Pseudomonas

CASE 1

• A 6 year old girl suffers 2nd and 3rd degree burns from an overturned pot of boiling water. She is hospitalized for rehydration and wound care, and she is placed on an antibiotic to prevent infection.

• On the 5th day of hospitalization, the nurse notices a fruity odor from some of the wounds when the bandages are removed and replaced. There is pus covering some of more severe burn sites.

• The same day, the patient develops a chill followed by a fever to 38.5 degrees. A blood culture is taken, which grows Pseudomonas aeruginosa on the following day. The isolate is resistant to the antibiotic that the patient has been receiving, so a new antibiotic is prescribed.

• After a stormy course in the hospital and an episode of sepsis with hypotension, the patient survives and is referred for skin grafting of the larger areas of full-skin-thickness burns.

Questions:

1. How did Pseudomonas aeruginosa get into the bloodstream?
2. What was the likely original source of this organism, and how did it colonize the burn wounds?
3. The organism growing on blood or MacConkey agar plates gives off a fruity odor and stains the media a greenish hue. What causes the greening of the media?
4. Is it unusual for Pseudomonas to be resistant to multiple antibiotics? Which antibiotic classes are usually active against it?
5. This organism produces an exotoxin. To what other toxins is it most similar?


 

CASE 2

• A 24 year old woman is treated for non-Hodgkin's lymphoma with cytotoxic chemotherapy. Two after the administration of the principle medications, she develop fever and returns to the hospital. She has no cough, gastrointestinal or urinary complaints, and no rash or skin lesion.

• A physical examination is normal except for the enlarged nodes and spleen that were previously present. However, a complete blood count reveals that her leukocyte count is 200/mm3. She is hospitalized and treated with a broad-spectrum antimicrobial agent, ceftazidime, that is active against Pseudomonas. This is fortunate, becuase two days later, the blood culture obtained on admission is growing P. aeruginosa.

• She continues treatment with the antibiotic for 2 weeks until her absolute neutrophil count reaches 1000/mm3.

Questions:

1. Why did this woman develop Pseudomonas sepsis?
2. Where did the infecting organism likely come from?
3. Is this scenario common among patient receiving treatment for cancer?

• A 16 year old Caucasian male is admitted to the hospital for fever and hypoxia. He has a cough that is occasionally productive of very thick and tenacious sputum. A chest xray reveals patchy opacities in the lungs and dilated bronchi (bronchiectasis).

• The patient has cystic fibrosis and has had numerous similar episodes in the past associated with infection by Staphylococcus aureus and Pseudomonas aeruginosa, among other bacteria. All of his past sputum cultures have contained Pseudomonas.

• A culture of his sputum grows numerous Pseudomonas aeruginosa in colonies that highly mucoid and glistening. The organisms is resistant to all antibiotics except for polymyxin B. The blood cultures are negative.

Questions:

1. What is the relationship between cystic fibrosis and Pseudomonas?
2. The highly mucoid colonial morphology of this isolate suggests that it expresses what virulence factor? How does this virulence factor facilitate the continuing infection with the bacteria?
3. Will this patient's Pseudomonas infection be cured with antibiotics?