Clinical characteristics in blood stream infections caused by Klebsiella pneumoniae, Klebsiella variicola, and Klebsiella quasipneumoniae: a comparative study, Japan, 2014-2017

Background Klebsiella variicola and K. quasipneumoniae are new species distinguishable from K. pneumoniae but they are often misidentified as K. pneumoniae in clinical settings. Several reports have demonstrated the possibility that the virulence factors and clinical features differ among these three phylogroups. In this study, we aimed to clarify whether there were differences in clinical and bacterial features between the three phylogroups isolated from patients with bloodstream infections (BSIs) in Japan. Methods Isolates from all patients with BSIs caused by K. pneumoniae admitted to two hospitals between 2014 and 2017 (n = 119) were included in the study. Bacterial species were identified via sequence analysis, and their virulence factors and serotypes were analyzed via multiplex PCR results. Clinical data were retrieved from medical records. Results Of the 119 isolates, 21 (17.7%) were identified as K. variicola and 11 (9.2%) as K. quasipneumoniae; K1 serotype was found in 16 (13.4%), and K2 serotype in 13 (10.9%). Significant differences in the prevalence of rmpA, iutA, ybtS, entB and kfu (p < 0.001), and allS genes (p < 0.05) were found between the three phylogroups. However, there were no significant differences in clinical features, including the 30-day mortality rate, between the three organisms, although K. variicola was more frequently detected in patients over 80 years old compared with other Klebsiella species (p < 0.005), and K. quasipneumoniae more frequently occurred in patients with malignancy (p < 0.05). Conclusions Our findings demonstrated the differences in bacterial pathogenicity and clinical features among these three phylogroups. Further epidemiological studies into BSI caused by Klebsiella species are warranted.