The ability of B. influenzae to reduce nitrates to nitrites may be used as a rapid diagnostic test in influenzal meningitis. The organisms which commonly cause meningitis, such as meningococci, tubercle bacilli and streptococci, are not nitrate reducers. Staphylococci and various members of the colon-typhoid group, though nitrate reducers, rarely cause meningitis, and are easily differentiated from the influenza bacillus, the most frequent cause of meningitis among the nitrate-reducing bacteria.
Rivers1 found nitrate reduction in fifteen meningitic and eighteen respiratory strains of B. influenzae. Jordan and Reith2 tested 287 strains of B. influenzae of the respiratory type and found that every one reduced nitrates to nitrites. They regarded nitrate reduction as an important differential criterion for this organism.
Rivers3 proposed a direct indol test on the spinal fluid for the rapid diagnosis of influenzal meningitis, based on Jordan's4 observations that most strains of B. influenzae produced