Outbreak of multi-resistant Klebsiella oxytoca involving strains with extended-spectrum β-lactamases and strains with extended-spectrum activity of the chromosomal β-lactamase

Objectives: This study was conducted to analyse broad-spectrum cephalosporin-resistant Klebsiella oxytoca strains. Methods: The 57 isolates studied were recovered from clinical specimens (n = 23) or from rectal swabs (n = 34) during a 26-month period. Antibiotic susceptibility patterns were determined using standard agar diffusion and dilution methods including the synergy test between extended-spectrum cephalosporins and clavulanic acid. ERIC-2 PCR and pulsed-field gel electrophoresis (PFGE) methods were used to study the clonal relatedness of the strains. Plasmid-mediated and chromosomal β-lactamases were characterized by mating and specific bla gene amplification and sequencing. Results: Four different antibiotic resistance patterns were identified whereas ERIC-2 PCR and PFGE revealed six main profiles. Extended-spectrum β-lactamases (ESBLs) were found in 32 strains: TEM-7 (n = 26), TEM-129 (n = 1), TEM-3 (n = 4), SHV-2 (n = 1). The new TEM-type β-lactamase, TEM-129, differed from TEM-7 by one mutation (Glu-104 → Lys). All TEM-7 or TEM-129 producers were genetically related. Twenty-five other strains with identical ERIC-2 PCR and PFGE profiles harboured a bla OXY-2 gene different from the reference gene: 24 strains displayed one substitution (Ala-237 Ser) in the KTG motif and one strain, highly resistant to ceftazidime, showed an additional substitution (Pro-167 → Ser). Conclusions: The study demonstrated that the majority of strains (n = 52) harbouring the OXY-2-type β-lactamase corresponded to two clones. The first clone (n = 27) corresponded to ESBL-producing strains. The second clone (n = 25) displayed extended-spectrum activity of the chromosomal β-lactamase.