,
nausea, vomiting, and abdominal pain. And third, they can have CNS symptoms. These patients may
have hyponatremia which can lead to confusion. Also remember Legionella patients will show
Patchy infiltrate with consolidation of one lobe on x ray. Although this is not always the case
The second disease legionella patients can have, is called Pontiac Fever. This is a
mild form of Legionella infection. It's a type of flu-like illness which is self-limiting.
Patient will present with fever, malaise, fatigue, chills, and headache. These patients, however,
do not develop pneumonia and thus chest radiographs are usually normal.
Now in regards to its transmission, it causes infection due to inhalation
of aerosolized bacteria. However, it is not considered an airborne pathogen. Classically
you will see cases of legionella at hotels caused by contaminated water
aerosols including air conditioning. It can also cause nosocomial pneumonia in nursing homes.
It is worth mentioning that Legionella cannot spread from person to another.
Both Fluoroquinolone or Macrolide can be used for the treatment of Legionella pneumophilia
So things like ciprofloxacin and erythromycin.
As for Legionella prevention, currently we do not have a vaccine for it
However, we can still reduce its transmission
by ensuring that water systems in buildings are well maintained, which include:
Hot tubs, water tanks/heaters, plumbing systems and fountains.
To summarize Legionella is a
facultative intracellular rod, which can also be considered a weak gram-negative organism
Since it does not gram stain well, we can use silver stain to identify it
It can be cultured on BCYE agar it causes Legionnaires’ disease and Pontiac fever
And for the treatment we can use either a macrolide or fluoroquinolone
And that’s it for Legionella, we hope you found it helpful!
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And as always thanks for watching.