After excretion by B cells, <i>Salmonella</i> is capable of infecting secondary host cells.

<p>(A) Left panel: the effect of antibiotics on the growth of lux-<i>Salmonella</i> in Ramos B cells. Right panel: the same FACS analysis with primary B cells as in 2C was performed in presence of either Gentamicin or Tetracycline to discriminate between host and bacteria mediated excretion. (B) Quantification of <i>Salmonella</i> secretion from B cells. Primary B cells were incubated with live uncoated GFP-<i>Salmonella</i> in presence of either Gentamicin or Tetracycline to discriminate between host versus bacterial-mediated excretion. Cells were stained with antibodies against LPS, fixed and analyzed using FACS. Increase in cell surface LPS levels is similar in the presence of Gentamicin and Tetracycline, indicating that viable <i>Salmonella</i> are not required for excretion. (C) Primary B cells having phagocytosed anti-IgM coated GFP-<i>Salmonella</i> on a monolayer of 3T3-CD40L fibroblasts were imaged using widefield fluorescence microscopy for the times indicated. Imaging conditions are similar as in 2A. GFP-<i>Salmonella</i> is excreted from a primary B cell (white arrowhead), followed by infection of the 3T3-CD40L monolayer (outline of infected cell marked by a dashed line). Inset shows zoom-in on primary B cell excreting GFP-<i>Salmonella</i>. Images are frames from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0050667#pone.0050667.s007" target="_blank">Video S6</a>.