Induction of brain lesions experimentally by inoculation of Staphylococcus aureus subcutaneously in rabbits (A histological study)

Six aduit rabbits of both sexes were used tostudy the effect of Staphylococcus aureus on lhebrain tissue. Animals were classified into two groups. Group(A) was the control and Group(B) was the treated. Group (A) was inoculated with 0.8m1 saline solution subcutaneously, and group (B) was inoculaied subcutaneously with 0.8m1 suspension of ,S/aph.aureus .The inculation process was tepeated again with group (B) after 15 day. After (15) days from the second inoculation, the all animals of both groups were sacrified. A brain specimens from the frontel, parietal and temporal lobes of both groups were taken, processed for histological tech-nique, embedded in the paraffin wax, sectioned at (5) pm thickness and stained by the haematoxylin & eosin lor examination by the light microscopy. The brain tissues of group B, demonstrated the histopathological changes of the whole sites of the brain lobes, included, focal necrosis of the nerve cells, dernyelination of the nerve fibers and gliosis. This effect may reflect the efficacy of the bacteria or its toxin or many both on the brain tissues.


Literature Review
Ryan (5) revealed that the patient may develop a brain abscess , fluminant meningitis or infection at the other body sites, excessive bleeding and shock can derelop lrom the bacterial invasion .
Bacteria such as Staph.dureus may be introduced into the cerebral substance through the pentrating injury direct spread from sinuses or the middle ear or through embolism to brain tissue (6).
Initial infection leads to local suppuration followed by loculation of pus within the surrounding wall of gliosis which is chronic abscess may from a tough capsule,multiple abscen occur particulary with metastatic spread (7) .Betty (8)demonstrated that bacterial meningitis is usually secondary to bacteramic illness although the infection may result from direct spread from an adjacent focus.

Materials and Methods
Bacterial suspension was prepared for inoculation the experimental rabbits by obtaining the colonies of Staph. aureus fi'om the blood agar and placed in the nutrient broth. 0.8m1 of the bacterial suspension has been aspirated and inoculated subcutaneously in the experimental rabbit (9). Six adult rabbits of both sexes,r/ere prepared ,weighting 500-750gm, food and water were available .The rabbits were classified into two groups as indicated in the The animals of the group B were re inoculated with the bacterial suspension after 15 days . All animals were survived for (30)day post 1't inoculation. All animals were deeply ,inhalated with ether and decapatated immediately Brain specimens from the frontal , parietal and temporal lobes of both groups were taken after breaking down the skull gently. The specimens were rinsed with running water , then placed in 10% formalin for 48 hours and processed through graded ethyl alcohol series 70,90 and absolute , xylene .Then infillterated in paraffine wax, blocked and prepared for sectioning .Sections of (5pm) thickness were prepared , stained by H&E (10), and examined by light microscope .

Results
The animals of group (B) showed decrease in appetite The site of inoculation become tender and swollen. -The clinical observations showed violent spasm , lasting lbr a few minutes and convulsive movement of the leet , these observations occurred (7 days) after second inoculation with Staph. aureus artd lasting until the time ol sacrifing -Histological examination of the group A.
The cerebral cortex is thrown into gyri and sulci like elsewhere in the human and other animals. The gray matter was a mixture of nerve cells and nerve fibers,neuroglia and blood vessels.
The following tlpes of the nerve cells are present in the cerebral cortex. (1) pyramided cells (2)stellate cells (3) fusioform cells(4)horizantal cells of cajal (5) cells of matedal (Fig 1,2). Group B (treated Group) wide spread of demyelination with swelling of axons in the white matter (Fig   3), focal necrosis of the nerve cells, atrophy of the nerve and glial cells associated ,with few leucocytic infiltration ,vaculations or pocket like appearance of most sites of the nervous system.

Discussion
Infection of the skin by the Staph. aureus was well established (3).It forms abscess and boils of the skin, endocaditis of the heart and meningitis of the brain membranes(l). A rabbit model for induction of the brain lesion or meningitis was applied to confirm the concept of the effect of the Staph. aureus on the brain tissue by inoculation of the bacteria subcutaneously.
The structural changes demonstrated in the brain tissue provided a confirmation for the relationship between the skin infection and brain lesion. The hypothesis for the effect of the bacillus or its toxin or both is occur in the form of toxic shock syndrome (11). In the present study , the neuronal damage of the brain tissue was not associated with any inflammation of the meninges , which may reflect the transmission ol the bacteria or its toxin or both via blood circulation to the brain , there is another route lor infection of meninges and brain tissue via cerebrospinal fluid (6). Blood brain barrier is well protection for the brain tissue (12). We inoculation. Two doses of the bacterial suspension (15) days interval in order to assure the breaking down of this barrier for aniving of the pathogen to the brain tissue. The presence of the extensive vaculation in the brain may consider as a result for degenerative condition of the neurons and glial cells (gliosis), followed by pus or oedematous formation init, and this concept agree with (13). of Staphylococcus pyogenes for man. Astudy of the problem of wound infections. Br.J.Exp. pathol .1957.3 8.573-86.