Klebsiella pneumoniae: Development of Carbapenem Resistance due to Acquisition of blaNDM-1 During Antimicrobial Therapy in Twin Infants with Pneumonia

Objectives: To identify the mechanism of in vivo development of carbapenem resistance in Klebsiella pneumoniae. Methods: Seven sequential isolates of K. pneumoniae were obtained from twin infants with pneumonia. Antimicrobial susceptibility testing was performed by agar dilution method. Carbapenemases including KPC and M beta L were initially screened using phenotypic methods, and carbapenemase-encoding genes were identified by polymerase chain reaction and amplicon sequencing. Plasmids of all clinical isolates and the conjugants of resistant isolates were estimated by 51 pulsed-field gel electrophoresis (PFGE). Molecular typing were conducted by PFGE of Xbal-digested genomic DNA and multilocus sequence typing. Results: For old brother, the first and third isolates were susceptible to meropenem, whereas the second and fourth isolates were resistant (MICs 16 mg/L). The first and second isolates from the young brother were susceptible to meropenem whereas the third isolate was resistant. All the resistant isolates produced NDM-1 metallo-beta-actamase. PFGE of Xbal-digested DNA revealed almost identical patterns with similarity indices of above 92% for all the seven isolates. All the isolates had the same sequence type named sequence type 37 (5T37). Conclusion: To our knowledge, this is the first documented case of development of carbapenem resistance in vivo mediated by NDM-1 metallo-beta-lactamase in K. pneumoniae during treatment of pneumonia with meropenem.