A 60 year old female was admitted to the hospital for an abdominal aortic aneury

Question

A 60 year old female was admitted to the hospital for an abdominal aortic aneurysm repair. The patient did welll intraoperatively and was recovering nicely for the first five days post-operation. On the sixth day, she had five bouts of diarrhea and blood was noted on the most recent bout. Her hospital medications included clindamycin.
What is the most likely diagnosis?
What is the next step in management?
What is the most likely causative agent?
What is the most likely pathogen causing this condition?
What is the mechanism of action leading to this condition?
What is the drug of choice use to treat this condition? What is the alternative drug used to treat this condition? What si the mechanism of action for both of these antimicrobials?

Explanation / Answer

1. pseudomembranous colitis 2. stop clindamycin, start rehydration therapy 3. clindamycin 4. clostridium difficile 5. Clindamycin depletes natural gut flora, allowing other bacteria to proliferate, especially c. difficile which produces toxins into the bowel. 6. drug of choice is metronidazole. Vancomycin is the alternate drug used if c. diff is resistant to metronidazole. Metronidazole is selectively absorbed by c. diff then is non-enzymatically reduced by reaction with reduced ferredoxin. This reduction produces metabolites that are taken up into the bacterial DNA and form unstable molecules. Vancomycin will form hydrogen bonds with terminal D-alanyl-D-alanine moieties of the NAM/NAG-peptides. This prevents the incorporation of the NAM/NAG-peptide subunits into the peptidoglycan matrix, the major structural component of gram-positive bacteria cell walls. Vancomycin effectively prohibits the proper cell wall synthesis.

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