Fig 1.
Phagocytosis of neutrophils against HvKP-K1, HvKP-K2 and cKP.
The rate of phagocytosis against cKP (15 isolates) was higher than that against HvKP-K1 (16 isolates) or HvKP-K2 (14 isolates) at 10, 30, 60 min. The mean ± standard deviation (S.D.) of each group at each time point was calculated respectively. Statistics was performed using one-way analysis of variance for each time point. Differences between groups were assessed by t test. At 10, 30, 60 min, HvKP-K1 vs. cKP or HvKP-K2 vs. cKP: p < 0.05.
Fig 2.
Survival of cKP, HvKP-K1 and HvKP-K2 within human neutrophils.
The survival index was calculated with the equation described in the method. The survival index of cKP (15 isolates) was lower than that of HvKP-K1 (16 isolates) or HvKP-K2 (14 isolates). Each strain was repeated twice and averaged. Then the mean ± standard deviation (S.D.) of each group was calculated. Statistics was performed using one-way analysis of variance. Differences between groups were assessed by t test. HvKP-K1 vs. cKP or HvKP-K2 vs. cKP: p < 0.001.
Fig 3.
Examination under transmission electron microscopy.
Phagocytosed cKP (3 isolates, A) and HvKP-K1 (3 isolates, C) by neutrophils at 30 min (×3K); lysed cKP lack of intact cell wall (3 isolates, B) and binary fission multiplying HvKP-K1 (3 isolates, D) at 60min (×6K). Bacteria were indicated by black arrows.
Fig 4.
NETs under scanning electron microscopy.
NETs induced by PMA (A and B), cKP (3 isolates, C and D), and HvKP-K1 (3 isolates, E and F). More cKP (C) than HvKP-K1 (E) were trapped in NETs by magnification of 5K. The pores (indicated by white arrows) on the surface of cKP, but not on the surface of HvKP-K1 were observed by magnification of 20K (D and F). Bacteria were indicated by black arrows.
Fig 5.
Immunofluorescence staining under confocal microscopy.
Neutrophils challenged by cKP (9 isolates, A-D) and HvKP-K1 (9 isolates, E-H) were stained for DNA (DAPI, blue, A and E), myeloperoxidase (MPO, red, B and F) and citrullinated histone H3 (cit-H3, green, C and G). The merged images of cKP (D) and HvKP-K1 (H) illustrated the characteristic neutrophil extracellular traps. Original magnification 40×.