027 - Experimental Studies of the Nasopharyngeal Secretions from Influenza Patients X. the Immunizing Effects in Rabbits of Subcutaneous Injections of Killed Cultures of Bacterium pneumosintes

This study,¹ and those accompanying it (parts I-IX) seemed like a particularly exciting step forward in the understanding of influenza. Published about 4 years after the worst known epidemic of flu in history (1918 Spanish flu), people were understandably keen on discovering the cause and ways to prevent this disease.

Previous research had suggested bacterial pathogens as the culprit, such as Pfeiffer's bacillus (aka Bacillus influenzae, later named Haemophilus influenzae) or others, but these could not be reliably found in flu patients, nor did serum from patients always contain antibodies against the bacteria. Vaccines made from them (such as in 019 or 026) didn't reliably protect against the flu, though they may have helped with secondary pneumonia infections. It didn't help that research during the 1918 epidemic was mostly rushed and sloppy.

But then, four years later, two researchers at the Rockefeller Institute for Medical Research made an important discovery about influenza.

Experimenting on nasal washings from patients from the 1918 epidemic, they found that the disease could be transmitted to rabbits effectively, but no bacteria need be consistently present in the washings for the transmission to occur.² In addition, the washings could be filtered through a filter small enough to remove all known bacteria, and the resulting filtered product could still cause disease.³ This showed that the infectious agent was something smaller than known bacteria, but still capable of replication and spreading to new hosts.

These researchers isolated a tiny rod-shaped organism, often small enough to fit through the filter, that they could grow in the lab; they named it Bacterium pneumosintes.⁴ Unfortunately, many other researchers could not replicate the results of Olitsky and Gates,^5-7 though B. pneumosintes was later found to be a bacterial inhabitant of the human mouth and renamed Dialister pneumosintes,8,9 but the true agent of influenza was not discovered until the 1930s.

However, Olitsky and Gates went ahead and tried making a vaccine using this organism they discovered. They grew up two strains of it, one isolated from a patient in 1918 and one from a patient in a flu epidemic in 1922, killed these cultures with heat, and injected them into rabbits. The rabbits tolerated the vaccines pretty well, having some redness and swelling after the second of three doses.

When challenged with infectious bacteria, the results were as follows: two vaccinated rabbits and two controls were challenged with samples from rabbits previously infected with B. pneumosintes from previous experiments. The two controls got sick, while the two vaccinated did not.

Then another 17 vaccinated rabbits and 17 controls were challenged with cultures of B. pneumosintes, and 15 of the vaccinated rabbits did not get sick while the others did. So 88% effective. The two vaccinated rabbits that did get sick, and 10 of the ones that didn't, were also challenged with bacteria that cause secondary infections in flu patients (pneumococcus, Streptococcus haemolyticus, etc), and the 10 that didn't get sick were also protected against infection with these organisms, while the 2 that did were not, and succumbed.

So this shows, perhaps, that B. pneumosintes is indeed a pathogen, in rabbits at least, and a vaccine made from it protects rabbits from infection with it. Too bad it's not actually influenza.

Citations:
1. Olitsky, P. K. & Gates, F. L. Experimental Studies of the Nasopharyngeal Secretions from Influenza Patients X. the Immunizing Effects in Rabbits of Subcutaneous Injections of Killed Cultures of Bacterium pneumosintes. J Exp Med 36, 685–696 (1922).
2. Olitsky, P. K. & Gates, F. L. J Exp Med. 1921 January 31; 33(2): 125–145.
3. Olitsky, P. K. & Gates, F. L. J Exp Med. 1921 February 28; 33(3): 361-372.
4. Olitsky, P. K. & Gates, F. L. Experimental Studies of the Nasopharyngeal Secretions from Influenza Patients IV. Anaerobic Cultivation. J Exp Med 33, 713 (1921).
5. Andrewes, C. H., Laidlaw, P. P. & Smith, W. Influenza: Observations on the Recovery of Virus from Man and on the Antibody Content of Human Sera. Br J Exp Pathol 16, 566–582 (1935).
6. Garrod, L. P. Filter-Passing Anaerobes in the Upper Respiratory Tract. Br J Exp Pathol 9, 155–160.1 (1928).
7. Wilson, G. S. An Attempt to Isolate Bacterium pneumosintes from Patients Suffering from Influenza. The Lancet 209, 1123–1124 (1927).
8. Willems, A. & Collins, M. D. Phylogenetic Placement of Dialister pneumosintes (formerly Bacteroides pneumosintes) within the Sporomusa Subbranch of the Clostridium Subphylum of the Gram-Positive Bacteria. Int J Syst Bacteriol 45, 403–405 (1995).
9. Ghayoumi, N., Chen, C. & Slots, J. Dialister pneumosintes, a new putative periodontal pathogen. Journal of Periodontal Research 37, 75–78 (2002).