Pseudomonas aeruginosa is a organism that causes several different weird clinical manifestations. It’s most known for causing pneumonia, but it can cause your finger nails to turn green, or you could erupt into papules after taking a dip in a hot tub. Let’s get into it.
It is a common cause of pneumonia, and doesn’t have any clinical characteristics to distinguish it from other causative agents. It really likes to cause problems for patients with lung comorbidities like COPD or asthma. It is especially associated with causing problems for patients with Cystic Fibrosis.
We don’t know exactly why yet, but for some reason patients with Cystic Fibrosis are more likely to be chronically colonized with Pseudomonas aeruginosa. The longer that the patient is colonized, the more likely the bacterium will convert to a mucoid version that secretes alginate forming a sticky biofilm. This compounds the mucus problems in patients with Cystic Fibrosis, and is associated with accelerates loss of lung functions. This is why is super important to diagnose the colonization as soon as they happen, even if the patient is asymptomatic.
Pseudomonas aeruginosa is the most common cause of ecthyma gangrenosum which is when an rapidly progressing ulcer forms that appears to scoop into the tissue, forming a crust around the ulcer, and accompanying tissue discoloration and necrosis. This can be caused by other organisms, but P. aeruginosa is the one that’s most associated with it. This is going to look a lot like cutaneous anthrax or pyoderma gangrenosum, so culturing the lesion is going to be key to diagnosis.
The tissue necrosis in skin infections is several different virulence factors like Exotoxin A, which inhibits all protein translation in the host cells causing cell death. Phospholipase C will disrupt the cell membranes causing the cells to fall apart. The most important virulence factor is pyocyanin which releases reactive oxygen species to kill cells. Pyocyanin is also a blue-green color, which will come back to later.
Pseudomonas spp. are the most common cause of otitis externa which presents with ear pain and itchiness.
It can weirdly cause hot-tub folliculitis which is a self-limiting eruption of papules on the skin that was recently immersed in water that usually has low levels of chlorination.
Pseudomonas aeruginosa is a common cause of infection of the cornea especially in patients who use contact lenses, because the plastic provides a perfect little spot for the bacteria to latch on to.
You’re going to rely on culture identification methods to diagnose these infections. One weird thing that can happen is that if you grow Pseudomonas aeruginosa on nutrient agar it can make a huge array of pigments including a blue-green pigment caused by the pyocyanin virulence factor. It can also smell distinctly sweet like grapes.
Treatment is going to really rely on susceptibility results but can typically be a beta-lactam. If you’re trying to treat pneumonia caused by Pseudomonas aeruginosa, you shouldn’t use only aminoglycosides because they perform poorly in an acidic environment of the lung.
A 25-year-old male presents with shortness of breath, sore throat, cough, dyspnea, and chest tightness for the past two days. Vital signs reveal a temperature of 102.2F, blood pressure of 136/91 mmHg, a heart rate of 150 bpm, and an oxygen saturation of 99% on room air. Physical examination reveals that the patient is having difficulty talking while supine. There is peripheral cyanosis and bilateral wheezing. Past medical history is unremarkable, but the patient does live in a crowded living environment with poor sanitation. MALDI-TOF analysis reveal an infection with Pseudomonas aeruginosa. What is the mechanism of action of the virulence factor that causes this organism to produce a blue-green pigment?
A. Inhibits the elongation factor-2
B. Degrades cellular membranes
C. Releases reactive oxygen species
D. Disables inhibitory G proteins
First, diagnose the patient.
This patient is presenting with sore throat, cough, dyspnea, chest tightness, fever, peripheral cyanosis, bilateral wheezing, and tachycardia, which is suggestive of pneumonia.
A. Exotoxin A is produced by Psudomonas aeruginosa and ADP-ribosylates the eukaryotic elongation factor-2 causing a complete stop to protein synthesis within the cell and obviously leading to cell death.
B. Phospholipase C degrades the membranes of cells which will cause the lysis of cells.
C. Pyocyanin releases reactive oxygen species causing the death of many cell types including white blood cells. Like it’s name implies, it is also the reason that Pseudomonas aeruginosa is often a blue-green color on nutrient agar.
D. The Pertussis Toxin from Bordatella pertussis disables inhibitory G proteins causing the disruption of cellular signaling and wide spread issues including inhibiting the action of the respiratory cilia.
Therefore,
Three-days after a birthday party, twenty-five people presented to various area clinics with a new-onset rash. The papular rash covers the trunk and legs of most of the patients, and is typically itchy. After questioning, it was discovered that all of the patients swam at a community pool at the birthday party. Three attendees who did not swim did not acquire a rash. More investigations discovered three more party attendees who swam were diagnosed with otitis externa. What is the most likely causative agent?
A. Parvovirus B19
B. Scabies
C. Type-IV hypersensitivity
D. Pseudomonas aeruginosa
First, diagnose the patients.
The patients are presenting with a puritic papular rash that is clearly infectious in nature, and is probably associated with swimming in the pool. This is hot-tub folliculitis (even if it was a swimming pool and not a hot tub).
A. Parvovirus B19 causes fifth disease or slapped-cheek syndrome. It can also manifest as a lace-like rash that can be intensely itchy, but this is usually completely erythematous without any papule formation.
B. Scabies is a mite infestation caused when the female mite burrows into the skin to lay eggs. You can often see the tracks of the burrows around the lesions. This is an intensely itchy rash, that is definitely infectious, but often has ulcerations and crusting. This is spread through direct contact that has to last about 10 minutes, which is why this is associated with family groups or sexual contact. Which probably didn’t happen in this situation, but I guess it depends on the birthday party…
C. Contact dermatitis could cause a very itchy rash due to contact with an allergen. This is a Type-IV hypersensitivity, and is driven by the T-cell responses. However, this typically presents with a more erythematous rash than a papular rash. It is also highly unlikely that you would have 25 people who are all allergic to the same allergen in one pool.
D. Hot-tub folliculitis is associated with Pseudomonas aeruginosa and forms an eruption of papules that are itchy anywhere on the body that was immersed in the contaminated water.
Therefore,
References:
https://bmcinfectdis.biomedcentral.com/articles/10.1186/s12879-019-3765-1
https://microbewiki.kenyon.edu/index.php/Pseudomonas_aeruginosa
https://www.cdc.gov/mmwr/preview/mmwrhtml/mm4948a2.htm
https://www.aafp.org/afp/2011/0715/p195.html
The Bradley Lab 