A 56-year-old patient who has been on Meropenem and Fluconazole for six days for intra-abdominal sepsis has developed new fevers and blood cultures have shown a Gram negative organism. The sensitivities are given below:

Gentamicin

Tobramycin

Ampicillin

Imipenem

Ciprofloxacin

Ticarcillin

Gram

negative

bacillus

R

R

R

R

R

R

  • List three likely causative organisms for the new episode of sepsis.
  • For each organism listed give an appropriate antibiotic.

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College Answer

  • Stenotrophomonas maltophilia · Co-trimoxazole
  • Multi-resistant Acinetobacter · Amikacin / Colistin
  • Multi-resistant pseudomonas spp · Amikacin
  • Enterobacter spp - Amikacin
  • Proteus spp - Amikacin

Any other reasonable combination accepted

Discussion

The college recognises the many different ways to skin a cat, and accepts any reasonable combination.

However, the savvy candidate will recognise that imipenem is the specific antibiotic listed there.

There are some Gram-negative bacteria which are intriniscally imipenem-resistant, but which are still susceptible to other carbapenems (provided they are antibiotic-naive). Generally, there are only a few bugs which have an intrinsic imipenem resistance. Specifically, these would include any intracellular organisms, such as Chlamydia.

This list is small, and it also includes organisms which are not relevant to this question.

  • Stenotrophomonas maltophila
  • Pseudomonas maltophilia
  • Pseudomonas cepacia 
  • Enterococcus faecium
  • MRSA

Potentially, one could spew out a list of gram negative bacteria and preamble each name on the list with the words "multi-resistant":

  • Acinetobacter
  • Stenotrophomonas
  • Serratia
  • Klebsiella
  • Enterobacter
  • Pseudomonas
  • Citrobacter

Then, one can add the antibiotics. Most of these bugs will be susceptible to amikacin or colistin.Serratia Citrobacter and Acinetobacter have a particular weakness for co-trimoxazole.

"Any other reasonable combination accepted."

References

References

Giamarellou, Helen, and Garyphallia Poulakou. "Multidrug-resistant gram-negative infections." Drugs 69.14 (2009): 1879-1901.

Falagas, Matthew E., Sofia K. Kasiakou, and Louis D. Saravolatz. "Colistin: the revival of polymyxins for the management of multidrug-resistant gram-negative bacterial infections." Clinical infectious diseases 40.9 (2005): 1333-1341.

Kimberly D. Boeser, PharmD "Are all carbapenems the same?Infectious Disease News, November 2008

Zhanel, George G., et al. "Comparative review of the carbapenems." Drugs67.7 (2007): 1027-1052.

Braveny, I. "In vitro activity of imipenem—a review.European journal of clinical microbiology 3.5 (1984): 456-462.