Question

Jabari an 84-year-old man is hospitalized for a course of intravenous clindamycin to treat an infected tooth following a root canal procedure. A week later the patient develops profuse diarrhea: no blood is visible in the stool, but lab test was positive for blood. He is running fever with temperature of 101.9⁰ F. Physical examination reveals substantial abdominal tenderness and distension. White Blood Cells are elevated (Neutrophils 91%, monocytes 7%, lymphocytes 2%).

1. What is the microbial agent? Describe the morphology (shape, arrangement, gram reaction) and cultural properties (O2 requirement, biochemical requirements, motility, etc.) for this microbe.
2. Explain the spread or the occurrence for this infection (cause and transmission) and pathogenicity (virulent factors) of this agent relevant to this case study.
3. Describe the diagnoses (source of specimen, lab tests, and results that confirm your microbe) and treatment (name of Rx, what it targets, why/how does it work against this microbe) also include the general management of this patient.

Answer 1

1st question

Answer: Clostridium difficile

Explanation:

The clues to the diagnosis of clostridium difficile are:

1. The patient was treated with clindamycin. Clindamycin is an antibiotic that has activity against anaerobic bacteria and gram-positive bacteria. Clindamycin destroys the normal flora of the colon. This allows Clostridium difficile to grow and colonize the colon.
2. This bacteria releases toxin that leads to mucosal inflammation.
3. This gives rise to fever and profuse diarrhea with abdominal cramps.
4. On abdominal examination, the patient has dehydration, abdominal tenderness.
5. The patient also develops an increase in the level of white blood cells.

2nd question:

• Shape/ arrangement - capsulated rod shape spore-forming. The bacterium is flagellated.The spores are located large oval and subterminal in location
• Gram reaction - Gram-positive
• Oxygen requirements - Anaerobic
• Biochemical requirements -

  • Biochemical test	Reaction
    Catalase	negative
    Indole	negative
    Fermentation of fructose, glucose, mannitol, mannose	Positive
    Hydrolysis of Esculin	Positive
    Gelatin hydrolysis	Positive
    Indole	Negative
    Nitrate reduction	Negative

• Motility - Clostridium difficile is flagellated therefore it is motile.

3rd question:

Occurrence and spread (cause) -

• C. difficile is a normal inhabitant of the colon.
• The presence of normal flora in the colon prevents the pathogenic growth of C.difficile.
• However, due to antibiotic therapy, there is the disruption of the normal protective flora of the colon.
• This gives an opportunity for the C.difficile to grow and colonize the colon.

Pathogenicity:

• Pathogenic strain of C.difficile produces two types of toxins
  1. Toxin A ( enterotoxin)
     1. This toxin attacks the immune cells ( neutrophil and monocytes)
     2. Causes hypersecretion of fluid by stimulating the release of cytokines
  2. Toxin B (cytotoxin)
     1. Destroys the epithelial cells of the colon.
     2. This leads to their necrosis and stimulates inflammation.
  3. Adhesin factor -
     1. Promotes the binding of the bacteria to the colon epithelial cells.
  4. Hyaluronidase
     1. Promotes hydrolytic activity
  5. Spore
     1. Spores help the organism to survive in the hospital for several months.

4th question:

• Source of specimen - stool
• Lab test
  • Stool culture - most sensitive (but results take time)
    • Anaerobic blood agar
    • Egg yolk medium
  • Glutamate dehydrogenase enzyme-linked immunosorbent assay (EIA) - Detects Glutamate dehydrogenase produced by the bacteria.
  • Real-time polymerase chain reaction test (PCR) to detect C.difficile gene toxin
  • Stool cytotoxin test - In this test, filtered stools of the patient are added to cultured fibroblasts. If the cytotoxin is present it will lead to a cytopathic effect on the fibroblasts
  • EIA mediated detection of toxin A and B (slow sensitivity but high specificity - in other words, if the test is negative it doesn't rule out the diagnosis of C.difficile and a repeat test needs to be done.)
  • Latex agglutination test to detect  Glutamate dehydrogenase produced by the bacteria.

Treatment:

General measures:

1. Discontinue the offending antibiotics.
2. Assess the patient's level of dehydration.
3. Correct dehydration by oral or intravenous fluid therapy.
4. Avoid antimotility drugs
5. Prevent excessive fluid resuscitation and it can lead to pulmonary edema.

Specific measures -  

1. Non-epidemic, non-severe infection, and no evidence of colitis - just discontinue the offending antibiotic. The disease is self-limiting and resolves within 48 hours.
2. Mild to moderate cases - Metronidazole (500 mg 3 times a day for 10 days)
   1. Metronidazole in the anaerobic cells gets reduced.
   2. It prevents the nucleic acid synthesis in the bacterium by disrupting the DNA of the bacterium.
3. If the patient is unable to take oral antibiotics. Fidaxomicin
   1. Fidaxomicin binds to the sigma subunit of the RNA polymerase
   2. This terminates bacterial protein synthesis.
   3. This leads to bacterial cell death.
4. Patients with severe infection:
   1. Vancomycin (125 mg 4 times a day for 10 days or can be increased up to 500mg 4 times a day)
      1. Vancomycin binds to the D-alanyl-D-alanine component of the bacterial cell wall.
      2. This prevents cross-linking and elongation of peptidoglycan.
      3. This leads to inhibition of cell wall synthesis
   2. Fidaxomicin - 200 mg two times a day for 10 days
5. Recurrent C.difficili infection - fecel transplantation.