FIG 7.

Infection of C56BL/6 mice with WT S. Javiana results in a higher bacterial load in the liver, but not in the spleen, ileum, or cecum, compared to infection with a ΔcdtB strain. Eight-week-old female C56BL/6 mice were orally inoculated with 1 × 10⁹ CFU S. Javiana wild-type or ΔcdtB strain (five mice in each group). At 48 hpi, the mice were euthanized, and tissues were harvested for bacteriologic and histological examination. (A) S. Javiana cells were enumerated from the liver, spleen, ileum, and cecum. The average bacterial load was calculated for each tissue. The limit of detection (LOD) for the average bacterial load for all tissues was 5 CFU. Differences in S. Javiana recovered from each tissue were compared using the nonparametric Kruskal-Wallis test. (B and C) Sections of the distal ileum, cecum, and proximal colon were fixed in buffered formaldehyde, embedded in paraffin, sectioned, and stained with hematoxylin and eosin. The levels of polymorphonuclear leukocytes (PMN) in the cecum (Ce) and proximal colon (Co) were scored on a scale of 0 to 4 (0 representing no PMNs and 4 representing large numbers of PMNs); cryptitis was assessed using the same scale. The degree of edema was scored from 0 (no edema) to 3 (severe edema). (C) The pathology score for typhlocolitis represents the sum of the scores (maximum score is 15) in panel B. Statistical differences in the counts of mice in each category of pathology score were assessed using the nonparametric Kruskal-Wallis test. Each symbol represents the value for an individual mouse. Black bars represent the median bacterial load (A) or median pathology scores (B and C) for mice infected with each S. Javiana strain. Values that are significantly different (P < 0.05) are indicated by a bar and asterisk. Only statistical associations with P < 0.05 are shown.