It is late Friday afternoon and a new medical intern assumes the care of 2 patients with gram-negative bacteremia in the intensive care unit. Both patients have been empirically treated with piperacillin-tazobactam and remain critically ill. The microbiology laboratory updates the culture results as Enterobacter cloacae complex for the first patient and Serratia marcescens for the other. At this point, the intern vaguely recalls the SPACE or SPICE acronyms (SPACE: Serratia , Pseudomonas , Acinetobacter , Citrobacter , Enterobacter ; SPICE: Serratia , Providencia , Indole-positive Proteus , Citrobacter , Enterobacter ), but after a quick literature search, realizes that neither provides a clear answer as to which organisms are included. Even more perplexing, the available primary literature demonstrates conflicting data for optimal treatment. More confused than ever, the intern calls his infectious diseases colleagues with a series of questions: Are these really AmpC-producing organism