Mycoplasma

CASE 1

• A 16 year old girl has had mild fever, headache, and a dry cough for the past week. In spite of empiric treatment for malaria at the onset of the illness, she continued to have fever. During the subsequent days, she began to produce small amounts of thin, clear sputum.

• The patient is a senior secondary school student from Kumasi. She reported that two of her roommates experienced similar illnesses during the past month.

• She visited the outpatient clinic at the Komfo Anokye Teaching Hospital where her temperature was 38.2 degrees and she was noted to have audible crackles in the left lower lobe of the lung.

• A blood count, sputum Gram stain, and chest xray were performed. Her white blood cell count was 8,300/mm3 with a normal differential count. The sputum examination showed a few neutrophils but no bacteria. A chest xray showed a patchy infiltrate corresponding to the auscultatory findings in the left lung.

• An enterprising medical student, who had been reading extensively on this topic, retrieved the tube of blood that was draw for the blood count (collected in a tube with EDTA as an anticoagulant). She then placed the tube in glass of chipped ice. Within a few minutes, she noted that the blood cells began to agglutinate into small clumps that could be seen with the naked eye. When she warmed the blood back to her own body temperature, the clumps disappeared. She then informed the resident that the patient had mycoplasma pneumonia.

• The patient was treated with a course of oral azithromycin and improved rapidly.

Questions:

1. What organism caused this episode of illness?
2. If the patient acquired this illness from one of her roommates, how many days or weeks ago was the roommate ill? How was the illness transmitted?
3. In which part of the respiratory system does this pathogen normally attach itself? How does it attach, how does it cause local damage, and how does its localization affect the appearance of the xray?
4. Why were no bacteria seen on the sputum Gram stain? Is mycoplasma Gram-positive or Gram-negative? How do we know?
5. What was the significance of the erythrocyte clumping when the tube of blood was paced on ice?
6. Treatment of this pneumonia with ampicillin or ceftriaxone would have been ineffective. What feature of mycoplasmas makes these antibiotics ineffective?
7. What other organ system is infected by other species of mycoplasmas and (related) ureaplasmas?