Table 1.
Distribution of serum-sensitive and serum-resistant serotypes of K. pneumoniae selected for this study.
Figure 1.
The effect of serum dilution on the serum killing of K. pneumoniae serotypes K1 and K6.
A high concentration of serum inhibited the growth of K6 but not K1. Each experiment was repeated in triplicate. The bacteria counts are expressed by cell forming unit (CFU).
Figure 2.
The rate at which neutrophils from 11 healthy volunteers killed serotypes K1 and K6 K. pneumoniae.
The percentage of killing is expressed as the mean ± SD and calculated as the total number of bacteria killed divided by the number of viable bacteria in the initial inoculum. K1 vs. K6: p<0.01 (n = 3 for each).
Figure 3.
Electron microscopic examination of phagocytosed serotypes K1 and K6 K. pneumoniae.
Vacuolated bacteria are evident. The cell wall structure of serotype K1 appears intact, and cell division patterns are visible despite digestion by neutrophils (A & C). In contrast, lysis and the loss of cell wall structure of serotype K6 is seen in the vacuoles of neutrophils (B & D). (Bar = 1 µm, cells magnified ×6K; bar = 200 nm, cells magnified ×20K). Bacteria are pointed by arrow.
Figure 4.
Survival rate of BALB/c mice (n = 12 per group) following intraperitoneal injection of neutrophils containing phagocytosed serotypes K1 and K6 K. pneumoniae.
The number of viable intracellular bacteria were 4×103 and 5×105 for serotypes K1 and K6. Survival was observed for 10 days. Each experiment was repeated twice. (A) Human neutrophils. (B) BALB/c neutrophils. (p<0.001, for the serotype K1 group vs. the K6 and control groups in human and mouse experiments.)
Figure 5.
Gross abscess appearance in mice injected with neutrophils containing phagocytosed serotype K1 K. pneumoniae.
A: Neck. B: Surgical removal of the abscess site. C: Abdomen. D: Abscess formation in liver and subcutaneous areas. E: (1) Morphological features of injected serotype K1 K. pneumoniae and (2) culture of pus discharge from the abscess site. F: Detection of the serotype K1 specific magA gene and intrinsic blaSHV gene from (1) the parental strain and (2) bacteria isolated from the abscess site. G: PFGE molecular typing of (1) the parental strain and (2) bacteria isolated from the abscess site. Sites of abscess formation are indicated by red arrows.
Table 2.
Mortality and abscess formation after intraperitoneal (IP) injection of neutrophil-phagocytosed serotype K1 and K6 K. pneumoniae.
Figure 6.
Pathologic features of abscesses due to serotypes K1 and K6 K. pneumoniae in different mouse tissues.
(A). Necrosis can be seen in the liver and at metastatic infection sites in mice injected with K1 K. pneumoniae. No inflammation was seen in the liver of mice injected with serotype K6. (B). Inflammation was not found in the lungs, spleen, or kidneys of mice injected with serotypes K1 and K6.