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Koch’s Postulates and Ehrlich’s ‘Magic Bullet” : 
Specific Causation, Treatment and Prevention- Doctrines of Specificity in Medicine. By: Elizabeth Griffiths, MS2
 
How do we treat disease? AXIOM: Our interpretation of Causality determines  our therapeutic intervention. 
A brief review of medicine until the mid1600s- older concepts of causality 
Pasteur and Koch- Early bacteriology and Koch’s Postulates 
Paul Ehrlich- The birth of immunology and the ‘Magic Bullet’
 
Older Concepts of Disease The Magico-religious concept of disease:  This interpretation leads to treatments which depend largely upon exorcisms, prayer and atonement with the assumption that disease has been sent as a punishment or curse.
       - In Mesopotamia disease was interpreted as the hand of god: disease was the result of ‘… spirit invasion, sorcery, malice or the breaking of taboos; sickness was both a judgement and a punishment….’(Porter 46).
       - The Egyptians believed one was born healthy and disease originated from demons or intestinal putrefaction.  Herodotus mentions that three days each month were laid set aside for evacuating the body with emetics and enemas. 
 
Aristotle suggested ‘four causes’: 1) The material cause, 2) The formal cause (or blueprint) 3) The moving or efficient cause (the agent) 4) the final cause (the purpose or outcome). 
         -For every disease there must be some origin, changing the concept of disease and its treatment from a religious to an observational/scientific endeavor
The Humoral Doctrine of disease:
       -The Hippocratics believed that illness stemmed from an ‘imbalance’ in the bodily humors- black bile, yellow bile, blood, phlegm.  Treatments were thus largely aimed at reestablishing balance- bleeding to eliminate excess blood, exercise, and purging were all standard therapies.  
         - Galen seized the Humoral concept of disease and his ideas dominated medicine for almost a millennium.  In 1481 the following medical curriculum was taught at the University of Tübingen:
First year: Galen’s Ars Medica, Avicenna’s Treatise on Fevers
Second year: Avicenna (Anatomy and physiology), Rhazes Ninth book(local pathology)
Third year: Aphorisms of Hippocrates, Galen
 
After 1600 Physicians saw manifestations of disease, but the cause was still humoral imbalance-
       -In 1694 when an autopsy was performed on Marcello Malpighi who first demonstrated capillaries post mortem showed hemorrhage into the right ventricle of the brain- but the cause? ‘… glands in the body had  poured into the blood two humors, which when they reached the brain corroded the artery and caused the bleeding….’ Giorgio Baglivi(1668-1707) ( from Hudson 104)
In 1761 Giovanni Batista Morgagni published On the Seats and Causes of Disease
         - This work demonstrated the value of clinico-pathologic correlation, but more importantly it localized the cause of disease to organs rather than to the bodily humors- but this really didn’t change the way we TREATED disease.
The Paris School and all its developments would continue this tradition, but observation didn’t really bring about a new method of dealing with disease in terms of treatment.
 
Pasteur and Lister Before 1860 there were many people who believed that fermentation and putrefaction were caused by living organisms, but no one had PROVED that this was the case and there was significant debate.
Between 1860 and 1870 Pasteur demonstrated that fermentation was caused by micro-organisms, that there were different organisms which would cause different types of fermentation, and that these organisms were UBIQUITOUS. 
In 1865 Joseph Lister heard of Pasteur’s discovery and reasoned that if fermentation was caused by these animalculae putrefaction of wounds might also be.  This led him to institute the use of carbolic acid as a disinfectant with stunningly successful results-- a 50% drop in mortality. 
Despite Lister’s results many people remained unconvinced (perhaps because this might mean acceptance of the germ theory of disease-  Semmelweis’ (ca 1847) reception had already shown how popular this was.)
 
Setting the Stage In the middle of the 1870 microscopy had developed considerably making it possible to visualize Pasteur’s micro-organisms, although not their intracellular structures.
Additionally the German dye industry had produced a number of compounds which were able to stain both tissues and micro-organisms with differential affinity.
These innovations would facilitate the work that Robert Koch was about to begin while working in his back yard laboratory in Eastern Prussia.  
 
Koch’s Life Robert Koch(1843-1910)
3rd of 13 children
Trained with Jacob Henle at the Göttingen Medical School
After the Franco-Prussian war he was assigned the district physician for Wollstein, a town in Polish Prussia, there he became intensely interested in bacteriology and assembled his own laboratory
In 1873 he began to investigate Anthrax, which was especially rampant in Wollstein.
 
Koch was largely responsible for the scientific establishment of bacteriology
        -In April of 1876 traveled to Breslau  where he demonstrated his Anthrax research: Using a method of his own invention Koch was able to conclusively demonstrate the existence of anthrax spores and to trace the complete life cycle of the organism-- no one had done this for any other bacterium. At this demonstration J.F. Cohnheim declared, ‘There is nothing left to prove.  I regard it as the greatest discovery ever made with micro-organisms.’(Carter xiv)  
Emphasized that PURE cultures were necessary A CONSUMATE technician
        -He photographed his bacteria, a great improvement over the contemporary practice of hand drawn sketches.
        -in 1881 he presented his development of the poured bacterial medium(agar, a seaweed byproduct), as well as a number of other technical innovations-  Pasteur himself is said to have rushed forward saying ‘C’est un grand progrès!’ (Carter xiv).
 
Formalized procedures for establishing disease causation (Koch’s Postulates) 
Began his investigations of tuberculosis in 1881 and in 1882 announced his initial results, he had indeed identified the causative agent in tuberculosis, (He received the Nobel prize for this work in 1908).
Eventually with the help of his colleagues he was able to identify the causative agents of infected wound diseases, tuberculosis, cholera, typhoid, and diphtheria.  
His reputation was irrevocably damaged in 1890 when he announced tuberculin, that was believed to inhibit the growth of the tubercule bacilli.  It was later proven that tuberculin, although excellent for diagnosis was not useful therapeutically. It was further damaged in 1893 when he, then 50 fell in love with a 21 year old actress and divorced his wife. 
 
 
Koch’s Postulates 1) The Parasit occurs in every case of the disease.
2) The Parasit does not occur in other diseases or non-pathogenically
3) After being fully isolated from a diseased animal and repeatedly grown in pure culture, the Parasit can induce the disease by being introduced into a healthy animal.
 
Weaknesses of the Postulates A) There are many diseases for which even Koch himself could not satisfy all three postulates.
B) Asymptomatic infections (Carriers) were known even in Koch’s time.
C) Many viral diseases do not fulfil these postulates- e.g.:Epstein-Barr virus and its association with Burkitt’s Lymphoma, Hodgkin’s disease, and nasopharyngeal carcinoma.
D) Many viral infections lead to the same illness- Rhinovirus, adenovirus, RSV, coronavirus.
E) Prion diseases are not ‘culturable’ since they aren’t alive.  i.e. mad cow disease, Kuru, sheep scrapies.
F)Some infectious diseases take many years to produce symptoms.
 
Weaknesses Cont. G) Multiple factors may contribute to the development of disease:
         - nutrition, diabetes, genetics, concurrent viral illness, immune status, etc.
H) Immune reactions were not addressed by Koch
         - mitral stenosis, acute glomerulonephritis following streptococcal infection.
I) The proximate insult may be far less damaging than collateral /side effects which may develop later.
         - subacute sclerosing panencephalitis, post-polio syndrome.
J) The power of the mind over the body?
K) ‘Essential’ or ‘idiopathic conditions?
 
Ehrlich’s Life Born in 1854 to working class parents
Enrolled at Breslau University, but transferred to the University of Strasbourg where he became fascinated with chemistry--he is quoted as having said, ‘I…believe that my real natural endowment lies in chemistry… the benzene rings and structural formulae…disport themselves in space before my mind’s eye’ (Wick)
After the appropriate premedical education he returned to Breslau to pursue his medical education where he pursued research involving the interaction of aniline dyes with human tissues.
 
Ehrlich’s thesis for his MD was entitled ‘Contributions to the Theory and Practice of Histological Staining’ during his research he described a new cell type in human tissues which contained numerous basophilic granules- he proposed that it be called a ‘mast’ cell.
After medical school he worked at the Charité Hospital in Berlin.  Under the direction of Freidrich von Freirich, who recognized his genius Ehrlich was responsible for analysis of all inpatient blood smears, a task which pleased him and which allowed him to develop a consummate expertise in morphologic hematology. He later published a comprehensive text on the differential staining qualities of blood cells.  Additionally during this period he developed the precursor to the current acid-fast mycobacterial stain and the ‘Ehrlich method’ for urobilinogen quantitation, all of this before he was 30. Ehrlich’s Accomplishments
 
Ehrlich’s Accomplishments Cont. 
When von Freirich died in 1885 he was replaced by Karl Gerhardt, described by Wick as an, ‘…autocratic, narrow-minded, and professionally deficient man…[who] interfered in Ehrlich’s research, making it progressively more difficult for him to think creatively…’(330).
In 1888 Ehrlich contracted tuberculosis and left the Charité for Egypt, before he went, however he submitted to a course of Koch’s ‘tuberculin treatment’ and it is this which first interested him in immunology
Ehrlich developed a method to titer the antibody strength in any given serum.  This development stemmed from the work of his colleague Emil von Behring who was trying to develop antidiphtheria toxin for clinical use.  Ehrlich’s contribution allowed the standardization of the antibody and calculation of a reproducible dose.  Von Behring later cheated Ehrlich out of the profits from the sale of diphtheria antitoxin.  Ehrlich would bitterly criticize him for the rest of his life.
In 1899 Ehrlich was appointed director of the Prussian State Antitoxin Institute in Steglitz.  
 
From 1890-1899 Ehrlich began to formulate his ‘key-in-lock model for antibody/antigen binding.  His theory proposed a stereospecific interaction based upon covalent, rather than ionic bonds.
         --debate over this raged for years.  Ehrlich was right about stereospecificity, but wrong about the irreversible covalent bonds. 
Ehrlich postulated that there existed a third factor (besides antibody and antigen) which bound to a part of the antibody distinct from the antigen binding site
          --  Today we recognize complement and know that it binds antibody on the Fc portion of the antibody.  Ehrlich was incorrect, however in proposing that there were several distinct complements one for each antibody subclass and also that complement bound antibody independently of its interaction with antigen.
 
Ehrlich’s ‘Magic Bullet’ At 45 Ehrlich changed directions again, this time to focus on pharmacology.  This work was actually an extension of his immunological work he proposed that foreign microbes might posses biochemically unique binding sites whose blockade could result in targeted destruction of the invading microbe without harm to healthy tissues.  Here was his ‘magic bullet’ concept, still the inspiration for many of today’s therapies. 
In 1909 Ehrlich and his colleague Sachahiro Hata became intrigued by the arsenical 606 which was found to be highly effective against yaws and relapsing fever-- syphilis.  At last he had achieved the ‘magic bullet’ for this disease.
However, the development resulted in a surprising backlash which would ultimately cause the end of Ehrlich’s career.
          -- “He became the object of vituperation, denouncement and discredit.  ‘The pox’ was seen as the deserved punishment for promiscuity. In response to a possible cure the church, politicians and even some scientists responded by reviling 606 and its creators as the devil’s pawn” (Wick 332).  This response seems to have damaged Ehrlich.  He ceased to participate in scientific research and died of a CVA in 1915.    
 
The ‘Magic Bullet,’ an Illusive Goal 
Although Ehrlich  never succeeded in producing a single dose which would be lethal to the parasite while sparing the host, his ideas fostered a search for ‘magic bullets’ which would be effective for other bacteria.
The first of these would be the sulfonamides, followed by penicillin and many others. 
However, as we examine illness today it is clear that a single ‘magic bullet’ will not be effective.  Most obviously with tuberculosis, and recently with HIV disease we have found that several ‘bullets’ are more effective than just one.  Moreover these bullets are invariably more damaging than we would like them to be.
 
What are we left with? It is clear that the ideals for definition and treatment of disease presented by Koch and Ehrlich at the turn of the century are of limited direct application.  This does not mean that they are not and have not provided a valid conceptual framework.
As Ruy Perez-Tamayo, MD states in his Epilogue to Mechanisms of Disease:
       “… after all these centuries of recorded history, and many more preceding our short and ridiculous attempt at keeping track of all human frailties and greatness, it has emerged that disease, as all other manifestations of living beings, is life itself, and nothing more.”
 
References: 1. Carter, K.C.. Essays of Robert Koch. Westport, Connecticut: Greenwood P, 1987.
2. Erickson, R.P.. From ‘magic bullet’ to ‘specially engineered shotgun loads’: The new genetics and the need for individualized pharmacotherapy.  BioEssays. 20:683-685 (1998).
3. Evans, A.S.. Causation and Disease: The Henle-Koch Postulates Revisited.  Yale J Biol Med. 49:175-195 (1976).
4. Hudson, R.P.. Disease and Its Control: The Shaping of Modern Thought.  New York: Praeger, 1983.
5. Metchnikoff, E.. The Founders of Modern Medicine: Pasteur, Koch, Lister. New York: Walden, 1939.
6. Perez-Tamayo MD, R.. Mechanisms of Disease: An Introduction to Pathology. Philadelphia: WB Saunders, 1961.
7. Porter, R.. The Greatest Benefit to Mankind: A medical history of humanity.  New York: WW Norton, 1997.
8. Silverstein, A.M.. Paul Ehrlich’s Passion: The Origins of his Receptor Immunology.  Cell Imunol. 194:213-221 (1999).
9. Wick MD, M.R.. Retrospective-Paul Ehrlich: The Prototypic Clinical Pathologist. Am J Clin Pathol. 90:329-332 (1988).