Background/purpose: The emergence of Klebsiella pneumoniae carbapenemase (KPC)-producing strains is a challenge for clinicians. The characteristics and virulence of variants of KPC-producing K. pneumoniae isolates were evaluated. Methods: Five clinical isolatesdthree KPC subtypes from Taiwan (KPC2-TW, KPC3-TW, and KPC17-TW) and two clinical strains from the United States (US; KPC2-US, KPC3-US)dwere included. Virulent traits and capsular serotypes were analyzed by Polymerase Chain Reaction

more »

... Serum killing, neutrophil phagocytosis, and mice lethargy studies were performed to evaluate virulence. Results: Multilocus sequence typing (MLST) demonstrated that KPC2-TW and KPC17-TW belonged to sequence type (ST)11, and KPC2-US, KPC3-US, and KPC3-TW to ST258. KPC3-TW expressed capsular serotype K1, whereas the others were non-K1/K2/K5 isolates. MLST analysis indicated that ST11 strains were serum resistant, whereas ST258 isolates were serum sensitive. Journal of Microbiology, Immunology and Infection (2016) 49, 83e90 ST11 isolates exhibited significantly higher 15-minute phagocytic rates than ST258 isolates (70.28 AE 16.68% vs. 34.88 AE 10.52%, p < 0.001). The capsular serotype K1 strain was more resistant to neutrophil phagocytosis than non-K1/K2/K5 isolates (27.1 AE 10.23% vs. 54.46 AE 20.94%, p Z 0.050). All KPC-producing strain variants from Taiwan and the US demonstrated less virulence in a mouse lethality study, where the LD 50 ranged from approximately 10 6 colony-forming units (CFU) to >10 7 CFU. Immunological responses were not significantly correlated with KPC subtype; however, responses were associated with MLST and capsular serotype. Conclusion: Production of KPC itself was not associated with increased virulence despite different variants of KPC. The ST11 KPC-producing strain was resistant to serum killing, whereas capsular ss K1 was associated with resistance to neutrophil phagocytosis.