Historical Ascepts of Medical Microbiology

History of medical microbiology

Till the end of the nineteenth century, many infectious diseases had been proven to have a bacterial origin..The process started in the twentieth century. But yet there remained many diseases of a common occurrence for which no bacterium could be found. These included smallpox, chickenpox, measles, and a common cold. the discovery of electron microscopy in 1934 by Ruska made an examination of viruses possible.The first human disease proved to have a virus origin was yellow fever

In the early stage, the causes of diseases were unknown and was thought to be caused due to the mistakes in previous lives.As time passes on, human developed the concept that the diseases were caused due to invisible living things.this was first discovered my Roger in the thirteen century.Medical microbiology began when human known to make lenses from the small pieces of glasses and be able to join them to produce magnification enough to make possible to the microorganisms to be seen.The discovery of microscope made the dream concepts real.Antony van Leeuwenhoek (1632-1723) designed a single lens microscope and finally showed the smallest agents capable of causing disease.he also named those agents as animalcules.these animalcules are now classified as various pathogen entities such as bacteria,virus and so on.therefore,organisms that are not visible or seen to the naked eye are known as microorganisms.

For many years it was believed that the microorganisms arose from dead, mostly decomposed
organic matter. This was known as the theory of spontaneous generation theory.the theory was disproved by Louis Pasteur.the discovery of Germ theory of disease contributes to the rapid development of medical microbiology

Antimicrobial agents

With the detection,identification, as well as confirmation of bacteria as causative agents of human diseases, efforts and various researchers, were made to develop effective agents which could destroy bacteria in the body of the man without damaging the host tissue.important work was done by Paul Ehrlich who is known as the father of chemotherapy. In the 1900s he totally cured one form of trypanosomiasis in rats with the dye trypan red and another form in mice with an organic arsenic-containing inorganic compound, alkoxyl.In 1910, Ehrlich successfully cured syphilis using compound '606'’ (dioxydiaminoarsenobenzol dihydrochloride) and called it Salvarsan. Fleming discovered penicillin and Waksman streptomycin. Subsequently,many molds and yeast I have been used as a source of antimicrobial drugs.

Discovery of viruses

By 1940, growth in tissue culture of susceptible mammalian cells was proved. The availability of well-defined cell lines has now replaced tedious methods of growing viruses in the living animals.

Nobel prize winners and contributors

A number of Nobel laureates in Medicine and Physiology were awarded this prize for their work in Microbiology and Immunology .

During the last quarter of the nineteenth century, a mere succession of discovering was reported which had a bearing on the relation of bacteria to human and animal diseases.

. Table 1–1. Discoveries of bacteria in 19th Century

Aspects of medical microbiology

Infectious diseases are caused by subcellular infectious entities (prions,viruses), prokaryotic bacteria, eukaryotic fungi and protozoans, metazoan animals, such as parasitic worms (helminths), and some arthropods. Definitive proof that one of these factors is the cause of a given infection is demonstrated by the fulfillment of the three Henle-Koch postulates. For technical reasons, a number of infections cannot fulfill the postulates in their strictest sense as formulated by R. Koch, in these cases a modified form of the postulates is applied.

The History of Infectious Diseases

The Past

Infectious diseases have been known for thousands of years, although accurate information on their etiology has only been available for about a century. In the medical teachings of Hippocrates, the cause of infections occurring frequently

in a certain locality or during a certain period (epidemics)was sought in “changes” in the air according to the theory of miasms. This concept, still reflected in terms such as “swamp fever” or “malaria,” was the predominant academic opinion until the end of the 19th century, despite the fact that the

Dutch cloth merchant A. van Leeuwenhoek had seen and described bacteria as early as the 17th century, using a microscope he built himself with a single convex lens and a very short focal length. At the time, general acceptance of the notion of “spontaneous generation”—creation of life from dead organic material—stood in the way of implicating the bacteria found in the corpses of infection victims as the cause of the deadly diseases. It was not until Pasteur disproved the doctrine of spontaneous generation in the second half of the 19th century that a new way of thinking became possible. By the end of that century, microorganisms had been identified as the causal agents in many familiar diseases by applying the Henle-Koch postulates formulated by R. Koch in 1890.

The Henle–Koch Postulates

The postulates can be freely formulated as follows:

• The microorganism must be found under conditions corresponding to the pathological changes and clinical course of the disease in question.
• It must be possible to cause an identical (human) or similar (animal) disease with pure cultures of the pathogen.
• The pathogen must not occur within the framework of other diseases as an “accidental parasite.”

These postulates are still used today to confirm the cause of an infectious disease. However, the fact that these conditions are not met does not necessarily exclude a contribution to disease etiology by a pathogen found in context. In particular, many infections caused by subcellular entities do not fulfill the postulates in their classic form.

The Present

The frequency and deadliness of infectious diseases throughout thousands of years of human history have kept them at the focus of medical science. The development of effective preventive and therapeutic measures in recent decades has diminished and sometimes eliminated entirely, the grim epidemics of smallpox, plague, spotted fever, diphtheria, and other such contagions. Today we have specific drug treatments for many infectious diseases. As a result of these developments, the attention of medical researchers was diverted to other fields: it seemed we had tamed the infectious diseases. Recent years have proved this assumption false. Previously unknown pathogens causing new diseases are being found and familiar organisms have demonstrated an ability to evolve new forms and reassert themselves. The origins of this reversal are many and complex: human behavior has changed, particularly in terms of mobility and nutrition. Further contributory factors were the introduction of invasive and aggressive medical therapies, neglect of established methods of infection control and, of course, the ability of pathogens to make full use of their specific genetic variability to adapt to changing conditions. The upshot is that physicians in particular, as well as other medical professionals and staff, urgently require a basic knowledge of the pathogens involved and the genesis of infectious diseases if they are to respond effectively to this dynamism in the field of infectiously.

Pathogen

Subcellular Infectious Entities

Prions (proteinaceous infectious particles). The evidence indicates that prions are protein molecules that cause degenerative central nervous system (CNS) diseases such as Creutzfeldt-Jakob disease, kuru, scrapie in sheep, and bovine spongiform encephalopathy (BSE) (general term: transmissible spongiform encephalopathies [TSE]).

Viruses. Ultramicroscopic, obligate intracellular parasites that:

— contain only one type of nucleic acid, either DNA or RNA,

— possess no enzymatic energy-producing system and no protein-synthesizing

apparatus, and

— force infected host cells to synthesize virus particles.

References:

D greenwood, Slack RCB and J Peutherer. Medical microbiology. 2001.

JG College, AG Fraser and BP Marmion. Practical Medical microbiology. Fourteenth Edition. Churchill Livingstone, 1996.

JP Micheal, ECS Chan and NR Krieg. Microbiology. Fifth Edition. Delhi: Mcgraw-hill, 1993.

M Cheesbrugh. Medical laboratory manual for tropical countries. London, 2007.