Role of the bsr gene in the Intracellular Survival of Bordetella bronchiseptica

Hira Hasan, a student from Louisiana State University, worked with Monica Cartelle-Gestal in the lab of Dr. Eric Harvell to study the intracellular survival of Bordetella bacteria.

Abstract:  Bordetella pertussis and B. parapertussis are Gram-negative bacteria that cause a respiratory infection, known as whooping cough, in humans. Another member of the Bordetella species, B. bronchiseptica (BB), primarily infects mice, dogs, and horses.  The wild type strain of BB, RB50, contains a gene (bsr) encoding a putative sigma factor that is up-regulated when BB is exposed to blood. To test the role of this gene in pathogen-host interactions, a knock-out mutant called RB50Δbsr was made in our lab. Preliminary results showed that RB50Δbsr survives longer within macrophages than RB50. The mutant also confers sterilizing immunity against further BB, B. pertussis, and B. parapertussis infection in mice, which are excellent models for human infection. The aim of this study was to determine if there is a difference between how RB50 and RB50Δbsr are internalized by macrophages, specifically whether the latter survives longer intracellularly by inhibiting lysosome formation. Confocal microscopy and a lysotracker assay were used to determine the location of bacteria within macrophages, while electron microscopy and several internalization assays were conducted to quantify live bacteria within macrophages overtime. We found that there are higher levels of intracellular RB50Δbsr than RB50 over a 24-hour period, RB50Δbsr does not enter lysosomes readily, and RB50Δbsr infection results in less macrophage death. Based on the results of this study, bsr plays a vital role in macrophage response to BB infection. Since macrophages are involved in activating several other immune system components, manipulating bsr leads to an overall change in the persistence of Bordetella infections.

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