Molecular characterization of OXA-48 carbapenemase-producing Klebsiella pneumoniae strains after a carbapenem resistance increase in Catalonia.

Introduction: To characterize OXA-48 carbapenemase-producing Klebsiella pneumoniae strains isolated after an increase in carbapenem resistance in Catalonia.

Methodology: K. pneumoniae identification, antimicrobial susceptibility studies, the Modified Hodge Test method, amplification of antimicrobial resistance genes (against β-lactamases, quinolones and aminoglycosides), molecular typing (by PFGE and MLST), conjugation assays, plasmid characterization (PBRT-PCR and Southern blot), a description of mobile genetic elements and statistical analysis were done.

Results: OXA-48 was the only carbapenemase detected, with a prevalence of 1.9%. The bla gene was located in an IncL conjugative plasmid of 62kb and integrated into the transposons Tn1999.2 (91.7%) or Tn1999.1. Five PFGE profiles (A to E) were found, which exactly matched the MLST: ST101, ST17, ST1233, ST14 and ST405, respectively. ST1233 is described here for the first time. K. pneumoniae OXA-48-producing strains were also CTX-M-15 carriers, some producing OXA-1 and TEM-1 penicillinases. The acquired qnrB66 and qnrB1 and aac(3')-IIa, aac(6')-Ib genes were also identified.

Conclusion: The K. pneumoniae ST405 clone has played an important role in the growing prevalence of OXA-48 in Catalonia. All clones described preserved the bla genetic environment and mobile genetic elements (Tn1999). Notably, the three strains with minor sequence types in this study are not multiresistant strains. These strains are expanding in elderly patients (average age of 76 years) with serious underlying diseases, mainly women (61.2%).