In vitro activity of ceftiofur tested against clinical isolates of Escherichia coli and Klebsiella pneumoniae including extended spectrum β-lactamase producing strains

Abstract

In vitro activity of ceftiofur, a cephalosporin used in veterinary practice was compared using ceftriaxone-resistant (producing extended spectrum β-lactamase (ESBL)) and -susceptible clinical isolates of Esherichia coli and Klebsiella pneumoniae. The ceftriaxone-susceptible isolates exhibited a lower range of ceftiofur MICs (MIC 50, 0.5 mg/l, MIC 90 1.0 mg/l). Those isolates known to produce an ESBL were also resistant to ceftiofur (MIC 50, ≥ 32 mg/l). The latter isolates were also less susceptible to other comparator drugs (cefquinome, gentamicin and trimethoprim/sulphamethoxazole) in contrast to the ceftriaxone-susceptible strains. The clinical isolates showed high correlation between ceftriaxone and ceftiofur MICs ( y=2.6+0.89 x, r=0.95). Using the current ceftiofur susceptible breakpoint (≤2 mg/l) used for veterinary practice (respiratory tract pathogens), the ESBL-producing strains of E. coli and K. pneumoniae could be accurately separated from susceptible strains. This ceftiofur breakpoint MIC corresponds to the National Committee for Clinical Laboratory Standards ESBL screening concentration for ceftriaxone set at ≤1 mg/l=negative for ESBL production. Ceftiofur was also observed to be very active in vitro against ampicillin-resistant, non-ESBL producing enteric isolates. This new cephem appears to be very potent against the tested Enterobacteriaceae and of potential wide clinical veterinary utility.