Introduction to Microbiology

A. Definition: Microbiology

Microbiology is a branch of biology, it is the study of microorganisms. It can be defined as the biology of microscopic organisms as the microorganisms in microbiology visible only under a microscope. Microbiology covers several disciplines, including virology (study of viruses), bacteriology (study of bacteria), mycology (study of fungi) and parasitology (study of parasites).

Each of these disciplines may include but is not limited to studies of infectious disease-causing microorganisms only. For example, specialties within microbiology may include microbial physiology (i.e., microbial growth, metabolism, structure), microbial genetics and evolution, environmental microbiology (i.e., microbial ecology), industrial microbiology (i.e., industrial fermentation, wastewater treatment) and food microbiology (i.e., use of microbes for food production, fermentation).

Microorganisms are widespread in the nature. Some bacteria inhabit the inner and outer surfaces of the human body and these are non-pathogenic micro-organisms as they produced no disease. The bacteria of the small and large intestine are even useful digestive aid since it provides among other things important for blood clotting vitamin K. Such a union between two organisms is called symbiosis.

There are microorganisms that act cause disease and are therefore pathogenic, for example the causative agent of bacterial infection and viral diseases. Living beings that live at the expense of another organism are called a parasite such as arthropods and worms.

 

B. Classification of microbiology

1.  Bacteria are unicellular organisms, they come in many shapes and sizes and are either a parasite or live independently.  Common shapes are rod-shaped (bacillus), sphere-shaped (coccus) and helix-shaped (spirilla). These shapes are caused by the growth of the cell wall of the bacterium. Bacteria multiply in a straightforward manner which each single celled bacterium grows until there is enough material to form two separate bacteria. The one parent bacterium then splits into 2 progeny bacteria. Many bacteria can actively move through small appendages (flagella). There are 2 types of bacteria, aerobic bacteria which need oxygen to live and anaerobic bacteria that live without oxygen. Antibiotics can usually kill them. An example of bacteria is meningitis and pneumonia.

 

2.   Viruses are microscopically small and are the simplest microbiological entity. A virus is not an independent living organism and needs a host cell to replicate. They are sub-microscopic parasitic particles of nucleic acid (RNA or DNA) that are wrapped in protein. It has no cell structure but rather consist of a protein coat (capsid), nucleic acids, which contain the genetic information and possibly a case. Viruses can reproduce only by using living cells. They penetrate to it with their nucleic acids into cells and alter cell metabolism so that it forms new viruses - so call this kind cell parasites. The affected cells are called the host cells, they perish in consequence of virus infection in the rule. Viruses are immune to antibiotics and are spread in the air or by direct contact. They can lead to serious or sometimes deadly diseases such as AIDS.

 

3.   Mushrooms (fungi) as the plants have a rigid cell wall, a nucleus and are motile but has no chlorophyll so they are not capable of photosynthesis which means they cannot use light to build energy-rich compounds. Fungi reproduce by spores and are about ten times larger than bacteria. They live by absorbing certain nutrients from any organic matter. There are over 120,000 different species of fungi that cause of which about 100 human diseases. Fungal infections commonly indicate a defensive weakness of the patient. Penicillin is made from a fungus.

 

4.   Protozoa is a single celled organism which is able to move and will feed on any organic compound of carbon and nitrogen, for example an amoeba. They has an identifiable nucleus and can be parasites or live independently. They are usually found in water or soil. Protozoa have different shapes and will produce asexually. They can inhabit the human body for example in the large intestine as a parasite.

 

5.   Algae are photosynthetic organisms of a group which live mostly in water. It includes the different seaweeds. Algae are different to plants because they have no true stems, roots or leaves. Algae also cause red tide, which can be fatal to fish and people eating contaminated shellfish. They will reproduce asexually.

 

C. History of Microbiology

1. Antonie van Leeuwenhoek (1632 – 1723)

 

Van Leeuwenhoek was a Dutch textile merchant who became a pioneer of microbiology.

 

Antonie van Leeuwenhoek was born in Delft on 24 October 1632. In 1648, van Leeuwenhoek was apprenticed to a textile merchant, which is where he probably first encountered magnifying glasses, which were used in the textile trade to count thread densities for quality control purposes. Aged 20, he returned to Delft and set himself up as a linen-draper. He prospered and was appointed chamberlain to the sheriffs of Delft in 1660, and becoming a surveyor nine years later.

 

In 1668, van Leeuwenhoek paid his first and only visit to London, where he probably saw a copy of Robert Hooke's 'Micrographia' (1665) which included pictures of textiles that would have been of interest to him. In 1673, he reported his first observations - bee mouthparts and stings, a human louse and a fungus - to the Royal Society. He was elected a member of the society in 1680 and continued his association for the rest of his life by correspondence.

In 1676, van Leeuwenhoek observed water closely and was surprised to see tiny organisms - the first bacteria observed by man. His letter announcing this discovery caused widespread doubt at the Royal Society but Robert Hooke later repeated the experiment and was able to confirm his discoveries.

As well as being the father of microbiology, van Leeuwenhoek laid the foundations of plant anatomy and became an expert on animal reproduction. He discovered blood cells and microscopic nematodes and studied the structure of wood and crystals. He also made over 500 microscopes to view specific objects.

He also discovered sperm, which he considered one of the most important discoveries of his career and described the spermatozoa from molluscs, fish, amphibians, birds and mammals, coming to the novel conclusion that fertilisation occurred when the spermatozoa penetrated the egg. Van Leeuwenhoek died on 30 August 1723.

 

2. Edward Jenner (1749 – 1823)

 

Jenner was an English doctor, the pioneer of smallpox vaccination and the father of immunology.

 

 Edward Jenner was born in Berkeley, Gloucestershire on 17 May 1749, the son of the local vicar. At the age of 14, he was apprenticed to a local surgeon and then trained in London. In 1772, he returned to Berkeley and spent most the rest of his career as a doctor in his native town.

In 1796, he carried out his now famous experiment on eight-year-old James Phipps. Jenner inserted pus taken from a cowpox pustule and inserted it into an incision on the boy's arm. He was testing his theory, drawn from the folklore of the countryside, that milkmaids who suffered the mild disease of cowpox never contracted smallpox, one of the greatest killers of the period, particularly among children. Jenner subsequently proved that having been inoculated with cowpox Phipps was immune to smallpox. He submitted a paper to the Royal Society in 1797 describing his experiment, but was told that his ideas were too revolutionary and that he needed more proof. Undaunted, Jenner experimented on several other children, including his own 11-month-old son. In 1798, the results were finally published and Jenner coined the word vaccine from the Latin 'vacca' for cow.

Jenner was widely ridiculed. Critics, especially the clergy, claimed it was repulsive and ungodly to inocculate someone with material from a diseased animal. A satirical cartoon of 1802 showed people who had been vaccinated sprouting cow's heads. But the obvious advantages of vaccination and the protection it provided won out and vaccination soon became widespread. Jenner became famous and now spent much of his time researching and advising on developments in his vaccine. Jenner carried out research in a number of other areas of medicine and was also keen on fossil collecting and horticulture. He died on 26 January 1823.

 

3. Louis Pasteur (1822 – 1895)

 

Pasteur was a French chemist and biologist who proved the germ theory of disease and invented the process of pasteurisation.

 

 Louis Pasteur was born on 27 December 1822 in Dole in the Jura region of France. His father was a tanner. In 1847, he earned a doctorate from the École Normale in Paris. After several years of research and teaching in Dijon and Strasbourg, in 1854, Pasteur was appointed professor of chemistry at the University of Lille. Part of the remit of the faculty of sciences was to find solutions to the practical problems of local industries, particularly the manufacture of alcoholic drinks. He was able to demonstrate that organisms such as bacteria were responsible for souring wine and beer (he later extended his studies to prove that milk was the same) and that the bacteria could be removed by boiling and then cooling the liquid. This process is now called pasteurisation.

Pasteur then undertook experiments to find where these bacteria came from and was able to prove that they were introduced from the environment. This was disputed by scientists who believed they could spontaneously generate. In 1864, the French Academy of Sciences accepted Pasteur's results. By 1865, Pasteur was director of scientific studies at the École Normale, where he had studied. He was asked to help the silk industry in southern France, where there was an epidemic amongst the silkworms. With no experience of the subject, Pasteur identified parasitic infections as the cause and advocated that only disease-free eggs should be selected. The industry was saved.

Pasteur's various investigations convinced him of the rightness of the germ theory of disease, which holds that germs attack the body from outside. Many felt that such tiny organisms as germs could not possibly kill larger ones such as humans. Pasteur now extended this theory to explain the causes of many diseases - including anthrax, cholera, TB and smallpox - and their prevention by vaccination. He is best known for his work on the development of vaccines for rabies. In 1888, a special institute was founded in Paris for the treatment of diseases. It became known as the Institute Pasteur. Pasteur was its director until his death on 28 September 1895. He was a national hero and was given a state funeral.

 

4. Joseph Lister (1827 – 1912)

 

Joseph Lister was a British Surgeon who is credited as being the 'father of antiseptic surgery'.

 

 Joseph Lister did not discover a new drug but he did make the like between lack of cleanliness in hospitals and deaths after operations. Lister was born in 1827 and died in 1912. As Professor of Surgery at Glasgow University, he was very aware that many people survived the trauma of an operation but died afterwards of what was known as ‘ward fever’.

 

Work on ward cleanliness and the link between germs and good post-operative health had already been studied by a Hungarian doctor called Ignaz Semmelweiss. He argued that if a doctor went from one patient to another after doing surgery, that doctor would pass on to the next visited patient a potentially life threatening disease. He insisted that those doctors who worked for him wash their hands in calcium chloride after an operation and before visiting a new patient.

Deaths on the wards Semmelweiss was in charge of fell from 12% to just 1%. But despite this, he came up against the conservatism of those who dominated Hungarian medicine and his findings were ignored. Semmelweiss died in 1865 of blood poisoning.

In 1865, Lister read about the work done by Louis Pasteur on how wine was soured. Lister believed that it was microbes carried in the air that caused diseases to be spread in wards. People who had been operated on were especially vulnerable as their bodies were weak and their skin had been cut open so that germs could get into the body with more ease.

Lister decided that the wound itself had to be thoroughly cleaned. He then covered the wound with a piece of lint covered in carbolic acid. He used this treatment on patients who had a compound fracture. This is where the broken bone had penetrated the skin thus leaving a wound that was open to germs. Death by gangrene was common after such an accident. Lister covered the wound made with lint soaked in carbolic acid. His success rate for survival was very high.

Lister then developed his idea further by devising a machine that pumped out a fine mist of carbolic acid into the air around an operation. The number of patients operated on by Lister who died fell dramatically.

 

5.   Robert Koch (1843 – 1910)

 

Robert Koch was a German physician who dedicated his life to finding the causes of infectious diseases

Robert Koch was born in 1843. Koch worked on anthrax and tuberculosis (TB) and he further developed the work of Louis Pasteur. Koch came from a poor mining family and it took him a lot of determination to get a university place where he first studied mathematics and natural science and then studied medicine.

Pasteur was convinced that microbes caused diseases in humans but his work on cholera had failed. He was never able to directly link one microbe with a disease but Koch succeeded in doing this.

Koch was a doctor and he had a detailed knowledge of the human body – something that Pasteur, as a research scientist – lacked. He was also skilled in experiments, the result of his work in natural sciences. Qualities that also proved to be important were his ability to work for long periods of time and his patience. However, Koch was also difficult to work with and could not tolerate anyone telling him that his theories were wrong.

In 1872, Koch became district medical officer for a rural area near Berlin. He started to experiment with microbes in a small laboratory he had built for himself in his surgery. The first disease that Koch investigated was anthrax. This was a disease that could seriously affect herds of farm animals and farmers were rightly in fear of it. Other scientists had also been working on anthrax. In 1868, a French scientist called Davaine had proved that a healthy animal that did not have anthrax could get the disease if it was injected with blood containing anthrax. Koch developed this work further and for three years he spent all his spare time finding out what he could about the disease, including its life cycle.

Koch found out that the anthrax microbe produced spores that lived for a long time after an animal had died. He also proved that these spores could then develop into the anthrax germ and could infect other animals. After this, Koch moved onto germs that specifically affected humans. In 1878, he identified the germ that caused blood poisoning and septicemia. He also developed new techniques for conducting experiments that influenced the way many other scientists carried out their experiments. He knew that infected blood contained the septicemia germ but he could not see these germs under a microscope, and therefore other scientists were unlikely to believe what he thought to be true without the evidence.

Koch discovered that methyl violet dye showed up the septicemia germ under a microscope by staining it. He also photographed the germs so that people outside of his laboratory could see them.

Koch also devised a method of proving which germ caused an infection. His work was rewarded in 1880 when he was appointed to a post at the Imperial Health Office in Berlin. Here, Koch perfected the technique of growing pure cultures of germs using a mix of potatoes and gelatin. This was a solid enough substance to allow for the germs to be studied better. Koch gathered round him a team of researchers in Berlin in 1881 and began to work on one of the worst diseases of the nineteenth century – tuberculosis (TB).

 

The TB germ was much smaller than the anthrax germ so the search for it was difficult. Using a more specialized version of his dye technique, Koch and his team searched for the TB germ. In May 1882, Koch announced that his team had found the germ. His announcement caused great excitement. It also generated what became known as ‘microbe hunters’ – a new generation of young scientists who were inspired by the work of both Koch and Pasteur. One of those who was inspired by Koch was Paul Ehrlich.

What was Koch’s legacy? He had finally laid to rest the belief that ‘bad air’ caused disease. He had inspired many other younger researchers to build on his work. He had found the germs of two feared diseases– anthrax and TB. He had developed research techniques that others could use throughout the world. By 1900, twenty-one germs that caused diseases had been identified in just 21 years. "As soon as the right method was found, discoveries came as easily as ripe apples from a tree." (Koch) It was Koch who had developed the right methods.

 

6.   Paul Ehrlich (1854 – 1915)

 

Paul Ehrlich was a German bacteriologist.

 Ehrlich was born on March 14, 1854, in Strehlen, Silesia (then part of Germany), to a prosperous Jewish family. He was the son of Ismar Ehrlich and his wife, Rosa, the aunt of bacteriologist Karl Weigert. Ehrlich's interest in biology and chemistry led him to study medicine. He attended universities in Breslau, Strasbourg, Frieberg-im-Briesgau, and Leipzig, earning his medical degree in 1878. Ehrlich was fascinated by the reactions of cells and tissues to dyes. Using aniline dyes, for example, Ehrlich investigated white blood cells. In the process, he developed new ways of staining cells for research, including the methylene blue stain for bacteria. Heinrich Koch used this stain whenhe discovered the bacillus that causes tuberculosis.

In 1890, Ehrlich became a professor at the University of Berlin, where he worked with Emil von Behring and Shibasaburo Kitasato on the study of immunity or the body's own defense against disease. The group searched for a substance that would give immunity against diphtheria using antitoxins. Antitoxins are antibodies produced by the body's immune system to fight poisons invading the body. Ehrlich worked on the chemical aspects of the study and, in 1892, the group announced the development of a diphtheria antitoxin for medical use. Ehrlich also pioneered the production of large quantities of the antitoxin using horses. He shared the 1908 Nobel Prize in Physiology or Medicine with Soviet biologist Elie Metchnikoff (1845-1916) for his work on immunity and serum therapy.

In 1894, Ehrlich was made director of a new institute for serum research in Frankfurt, where he studied the concepts of active and passive immunity and developed his "side-chain" theory of immunity to explain how antitoxins work at the cellular level in response to toxins. Ehrlich also continued his study of blood using staining techniques. Realizing that stains colored bacteria but not surrounding cells, he looked for a way to combine the stain with a substance that could kill the bacteria. This, he reasoned, could be a "magic bullet" in the fight against bacterial diseases. He also identified dyes, such as trypan red that had the ability to destroy microorganisms on their own.

Ehrlich began working with organic compounds containing arsenic because he felt its properties were similar to those of the nitrogen atoms that gave trypan red its effectiveness. He studied literally hundreds of arsenic compounds and by 1907 he had reached number 606, which he put aside because it was not effective against trypanosomes. However, two years later Ehrlich's assistant, Sahachiro Hata (1872-1938), discovered that the compound number 606 was effective against the dread disease syphilis. Caused by a microorganism called a spirochete, syphilis meant a slow and painful death for thousands of people. In 1910, Ehrlich announced that chemical 606, which he called Salvarsan, could cure syphilis.

For several years, Ehrlich suffered personal and professional attacks because of his work with syphilis. Some felt the disease was a just punishment for sinful sexual behavior and attacked Ehrlich for searching for a cure. The administration of the drug was also complicated, even risky at first, and when a few patients died because doctors administering the drug failed to follow Ehrlich's instructions, Ehrlich was accused of fraud. The attacks finally ceased in 1914, when the German parliament at last endorsed his cure as authentic.

Ehrlich was married in 1883 to Hedwig Pinkus. The couple had two daughters. Unfortunately, the strain surrounding Ehrlich's controversial efforts to cure syphilis took its toll on his health and he suffered a series of strokes during his last year, which led to his death in Bad Homburg, Germany, in 1915.

 

7.   Alexander Fleming (1881 – 1955)

 

Fleming was a Scottish bacteriologist and Nobel Prize winner, best known for his discovery of penicillin.

Alexander Fleming was born in Ayrshire on 6 August 1881, the son of a farmer. He moved to London at the age of 13 and later trained as a doctor. He qualified with distinction in 1906 and began research at St Mary's Hospital Medical School at the University of London under Sir Almroth Wright, a pioneer in vaccine therapy. In World War One Fleming served in the Army Medical Corps and was mentioned in dispatches. After the war, he returned to St Mary's.

In 1928, while studying influenza, Fleming noticed that mould had developed accidentally on a set of culture dishes being used to grow the staphylococci germ. The mould had created a bacteria-free circle around itself. Fleming experimented further and named the active substance penicillin. It was two other scientists however, Australian Howard Florey and Ernst Chain, a refugee from Nazi Germany, who developed penicillin further so that it could be produced as a drug. At first supplies of penicillin were very limited but by the 1940s it was being mass-produced by the American drugs industry.

Fleming wrote numerous papers on bacteriology, immunology and chemotherapy. He was elected professor of the medical school in 1928 and emeritus professor of bacteriology at the University of London in 1948. He was elected fellow of the Royal Society in 1943 and knighted in 1944. In 1945 Fleming, Florey and Chain shared the Nobel Prize in Medicine. Fleming died on 11 March 1955.