Clinical characteristics and molecular epidemiology associated with imipenem-resistant Klebsiella pneumoniae.

Eight patients were infected or colonized with imipenem-resistant Klebsiella pneumoniae (IRKP) from December 1994 to November 1995. Initial Klebsiella isolates were susceptible to imipenem but resistant to all cephalosporins, aminoglycosides, and beta-lactam inhibitor combinations. All patients had been in the surgical intensive care unit and had undergone abdominal surgery or tracheostomy during hospitalization. The average age of the patients was 71 years (range, 41-81 years). All patients were treated with imipenem for 5 to 36 days, and IRKP was recovered from each during or after therapy. Pulsed-field gel electrophoresis (PFGE) of the IRKP isolates revealed three distinct clonal patterns. Paired sequential isolates of imipenem-susceptible K. pneumoniae and IRKP from two patients had identical PFGE patterns, suggesting the development of clonal stepwise resistance to imipenem during therapy. Thus, imipenem resistance in Klebsiella may occur when this agent is used for treatment of infection due to ceftazidine- and aminoglycoside-resistant strains.