Figure 5

The capsule protects Cc5 against serum and polymyxin B killing and phagocytosis.

(a) Total bacterial CFU present after incubation with 10% heat inactivated human serum (HIHS) or 10% normal human serum (NHS) for 1 hour at 37 °C. Mean values from 3 different experiments and standard deviations are represented (***p ≤ 0.001 compared to wt). (b) Phagocytosis of Cc5 bacteria by J774A.1 macrophages. J774A.1 macrophages were incubated with eFluor^®-stained bacteria and subsequently analyzed by FACS. Cytochalasin D (CytD) pretreatment of macrophages was performed to inhibit phagocytosis. Mean values from 3 different experiments and standard deviations are represented (***p ≤ 0.001, **p ≤ 0.01 compared to wt). ni = non-infected macrophages. (c) Role of capsular polysaccharide on polymyxin B resistance. MIC of Polymyxin B for Cc5 wt, Y1C12, waaL (rough LOS), and Δwza (wzz⁺) (non-capsulated) bacteria. Data were combined from 3 independent experiments where measured MIC were identical. (d) Effect of opsonization on serum killing. Total bacterial CFU of wt Cc5 present after incubation with HIHS or NHS and NHS in the presence of heat inactivated normal rabbit serum (NHS + NRS) or heat inactivated anti-Cc5 Y1C12–adsorbed rabbit serum (NHS + Y-ads). Mean values from 3 different experiments and standard deviations are represented (**p ≤ 0.01 compared to NHS).