Evolution of tigecycline resistance in Klebsiella pneumoniae in a single patient.

Carbapenemase-producing Klebsiella pneumoniaeinfections carry serious clinical and infection-controlimplications. Isolates possessing such hydrolyzing enzymes have been described in the United States and around the world. Besides being resistant to carbapenems, they usually confer resistance to fluoroquinolones, piperacillin-tazobactam, and extended-spectrum cephalosporins. Tigecyclinedemonstrates in vitro activity against these organisms, but reported resistance raises concern about tigecyclineuse for these infections. We describe a carbapenemase-producing K pneumoniae evolving resistance to tigecyclinein a 75-year-old male after a prolonged stay in a critical care unit.