FIG. 6.

Effect of ammonium chloride (A) and acidic shock (B) on the intracellular survival of Brucella in human monocytes. Freshly isolated PBM were challenged with nonopsonized B. suis for 20 min and chased for 1 to 36 h. Viable bacteria reisolated from osmotically lysed monocytes were determined by count of CFU. Results are expressed as means ± standard deviations for duplicate samples from one out of three experiments with monocytes from different donors which gave comparable results. (A) Compared is the survival of B. suis in the absence (no) or presence of 30 mM ammonium chloride added either immediately (0 h) at the onset of chase or up to 9 h later. (B) Compared is the survival of B. suis kept at either neutral or acidic pH for 4 h prior to infection. (C) Electron micrograph of a Brucella-infected monocyte chased for 8 h in the continuous presence of ammonium chloride. All Brucella-bearing phagosomes are spacious, and the internalized bacteria are degraded. Bar, 1 μm.