Carbapenem MICs in Escherichia coli and Klebsiella Species Producing Extended-Spectrum β-Lactamases in Critical Care Patients from 2001 to 2009

Extended spectrum β-lactamase (ESBL) -producing Enterobacteriaceae are increasing in prevalence worldwide. Carbapenem antibiotics are used as a first line of therapy against ESBL-producing Enterobacteriaceae. We examined gastrointestinal colonization of carbapenem-resistant-ESBLs (CR-ESBL) among a cohort of critical care patients. In this cohort of patients, we cultured for ESBL-producing Klebsiella spp. and Escherichia coli and then performed MIC susceptibility testing for imipenem, doripenem, meropenem, and ertapenem on the patient9s first isolate. MLST was performed on isolates that were ESBL producing and carbapenem resistant. Among all ICU admissions, 4% of the admissions were positive for an ESBL-positive surveillance culture and 0.64% had a positive CR-ESBL. Among the patient9s first ESBL positive E. coli or Klebsiella spp. surveillance culture, 11.2% were carbapenem resistant. In this cohort of patients, ST 14, ST15, ST42, and ST 258 were the dominant sequence types with ST15 and ST258 steadily increasing in prevalence from 2006 to 2009. Patients colonized by CR-ESBL were significantly more likely to receive anti-pseudomonal, and anti-MRSA (methicillin-resistant Staphylococcus aureus ) therapy prior to ICU admission compared to patients colonized by carbapenem-susceptible ESBLs. They were also significantly more likely to have received a cephalosporin, or carbapenem antibiotic compared to patients colonized by carbapenem-susceptible ESBLs. In conclusion, in a cohort of patients residing in intensive care units within the United States, we found 10% of the isolates were resistant to at least one carbapenem antibiotic. The continued emergence of carbapenem-resistant ESBLs is of significant concern as infections due to these organisms are notoriously difficult to treat.