Pseudomonas aeruginosa


Learning medicine is hard work! Osmosis makes it easy. It takes your lectures and notes to create
a personalized study plan with exclusive videos, practice questions and flashcards, and so
much more. Try it free today! Pseudomonas aeruginosa, or P. aeruginosa,
is a gram-negative bacterium that is abundant in the environment. It tends to opportunistically infect high-risk
individuals, and is well known for its multi-drug resistance, making it hard to treat. P. aeruginosa is an encapsulated, gram-negative,
rod bacterium, that’s an obligate aerobe, so it uses oxygen for metabolism through cellular
respiration. It does not ferment lactose and does not make
spores; but it’s catalase, citrate, and oxidase positive. It has a flagellum, kind of like a tail, at
one end for motility; and has multiple hair-like appendages, called pili, all over that help
with adhesion to other cells. It also has a number of multidrug efflux pumps
that efficiently pump medications out of the bacteria making it resistant to a variety
of antibiotics. In addition it’s able to make beta-lactamases
that degrade beta-lactam antibiotics as well as aminoglycoside-modifying enzymes that alter
aminoglycoside antibiotics – rendering them ineffective. In short, it’s defenses are strong. P. aeruginosa is everywhere in the environment
– in soil; in the home, and in hospitals – where it’s found on improperly cleaned medical
equipment and devices, various surfaces, and on the hands of health care workers. It can survive for months on dry surfaces
and inanimate objects – but particularly loves humid or wet conditions; like hot tubs,
contact lens cases, catheters, and medical ventilators. Transmission can occur when broken skin or
mucous membranes come in contact with contaminated surfaces; or when aerosols containing P. aeruginosa
are inhaled after an infected person coughs or sneezes. Now, a P. aeruginosa infection is actually
not too common in the general population. It’s an opportunistic bacterium, meaning
that it frequently causes infections in high-risk individuals like those with cystic fibrosis,
chronic granulomatous disease, and type 2 diabetes mellitus. It’s also common among individuals with
an immunodeficiency; IV drug abusers, or those with severe burns or deep wounds. P. aeruginosa produces several virulence factors
to help it invade epithelial cells and survive an attack from the immune system. First, there’s endotoxin, a molecule that’s
made up of a lipid and polysaccharide. The endotoxin sits on the outer membrane of
the bacteria, and it’s recognized by the immune system as being foreign and causes
a really strong immune reaction that can cause extensive damage to the host cells. Certain strains of P. aeruginosa also produce
a mucoid exopolysaccharide capsule, and this contributes to the formation of a biofilm
– a slimy, sticky, gummy material – that surrounds colonies of P. aeruginosa and acts
like a shield to protect the bacteria from immune cells as well as antibiotics. P. aeruginosa can also produce toxins that
can be injected directly into the host epithelial cells through a type III secretion system. It’s kind of like a fine needle that pierces
the host cell and forms a tunnel between the P. aeruginosa and the host epithelial cell,
allowing toxins to pass through. P. aeruginosa also releases toxins into the
extracellular environment. For example, it releases phospholipase C which
is an enzyme that degrades the host cell membrane causing the cell to lyse. Other secreted toxins have to move within
the cell to act. For example, exotoxin A is released by P.
aeruginosa into the extracellular environment and then taken up by nearby host cells where
it targets ADP-ribosylation of elongation factor 2, which is a ribosomal protein. That inactivates protein synthesis and eventually
leads to cell death. Pyocyanin is another example. It’s a blue pigment with a sweet, fruity
smell like grapes that’s released by P. aeruginosa and taken up by nearby host cells,
where it generates reactive oxygen species that cause oxidative damage and cell death. In the environment, pyocyanin is released
by P. aeruginosa and it’s taken up by microbes that are competing for nutrients and space,
and causes them to die as well. A sweet fruity death. P. aeruginosa also secretes pyoverdine, a
green compound that is an iron-chelator, that binds to iron and transports it into the P.
aeruginosa. Symptoms of a P. aeruginosa infection depend
on the site of infection. Usually there’s a fever; an elevated respiratory
and heart rate, and an increased white blood cell count. If the infection is in the blood it can lead
to septic shock. But there can also be localized infections,
like an infection of hair follicles, called hot tub folliculitis, can look like a red,
pimpley rash. Burn or deep wound infections can have a blue-green
color and a fruity grape-like smell, and immunocompromised individuals can develop a skin condition called
ecthyma gangrenosum that begins with blisters but rapidly progresses to tissue necrosis. People who use catheters can develop urinary
tract infections and those with infections involving contact lenses can develop conjunctivitis
and eye pain. Individuals with diabetes can develop osteomyelitis,
an infection of the bones – classically from a puncture wound through a moist sneaker insole. It can also cause malignant external otitis,
an infection in the ear canal – sometimes called “swimmer’s ear”. Pseudomonas can cause tricuspid valve endocarditis
particularly in IV drug abusers. And finally, individuals with cystic fibrosis
can have pneumonia – particularly involving the formation of biofilm. Diagnosis usually involves a complete blood
count, as well as cultures of the site of infection – like the blood, sputum, or skin. In terms of treatment, some cases, like Pseudomonas
folliculitis are typically self-limiting, so no treatment is usually necessary. But in more serious infections, cultures and
antibiotic susceptibility testing often guides treatment. Topical antibiotics can be used for superficial
infections; and aerosolized antibiotics are frequently used for lung infections. In severe cases, especially in immunodeficient
individuals, a combination of anti-pseudomonal drugs is needed to overcome multi-drug resistance;
like β-lactam with aminoglycoside; or carbapenems with quinolones and aminoglycosides. So, to recap: P. aeruginosa is a gram-negative
rod bacterium that is ubiquitous in the environment. Virulence factors contribute to key features
of a P. aeruginosa infection including blue-green color, fruity grape-like smell, and formation
of biofilms which add extra protection to P. aeruginosa on top of its already notable
multi-drug resistance. It can cause a variety of diseases from hot
tub folliculitis, to ecthyma gangrenosum, osteomyelitis and malignant external otitis,
and also causes pneumonia in individuals with cystic fibrosis. Definitive diagnosis is made by cultures,
and susceptibility data help identify effective antibiotics.

11 Replies to “Pseudomonas aeruginosa”

  1. As a medstudent you will see pseudomonas infections all the time during your rotations. So pay attention during this video 😏👍

  2. This popped up in my subscriptions, hit a little to close to home (I have a kid with cystic fibrosis). Used to look at these videos for nursing school. Didnt ever think Id be on "the other side" 😛

Leave a Reply

Your email address will not be published. Required fields are marked *