Clonal spread of Klebsiella pneumoniae producing CMY-2 AmpC-type β-lactamase in surgical intensive care units

Background and purpose: CMY-2, an AmpC-type β-lactamase, has become more prevalent in Klebsiella pneumoniae isolates at the National Cheng Kung University Hospital, Tainan, Taiwan. This retrospective study investigated the epidemiological characteristics of CMY-2-producing strains of K. pneumoniae. Methods: Molecular experiments were performed to describe the bla_CMY-2 gene carriage rate and the trend of K. pneumoniae isolates with resistance to cefoxitin between January 2001 and June 2003. The epidemiological correlation between patients with bla_CMY-2-positive K. pneumoniae was further analyzed and compared by chart review and pulsed-field gel electrophoresis (PFGE). Results: Of 285 cefoxitin-resistant K. pneumoniae isolates, 69 (24.2%) carried a bla_CMY-2 sequence. The first bla_CMY-2-positive isolate of each patient was genotyped by PFGE; 49 (89.1%) of 55 were genetically related. Forty five isolates (91.8%) were noted between January and September 2002. Eighteen isolates were from patients in 2 surgical intensive care units (SICUs), and 23 were from patients with prior SICU stays. Compared with patients with non-epidemic CMY-2-producing isolates, patients with the epidemic clone had a shorter duration of hospital stay (p = 0.007) and SICU stay (p = 0.01) before isolation. Recent surgery was independently associated with acquisition of epidemic CMY-2-producing K. pneumoniae. Conclusions: An unrecognized clonal spread of K. pneumoniae producing CMY-2 AmpC-type β-lactamase in SICUs was found. Cross-transmission of the epidemic clone, suggested by a shorter hospital stay before isolation of the bacterium and the association with recent surgery, highlights the importance of surveillance to recognize an epidemic and initiate control measures.