Identification of CTX-M β-lactamases in Escherichia coli from hospitalized patients and residents of long-term care facilities

Bacteria harboring CTX-M extended-spectrum β-lactamases (ESBLs) have been identified worldwide, with most reports coming from regions outside North America. We have identified CTX-M enzymes in 31% of ESBL-positive Escherichia coli isolates from our hospital and more than half (53%) of the isolates from associated long-term care facilities. Approximately 3/4 of all CTX-M–bearing isolates were from urine specimens, with a predominance of CTX-M-15. A large proportion of such isolates were nonsusceptible to levofloxacin, trimethoprim/sulfamethoxazole, and all β-lactam antimicrobials with the exception of the carbapenems, requiring carbapenem therapy for acute urinary tract infection or urinary tract-related sepsis. CTX-M β-lactamases have emerged within our location, and detection of bacteria harboring these enzymes in the clinical microbiology laboratory remains problematic because molecular methods are needed for their identification.