Shift in the Dominant Sequence Type of Carbapenem-Resistant Klebsiella pneumoniae Bloodstream Infection from ST11 to ST15 at a Medical Center in Northeast China, 2015-2020

Objective: To investigate the clinical characteristics and molecular epidemiology of carbapenem-resistant Klebsiella pneumoniae (CRKP) bloodstream infection at a medical center in northeast China, especially after coronavirus disease (COVID-19) pandemic. Methods: Fifty-one patients were diagnosed with CRKP bloodstream infection between January 2015 and December 2020, among which 42 isolates were available for further study. Species identification and antibiotic susceptibilities were tested with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and VITEK 2 systems. Carbapenemase genes, virulence genes and MLST genes were detected by polymerase chain reaction. Moreover, the string test and serum killing assay were performed to evaluate the virulence of the CRKP isolates. Results: During the six-year period, the detection rate of CRKP in bloodstream infection showed an increasing trend, with the intensive care unit, hematology and respiratory medicine wards mainly affected. Molecular epidemiology analyses showed that KPC-2 was the dominant carbapenemase gene. In addition, the dominant sequence type (ST) of CRKP shifted from ST11 to ST15 strains, which were all sensitive to amikacin in contrast to the ST11 stains. Furthermore, ST15 CRKP strains were positive for the KfuB virulence gene and more resistant to serum killing compared to the ST11 CRKP strains. Nonetheless, the mortality rate of patients infected with ST11 and ST15 CRKP did not show any significant differences. Conclusion: A shift in the dominant sequence type of CRKP bloodstream infections from ST11 to ST15 was observed during the years 2015-2020. Compared to ST11, the ST15 CRKP strains showed amikacin sensitivity, positivity for KfuB gene, and serum resistance, which may indicate stronger virulence.