Refractory vertebral osteomyelitis due to CTX-M-14-producing Escherichia coli at ertapenem treatment in a patient with a coexisting urinary tract infection caused by the same pathogen.

We report the case of a patient with vertebral osteomyelitis and concurrent urinary tract infection (UTI) in which extended-spectrum β-lactamase (ESBL)-producing Escherichia coli (EC(1)) isolated from urine culture was ciprofloxacin-resistant and ertapenem/imipenem-susceptible. The empirically used oral form of ciprofloxacin was switched to parenteral ertapenem based on the antimicrobial susceptibility. However, vertebral osteomyelitis deteriorated, and despite the disappearance of pyuria and a negative urine culture, ESBL-producing E. coli was isolated from a biopsy of the bony material from the fifth lumbar vertebra (EC(2)) and blood culture (EC(3)) at 10 and 12 days after starting ertapenem, respectively. Ertapenem was switched to imipenem, and defervescence occurred 2 days later; a subsequent blood culture was negative. Genotyping indicated that EC(1), EC(2), and EC(3) were of the same clone, with the ESBL being CTX-M-14. The tested antibiotics had identical minimum inhibitory concentrations against each of these isolates. From the pharmacokinetics/pharmacodynamics points of view, it is reasonable to attribute the ertapenem treatment failure in vertebral osteomyelitis due to ESBL-producing E. coli in this case to the suboptimal ertapenem concentration in the inflammatory bone tissue of the host.