IAI Accepts, published online ahead of print on 26 October 2009

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Infect. Immun. doi:10.1128/IAI.00668-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Division of Salmonella-Containing Vacuole and Depletion of Acidic Lysosomes in Salmonella-Infected Host Cells: A Novel Strategy of Salmonella to Avoid Lysosomes.

Sandeepa M. Eswarappa, Vidya Devi Negi, Sangeeta Chakraborty, B. K. Chandrasekhar Sagar, and Dipshikha Chakravortty^*

Centre for Infectious Disease Research and Biosafety Laboratories, Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore - 560012, Karnataka, INDIA; Electron Microscopy Laboratory, Department of Neuropathology, National Institute of Mental Health and Neuro Sciences, Bangalore - 560029, Karnataka, INDIA

^* To whom correspondence should be addressed. Email: dipa{at}mcbl.iisc.ernet.in.

Salmonella has evolved several strategies to counteract intracellular microbicidal agents like reactive oxygen and nitrogen species. However, it is not yet clear how Salmonella escapes lysosomal degradation. Some studies have demonstrated that Salmonella can inhibit the phagolysosomal fusion, whereas some reports have shown that Salmonella-containing vacuole (SCV) fuses/interacts with lysosomes. Here, we have addressed this issue from a different perspective by investigating if the infected host cell has sufficient quantity of lysosomes to target Salmonella. Our results suggest that SCVs divide along with Salmonella resulting in single bacterium per SCV. As a consequence, the SCV load per cell increases with the division of Salmonella inside the host cell. This demands more investment from the host cell to counteract Salmonella. Interestingly, we observed that Salmonella infection decreases the amount of acidic lysosomes inside the host cell both in vitro and in vivo. These events potentially result in a condition where an infected cell is left with insufficient acidic lysosomes to target the increasing number of SCVs, which favors the survival and proliferation of Salmonella inside the host cell.