Pneumococcus
I believe there is a list of bacterial pathogens which are really true classics of the bacteriology field. They have a rich historical background and knowledge of these diseases has evolved in such a way over the past ~100 years that every bacteriologist must have a good understanding of them. Currently, my list stands as follows:
- Mycobacterium tuberculosis
- Treponema pallidum (syphilis)
- Brucella melitensis (brucellosis)
- Streptococcus pneumoniae
I have kept this list purposefully austere, and will admit bacteria over time, if they have done enough to pass the strict admission criteria.
Bacteriologists have known about the pneumococcus since 1881, when Sternberg and Pasteur independently described it in the US and France respectively (in the same year). The story of Sternberg’s discovery is particularly appealing. He was working on finding the cause of malaria and one of his experiments involved injecting rabbits with swamp samples from New Orleans. For these experiments, he also injected “control rabbits” with his own saliva. Much to his surprise, these control rabbits rapidly died a horrible death in 48 hours (I will need to dig up his original reports to see what happened to the rabbits injected with swamp fluid). He must have been fascinated by this surprise discovery, as he went on to titrate the concentration of saliva that caused rabbit death (1.25c3 to 1.75c3 injected subcutaneously). He also demonstrated that the diplococcic pneumococcus was the cause of death.
The pneumococcus has many features that I argue warrant its admission to this small list of pathogens:
- it remains well identified using basic good old-fashioned bacteriological techniques (which are perhaps better in some ways than modern techniques)
- modern medicine has had a great impact on infection over the last century through various different therapies and vaccination
- it is a multisystem pathogen, that disseminates haematogically and forms biofilm
- there is a complex interplay between the germ and the body’s immune response, ranging from colonisation to fatal infection
We rightfully think of penicillin as having revolutionised treatment of pneumococcal infection. Mortality after meningitis was 100%, while pneumococcal pneumonia caused death in 35% of infected patients. The success of penicillin in driving down mortality overshadows the reality that successes were achieved prior to widespread use of penicillin. Sulfonamides (which unfortunately are hindered by frequent emergence of resistance during therapy) and concentrated rabbit serum (these rabbits have really had a bad time with the pneumococcus) were deployed with success. Violini et al reported in 1941 mortality rates of 9.8% and 5.3% for serotherapy and sulfonamide chemotherapy respectively, compared with 38.4% for control cases.
The pneumococcus also has an important contribution to the field of antimicrobial resistance, but an unexpected one. While the development of resistance to penicillin is the most important development in the clinical practice and treatment of pneumococcus, the pneumococcus was the first bacterium to which antimicrobial resistance was described. The agent was optochin, and resistance was described in 1912. Curiously this agent still has an important use in the laboratory - susceptibility to optochin is used as a quick and dirty way to identify Streptococcus pneumoniae (ironically!). It has no clinical uses nowadays.
I welcome nominations for bacteria to admit to this prestigious list. I will attempt to follow this article up with polemics for the others that are currently on it.
I close with this excellent quote:
Pneumococcus is an altogether amazing cell. Tiny in size, simple in structure, frail in make-up, it possesses physiological functions of great variety, performs feats of extraordinary intricacy and, attacking man, sets up a stormy disease so often fatal that it must be reckoned as one of the foremost causes of human death. Furthermore, living or dead, whole or in part, on entering the animal body, Pneumococcus starts a train of impulses, stimulating all reactions grouped under those inclusive phenomena known as immunity.
Benjamin White, The Biology of Pneumococcus, 1938
Further reading:
Austrian, R., 1999. The pneumococcus at the millennium: not down, not out. J Infect Dis 179 Suppl 2, S338-341. https://doi.org/10.1086/513841
Austrian, R., 1981. Pneumococcus: the first one hundred years. Rev Infect Dis 3, 183–189. https://doi.org/10.1093/clinids/3.2.183
Volini, I.F., Levitt, R.O., O’Neil, H.B., 1941. Serotherapy and Chemotherapy of Pneumococcus Pneumonia. Medical Clinics of North America 25, 205–217. https://doi.org/10.1016/S0025-7125(16)36628-7