A 62-year-old man is evaluated in the surgical intensive care unit for worsening clinical status. Seven days ago, he underwent an exploratory laparotomy for a perforated appendix with peritonitis. Intra-abdominal fluid cultures obtained at the time of surgery grew *Enterobacter cloacae*. He was started on intravenous ceftriaxone based on the following initial susceptibility report:
| Antimicrobial | Susceptibility |
|---|---|
| Ceftriaxone | Susceptible |
| Cefepime | Susceptible |
| Piperacillin-tazobactam | Susceptible |
| Meropenem | Susceptible |
Over the past 24 hours, the patient has developed recurrent fever, tachycardia, and increased vasopressor requirements. His temperature is 39.1°C (102.4°F). Physical examination shows a rigid, tender abdomen. A computed tomography scan of the abdomen reveals a new intra-abdominal fluid collection. The fluid is aspirated, and cultures again grow *Enterobacter cloacae*. Susceptibility testing of this new isolate reveals the following:
| Antimicrobial | Susceptibility |
|---|---|
| Ceftriaxone | Resistant |
| Cefepime | Susceptible |
| Piperacillin-tazobactam | Resistant |
| Meropenem | Susceptible |
Which of the following is the most likely molecular mechanism responsible for this patient's treatment failure?
- AAcquisition of an extrachromosomal element encoding a clavulanate-susceptible enzyme
- BSpontaneous mutation leading to absent outer membrane transport proteins
- De-repression of an inducible chromosomal cephalosporinaseCevap
- DProduction of an intracellular modifying enzyme that acetylates the antimicrobial agent
- EAlteration of the terminal amino acid sequence of peptidoglycan precursors