Pseudomonas aeruginosa

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Pseudomonas aeruginosa


Introduction to bacteria

Bacterial structure and functions


Pseudomonas aeruginosa


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USMLE® Step 1 questions

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High Yield Notes

17 pages


Pseudomonas aeruginosa

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USMLE® Step 1 style questions USMLE

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A 23-year-old man was admitted five days ago to the burn ward after suffering severe lower extremity burns at work. On admission, the patient was started on prophylactic antibiotics. Currently, temperature is 39 ºC (102.2 ºF), pulse is 120/minute, blood pressure is 98/55, and respirations are 20/minute. Examination of the burn wounds shows blue-green purulent discharge. Microscopic and laboratory examination of the discharge show Gram-negative catalase-positive bacteria. Which of the following organisms is the most likely cause of this patient’s condition?  

External References

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Aminoglycosides p. 188

Pseudomonas aeruginosa p. , 141, 723


Pseudomonas aeruginosa p. , 141


Pseudomonas aeruginosa p. , 141


Pseudomonas aeruginosa p. , 141


Pseudomonas aeruginosa p. , 141


Pseudomonas aeruginosa p. , 141

Exotoxin A

Pseudomonas aeruginosa p. , 130

Fluoroquinolones p. 36

Pseudomonas aeruginosa p. , 141


Pseudomonas aeruginosa p. , 141

Monobactams p. 187

Pseudomonas aeruginosa p. , 141

Nosocomial infections p. 182, 280

Pseudomonas aeruginosa p. , 141

Osteomyelitis p. 177

Pseudomonas aeruginosa p. , 141


Pseudomonas aeruginosa p. , 141

Pseudomonas aeruginosa p. , 141

aerobic organism p. 124

biofilm production p. 127

encapsulated p. 125

exotoxin production p. 130

immunodeficient patients p. 116

multidrug-resistant p. 195

nosocomial infection p. 182

pigment production p. 127

pyocyanin of p. 107

splenic dysfunction and p. 96

UTIs p. 179

Ticarcillin p. 184

Pseudomonas aeruginosa p. , 141


Content Reviewers

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.


Pseudomonas aeruginosa is an aerobic, gram-negative, rod-shaped bacterium commonly found in the environment, such as in soil, in the home, and in hospitals. It is known to opportunistically infect immunocompromised people, and for its multi-drug resistance that is hard to treat.

It is also known to form biofilms that provide it with extra protection against antibiotics on top of its preexisting multi-drug resistance. P. aeruginosa can cause a variety of infections, including urinary tract infections, wound infections, sepsis, and lung infections in people with cystic fibrosis. Treatment for P. aeruginosa infections is with antibiotics, such as aminoglycosides, carbapenems, and cephalosporins.


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