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Several historic figures have been called father of microbiology:

Microbiology Pasteur image from New Medical Terms

Louis Pasteur

Athanasius Kircher (1602-1680), a German Jesuit who in 1646 used a lens system of his own design to observe, ‘…putrid material full of innumerable creeping animalcules.’ 

Anton van Leeuwenhoek (1632-1723), a Dutch lenscrafter who devised a single lens microscope through which in 1676 he observed bacteria and other microorganisms

• Louis Pasteur (1825-1895), a French biologist and chemist who disproved the theory of spontaneous generation in the mid-19th century. 

• Robert Koch (1843-1910), German physician, who built on Pasteur’s work by formulating the core assertions* on which medical microbiology was founded:

(1) The microorganism must be isolated from a diseased organism and grown in pure culture.

(2) The cultured microorganism should cause disease when introduced into a healthy organism.

(3) The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

*Initially, there were four postulates, but Koch realized that the plethora of exceptions to the first postulate: The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms, precluded its inclusion as a necessary criterion for linking a particular infection to a particular organism. 

Whilst Koch’s postulates were evoked in linking Helicobacter pylori, a relatively new bacterial pathogen, to peptic ulcers, they are more of historic interest than a sine qua non for proving causality. Some pathogens, even in Koch’s day, were linked to diseases even though the postulates weren’t fulfilled. That the postulates have not clearly linked HIV to AIDS has given rise to HIV/AIDS denialism. 

Medical microbiology is focused on preventing, diagnosing and treating infectious diseases, which are caused by five classes of pathogens: 

•Parasites, which can be divided into:

Microparasites–e.g., Plasmodium falciparum, and 

Macroparasites–e.g., Ascaris lumbricoides

• Fungi–e.g., Candida albicans, Coccidiodomycosis immitus

• Bacteria–e.g., Vibrio cholera, Treponema pallidum

• Viruses–e.g., HAV, HBV, HCV, rotavirus

• Prions–protein-only particles*

*Prions cause Creutzfeldt–Jakob disease, Gerstmann–Sträussler–Scheinker syndrome, fatal familial insomnia, kuru and multiple system atrophy. These conditions spread like viruses, are untreatable and are universally fatal. 

Microbiologists play a central role in preventing transmission of pathogens, as they are often ‘volunteered’ to act as clinical leads in infection control at the hospitals or medical centers where they have admitting privileges. Modes of transmission of pathogens include direct and indirect contact, aerosol droplets from coughing or sneezing, fecal–oral from contaminated food or water, airborne–e.g., spores, via vectors–P falciparum via mosquitoes, fomite transmission–e.g., common cold, and environmental–e..g., Legionella spp. 

microbiology antibiotic image from New Medical Terms

microbiology antibiotic susceptibility testing

The most effective method for reducing transmission of infections is obsessive and repeated hand washing. Effective hand hygiene is practiced far less than it should be and would, according to widely quoted figures, reduce hospital infections by more than 50%.  

The bulk of diagnostic microbiology consists of culturing clinical specimens in agar, determining the biochemical profile of those that grow as pure colonies and assessing their susceptibility to antibiotics by dropping antibiotic-impregnated disks on a “lawn” of bacteria grown on Mueller Hinton agar (image) and calculating the MIC (minimum inhibitory concentration) of the tested antibiotics. 

Medical microbiology is a subspecialty of pathology in the UK and requires, after completion of medical school, the requisite (two) years of so-called foundation (generalist) training, begun on graduating from medical school, followed by at least 4 and a half years of specialty training in microbiology, for a total of 6.5 years of training. The American equivalent is known as infectious disease, and is a subspecialty of internal medicine, requiring three years of post-medical school training in general (internal) medicine, followed by a two year fellowship in infectious disease.