Studies on the pathogenesis of meningitis. II. Development of meningitis during pneumococcal bacteremia.

In a previous publication we described an experimental form of pneumococcal meningitis in dogs, which was produced by introduction of type III pneumococci into the subarachnoid space through a small midline burr hole placed equidistant between the coronal and occipital sutures (1). The infection produced in this manner involved the entire neuraxis and, with the exception of marked changes in the spinal cord, closely resembled that found in man. It seems unlikely, however, that entry from the external environment is the only means by which bacteria enter the subarachnoid space. An alternative possibility is that the meninges are infected by way of the blood stream. The present paper is concerned with the development of meningitis during pneumococcal bacteremia in dogs. With the exception of the early report by Bull (2) that intravenous administration of pneumococci to dogs was followed by meningitis, in most studies intravenous injection of a variety of microorganisms into rabbits, dogs, monkeys, and cats has not resulted in infection of the meninges (3-7). Weed, Wegeforth, Ayer and Felton (6, 8), however, regularly observed meningitis when cats were subjected to lumbar puncture during bacteremia with Aerobacter aerogenes, an encapsulated, gram-negative bacillus. Control animals given twice as many organisms but not subjected to lumbar puncture remained well. Infection developed only when cerebrospinal fluid (CSF) was removed 30 minutes before or after the injection of bacteria, and meningitis did not develop when lumbar puncture was performed outside this 30-minute interval. Infected animals generally became sick within 24 hours and died 24 to 48 hours later. A. aerogenes was used in