Ertapenem resistance among Klebsiella and Enterobacter submitted in the UK to a reference laboratory

Abstract The emergence of carbapenem resistance in Enterobacteriaceae represents a major public health concern. We investigated ertapenem-resistant clinical isolates of Klebsiella spp. and Enterobacter spp. referred to the UK's national reference laboratory for antibiotic resistance. Minimum inhibitory concentrations (MICs) were determined and interpreted according to British Society for Antimicrobial Chemotherapy guidelines. Genes for carbapenemases and CTX-M extended-spectrum β-lactamases (ESBLs) were sought by polymerase chain reaction, and imipenem hydrolysis was determined by spectrophotometry with crude extracts. From June 2004 to April 2006, 95 Klebsiella spp. and 76 Enterobacter spp. isolates resistant to ertapenem (MICs >2 mg/L) were received, 40% of which (38 Klebsiella spp. and 30 Enterobacter spp.) were highly resistant to ertapenem (MICs >16 mg/L). Imipenem and meropenem were active (geometric mean MICs