Francisella tularensis, which is the agent of tularemia, is an intracellular disease-causing organism as seen via microscopy using the microscopes such as darkfield compound microscope, but not much is known regarding the compartment where it dwells in human macrophages. The science researchers have investigated the interaction of a current virulent clinical isolate of Francisella tularensis subspecies tularensis and the living vaccine strain with the human macrophages by means of immunoelectron and the confocal immunofluorescence microscopy. The science researchers evaluated the maturation of the Francisella tularensis phagosome by means of studying its acquirement of the lysosome-associated membrane glycoproteins or LAMPs CD63 and LAMP1 as well as the acid hydrolase cathepsin D.
In two to four hours subsequent to contamination, vacuoles having live Francisella tularensis cells obtained plenty staining for LAMPs but not much or zero staining for cathepsin D as observed through microscopy using some microscopes such as darkfield compound microscope. Nevertheless, after four hours, the colocalization of the LAMPs with the live Francisella tularensis organisms decreased gradually. In the contrary, vacuoles having formalin-destroyed bacteria displayed extreme staining for all of these late endosomal/lysosomal indicators at all time points examined from one hour to sixteen hours. The science researchers investigated the acidity of the vacuoles in three to four hours after contamination by the quantitative immunogold staining and by the fluorescence staining for lysosomotropic agents by means of microscopy using the microscopes.
While phagosomes that contained destroyed bacteria stained strongly for these agents, signifying a marked acidification of the phagosomes, phagosomes having live Francisella tularensis did not concentrate these indicators and hence were not considerably acidified as observed through microscopy using the microscopes such as darkfield compound microscope. An ultrastructural examination of the Francisella tularensis compartment exposed that during the first four hours after uptake, most of the Francisella tularensis bacteria dwell inside the phagosomes with certain membranes as seen via microscopy using the microscopes like the darkfield compound microscope. In various instances, these coated phagosomal membranes seemed to bud, vesiculate and disintegrate as examined by means of microscopy using the microscopes such as darkfield compound microscope.
By eight hours after contamination, most of the live Francisella tularensis bacteria are deficient in any ultrastructurally perceptible membrane segregating them from the host cell cytoplasm. These outcomes signify that Francisella tularensis primarily enters a nonacidified phagosome with LAMPs but with no cathepsin D and that the phagosomal membrane consequently turns morphologically disturbed, permitting the bacteria to acquire direct entry to the macrophagic cytoplasm. The ability of Francisella tularensis to change the maturation of its phagosome and to join the cytoplasm is possibly a vital element of its ability to parasitize macrophages and has main implications for vaccine formation.

Francisella tularensis is a non-motile, non-sporulating, gram-negative coccobacillus that triggers a zoonotic illness in tiny animals like rodents, rabbits and beavers as examined by means of microscopy using the microscopes such as darkfield compound microscope. Humans obtain tularemia by means of handling contaminated animals or by the bite of a blood-sucking insect. The contagion of Francisella tularensis is noteworthy, a subcutaneous injection of mice with as few as half to four organisms of the virulent Schu strain ends-up in a deadly contamination in fifty percent of the animals. In addition to initiating severe and possibly life-threatening natural contaminations in humans and animals, Francisella tularensis is also believed to be a potential agent of bioterrorism. There are two chief biogroups of Francisella tularensis, specifically Francisella tularensis subspecies tularensis or the type A, and Francisella tularensis subspecies holarctica or the type B. Type A is discovered only in North America and is greatly virulent. Type B is discovered in North America and in Europe and has a lesser level of virulence. A moderately assuaged live vaccine strain was grown from type B and has been utilized as a vaccine with certain success. Nevertheless, the safety of this vaccine for immunocompromised people and kids are not known, and it is not presently approved for use in humans in America. The progress of novel strategies for treating or preventing the tularemia is delayed by the limited information of the pathogenic mechanisms of Francisella tularensis.