Intracellular bacterial pathogens and their survival strategies

An intracellular life cycle can have several advantages for bacterial pathogens. Nutritionally, the bacteria absorb food from their host cell (some such as Rickettsia are even energy parasites - they directly absorb host cell ATP). Secondly, intracellular bacteria are shielded from the immune system and especially protected from humoral immunity. Disease symptoms are often the result of the destruction of the infected host cells (e.g. the intestinal lining in Shigellosis). Cell-mediated immunity is necessary to fight the infection, but this often causes further tissue damage due to inflammation. The symptoms of intracellular infections often are due to host immune responses (e.g. TB and LGV lead to granulomas and inflammatory swelling). Diagnostically and treatment-wise, intracellular pathogens also present unique challenges. Some cannot be cultured in the lab without host cells (e.g. Rickettsia).

The major intracellular pathogens and their strategies are:

Pathogen Host cell Survival strategy
Bartonella RBCs, endothelial cells Inhibit phagolysosome fusion
Brucella spp. Monocytes/macrophages Inhibit phagolysosome fusion
Chlamydia Nonciliated epithelium Inhibit phagolysosome fusion
Coxiella Macrophages Survive in lysosome 
Ehrlichia spp. White blood cells Inhibit phagolysosome fusion
E. coli (EIEC, EHEC) Intestinal epithelium Enter cytoplasm
Francisella tularensis Monocytes/macrophages Enter cytoplasm
Listeria monocytogenes Macrophages, epithelial cells Enter cytoplasm
Legionella pneumophila Alveolar macrophages/monocytes Inhibit phagolysosome fusion
Mycobacterium tuberculosis Alveolar macrophages Inhibit phagolysosome fusion
Mycobacterium leprae Macrophages, monocytes, Schwann cells, endothelial cells Survive in lysosome 
Neisseria gonorrhoeae Nonciliated epithelial cells, phagocytes Inhibit phagolysosome fusion
Neisseria meningitidis Nonciliated epithelium, phagocytes Survive in lysosome 
Orientia tsutsugamushi Vascular endothelium Enter cytoplasm
Rickettsia Vascular endothelial cells Enter cytoplasm
Salmonella spp. Intestinal M-cells Survive in lysosome 
Salmonella typhi M-cells, macrophages Survive in lysosome 
Shigella spp. M-cells of colon; macrophages Enter cytoplasm


  2. CEL8/html/leprosypathogenINtlJDerm1999.pdf