Inhibitory effect of cerebrospinal fluid on the growth of meningococci and pneumococci.

Initial cerebrospinal fluid (CSF) samples obtained from patients with pneumococcal meningitis usually contain far greater numbers of bacteria than initial CSF samples obtained from patients with meningococcal meningitis. Normal CSF was found to have an inhibitory effect on the growth of group A meningococci but not on type 1 pneumococci. The inhibitory effect of normal CSF was abolished by dialysis, indicating that the inhibitory factor has a low molecular weight. Heating normal CSF to 62.5 degrees C for 30 min resulted in a considerable reduction in the inhibitory effect, indicating that the inhibitory factor is heat labile.