Morphological study of Pseudomonas aeruginosa virulent and avirulent strains and their fate in the infected peritoneal macrophages

Abstract

Pseudomonas aeruginosa is an opportunistic pathogen which often infects debilitated patients, sometimes with a fatal outcome. Although numerous in vestigations have attempted to determine the relationships between the elaboration of particular virulence-associated factors and Pseudomonas infection, the role that these factors play in vivo is not clear, nor is there general agreement on the mechanism of pathogenesis of this organism, on its interaction with the host defense mechanism.
In the present study, P. aeruginosa. virulent (NC-5) and avirulent (TE-14) strains for mouse were studied on their ultrastructure, on their relation to mouse peritoneal exudate cells (PEC) in vivo and in vitro from the view point of host-parasite relationships. And following results were obtained.
1. The organ ism of both strains had typical Gram-negative structure. Their size was 0.3-0.7×1.4-3.5 μm. TE-14 was motile by single pollar flagellum but NC-5 was no n flagellated. Capsule, slime layer or pili, which correlate with pathogenicity of bacter i a, were found in neither strains of bacteria.
2. Small pits, about 12 nm in outer diameter, were formed on the outer membrane when both organisms were treated with trypsin. Furthermore, spherical particles of 4.0-4.5 nm in diameter were tetragonally arranged with regular periodicity of 10 nm on peptidoglycan layer. These structures were found on both strains of bacteria and were th o ught to be fundamental structure for P. aeruginosa.
3. TE-14 was phagocyted by PEC and was digested in the phagosome but NC-5 was resistant to both actions of PEC. This difference between two strains was also shown by m orphological studies with light and electron microscopy, and by assays for bacterial v i a bility and for acid phosphatase activity. These results suggested the presence of anti-phag o cytic component in the cell wall of virulent strain.
4. NC-5, a virulent strain for mouse, lost the cell wall rigidity when it was treated with antibody and gentamicin. This NC-5 was easily phagocyted by PEA similar to in t act TE-14 and was digested in the phagosome. These results elucidate the mechanism of combination effect with antibody and antibiotics.
From these results, follwings are conclud ed. Difference for resistance to phagocytosis and to digestion by peritoneal cells was shown between P. aeruginosa. virulent and avirulent strains. It was suggested that this difference due to the anti phagocytic structural component, present in the cell wall of virulent strain. This component was affected its rigidity with antibody and antibiotics. Pits and paricle structures which were observed on the cell wall by electron microscopy after trypsinization were thought to be fundamental structures for P. aeruginosa.