Characterization of ceftriaxone-resistant enterobacteriaceae: A multicentre study in 26 french hospitals

During a multicentre study performed in 26 French hospitals, 287 (3·2%) of 9038 Enterobacteriaceac isolated, mainly Enterobacter spp., Serratia spp., Citrobacter spp. and Kiebsiella spp. were classified as ceftriaxone resistant on the basis of an MIC >4 mg/L or the presence of an extended-spectrum β-lactamase. Extended-spectrum β-lactamase was present mainly in Kiebsiella pneumoniae (65 strains, 10·2%) and very rarely in Escherichia coli, Proteus mirabilis, Klebsiella oxytoca, Citrobacter spp. and Enterobacter spp. The extended-spectrum β-lacta mases conferred low-level resistance to ceftriaxone in nearly 60% of the strains harbouring them, emphasizing the need for routine testing for the presence of these enzymes. Among transconjugants three types of extended-spectrum β-lactamase were identified. Those resembling TEM-3 were the most common, but TEM-21, and SHV-4 were also found. Clavulanate and to a lesser extent sulbactam inhibited all the extended-spectrum β-lactamases encountered in this study.