CTX-M-15 extended-spectrum β-lactamase from Nigerian Klebsiella pneumoniae

Abstract

Objectives: In this study, extended-spectrum β-lactamases (ESBLs) were characterized from 30 selected multidrug-resistant Klebsiella pneumoniae strains isolated from patients with community-acquired urinary tract infections from Southwest Nigeria. Methods: The β-lactamases were phenotypically characterized using isoelectric focusing, genotypically characterized using PCR assays and hybridization of the PCR products. Two of the bla_CTX-M genes were completely sequenced. The location of the CTX-M-type genes was determined using transformation, DNA–DNA hybridization, PCR assays and hybridization of the PCR products from the Escherichia coli transformants. Results: All 30 isolates produced at least one β-lactamase. Seventeen of the isolates were resistant to cefotaxime, and had ≥100-fold reduction in susceptibility with cefotaxime plus clavulanic acid (4 mg/L), indicating the presence of an ESBL. The 17 isolates were shown to have bla_CTX-M genes that were associated with large plasmids (≥58 kb), which also carried a tetracycline resistance gene, tet(A), and various aminoglycoside resistance genes. Two CTX-M-type genes were sequenced and had amino acid sequences indistinguishable from previously sequenced CTX-M-15 β-lactamases. The ISEcp1 element was located upstream of bla_CTX-M-15 in the same position as previously described. In addition, 23 of the isolates produced TEM β-lactamases, 27 produced SHV β-lactamases and four produced AmpC β-lactamases. Conclusions: Thirty K. pneumoniae produced multiple β-lactamases, with 57% producing CTX-M enzymes. This is the first characterization of CTX-M-15-positive K. pneumoniae in Western Africa.