Prokaryotes and Eukaryotes | CHAPTER 1 | Microbiology & Parasitology for Nurses

Prokaryotes and Eukaryotes – Basic microbiology, parasitology, and immunology; nature, reproduction, growth, and transmission of common microorganisms and parasites in Bangladesh; prevention including universal precaution and immunization, control, sterilization, and disinfection; and specimen collections and examination. Students will have an understanding of common organisms and parasites caused human diseases and acquire knowledge about the prevention and control of those organisms.

Prokaryotes and Eukaryotes

Definition of Prokaryotes;

‘Pro’ means primitive & ‘karyotes’ means nucleus. So, literally prokaryotes mean the cells having a primitive nucleus.
Prokaryotes are cells having a primitive nucleus or nucleoid consisting of a single molecule of loosely organized DNA lacking nuclear membrane, nucleolus, nucleoplasm and mitotic apparatus.

Example: All and only bacteria.

Features of Prokaryotes;

• Cells have no nucleus but nucleoid.
• Lacking nuclear membrane, nucleoplasm and mitotic apparatus.
• Single circular chromosome.
• No membrane bound organelles.
• 70S (50S + 30S) ribosome.
• Reproduce asexually or by binary fission.
• Cell wall has peptidoglycan

Definition of Eukaryotes;

Eu’ means normal & ‘karyotes’ means nucleus. So, literally eukaryotes means the cells having a normal nucleus.

Eukaryotes are cells having a true nucleus with multiple chromosomes, nucleolus & nucleoplasm surrounded by a nuclear membrane and using mitotic apparatus for their division.

Example: Human cells, protozoa, fungi, plant cells etc.

Features of Eukaryotes;

• Cells have organized nucleus with DNA, nuclear membrane, nucleolus & nucleoplasm.
  Many linear chromosomes.
• Membrane bound organelles present.
• 80S (60S+40S) ribosome.
• Reproduce sexually or asexually.
• Cell may or may not have cell walls. If cell wall is present, it is made up of cellulose or chitin.

Differences between Prokaryotic (Bacteria) & Eukaryotic (Human) Cell;

History of Microbiology

Microbiology has had a long, rich history, initially centered in the causes of infectious diseases but now including practical applications of the science. Many individuals have made significant contributions to the development of microbiology.

Early history of microbiology: Historians are unsure who made the first observations of microorganisms, but the microscope was available during the mid-1600s, and an English scientist named Robert Hooke made key observations. He is reputed to have observed strands of fungi among the specimens of cells he viewed. In the 1670s and the decades thereafter, a Dutch merchant named Anton van Leeuwenhoek made careful observations of microscopic organisms, which he called animalcules.

Until his death in 1723, van Leeuwenhoek revealed the microscopic world to scientists of the day and is regarded as one of the first to provide accurate descriptions of protozoa, fungi, and bacteria.

After van Leeuwenhoek died, the study of microbiology did not develop rapidly because microscopes were rare and the interest in microorganisms was not high. In those years, scientists. debated the theory of spontaneous generation, which stated that microorganisms arise from lifeless matter such as beef broth.

This theory was disputed by Francesco Redi, who showed that fly maggots do not arise from decaying meat (as others believed) if the meat is covered to prevent the entry of flies. An English cleric named John Needham advanced spontaneous generation, but Lazzaro Spallanzani disputed the theory by showing that boiled broth would not give rise to microscopic forms of life.

Louis Pasteur and the germ theory: Louis Pasteur worked in the middle and late 1800s. He performed numerous experiments to discover why wine and dairy products became sour, and he found that bacteria were to blame. Pasteur called attention to the importance of microorganisms in everyday life and stirred scientists to think that if bacteria could make the wine “sick,” then perhaps they could cause human illness.

Pasteur had to disprove spontaneous generation to sustain his theory, and he therefore devised a series of swan-necked flasks filled with broth. He left the flasks of broth open to the air, but the flasks had a curve in the neck so that microorganisms would fall into the neck, not the broth.

The flasks did not become contaminated (as he predicted they would not), and Pasteur’s experiments put to rest the notion of spontaneous generation. His work also encouraged the belief that microorganisms were in the air and could cause disease. Pasteur postulated the germ theory of disease, which states that microorganisms are the causes of infectious disease.

Pasteur’s attempts to prove the germ theory were unsuccessful. However, the German scientist Robert Koch provided the proof by cultivating anthrax bacteria apart from any other type of organism. He then injected pure cultures of the bacilli into mice and showed that the bacilli invariably caused anthrax. The procedures used by Koch came to be known as Koch’s M postulates They provided a set of principles whereby other microorganisms could be related to ud other diseases.

The development of microbiology: In the late 1800s and for the first decade of the 1900s, scientists seized the opportunity to further develop the germ theory of disease as enunciated by m Pasteur and proved by Koch. There emerged a Golden Age of Microbiology during which many agents of different infectious diseases were identified. Many of the etiologic agents of microbial disease were discovered during that period, leading to the ability to halt epidemics by m interrupting the spread of microorganisms,

Despite the advances in microbiology, it was rarely possible to render life-saving therapy to an infected patient. Then, after World War II, the antibiotics were introduced to medicine. The incidence of pneumonia, tuberculosis, meningitis, syphilis, and many other diseases declined with the use of antibiotics.

Work with viruses could not be effectively performed until instruments were developed to help scientists see these disease agents. In the 1940s, the electron microscope was developed and perfected. In that decade, cultivation methods for viruses were also introduced, and the knowledge of viruses developed rapidly. With the development of vaccines in the 1950s and 1960s, such viral diseases as polio, measles, mumps, and rubella came under control.

Modern microbiology: Modern microbiology reaches into many fields of human endeavor, including the development of pharmaceutical products, the use of quality-control methods in food and dairy product production, the control of disease-causing microorganisms in consumable waters, and the industrial applications of microorganisms.

Microorganisms are used to produce vitamins, amino acids, enzymes, and growth supplements. They manufacture many foods, including fermented dairy products (sour cream, yogurt, and buttermilk), as well as other fermented foods such as pickles, sauerkraut, breads, and alcoholic beverages.

One of the major areas of applied microbiology is biotechnology. In this discipline, microorganisms are used as living factories to produce pharmaceuticals that otherwise could not be manufactured. These substances include the human hormone insulin, the antiviral substance interferon, numerous blood-clotting factors and clot dissolving enzymes, and a number of vaccines. Bacteria can be reengineered to increase plant resistance to insects and frost, and biotechnology will represent a major application of microorganisms in the next century.

The development of microbiology: In the late 1800s and for the first decade of the 1900s, scientists seized the opportunity to further develop the germ theory of disease as enunciated by Pasteur and proved by Koch. There emerged a Golden Age of Microbiology during which many agents of different infectious diseases were identified. Many of the etiologic agents of microbial disease were discovered during that period, leading to the ability to halt epidemics by interrupting the spread of microorganisms.

Despite the advances in microbiology, it was rarely possible to render life-saving therapy to an infected patient. Then, after World War II, the antibiotics were introduced to medicine: The incidence of pneumonia, tuberculosis, meningitis, syphilis, and many other diseases declined with the use of antibiotics.

Work with viruses could not be effectively performed until instruments were developed to help scientists see these disease agents. In the 1940s, the electron microscope was developed and perfected. In that decade, cultivation methods for viruses were also introduced, and the knowledge of viruses developed rapidly. With the development of vaccines in the 1950s and 1960s, such viral diseases as polio, measles, mumps, and rubella came under control.

Robert Koch

Robert Heinrich Hermann Koch (11 December 1843 – 27 May 1910) was a German physician and microbiologist. As the founder of modern bacteriology, he identified the specific causative agents of tuberculosis, cholera, and anthrax and gave experimental support for the concept of infectious disease, which included experiments on humans. Koch created and improved laboratory technologies and techniques in the field of microbiology, and made key discoveries in public health.

His research led to the creation of Koch’s postulates, a series of four generalized principles linking specific microorganisms to specific diseases that remain today the “gold standard” in medical microbiology. For his research on tuberculosis, Koch received the Nobel Prize in Physiology or Medicine in 1905. The Robert Koch Institute is named in his honor.

Born –

• Robert Heinrich Hermann Koch
• 11 December 1843
• Clausthal, Kingdom of Hanover

Died –

• 27 May 1910 (aged 66)
• Baden-Baden, Grand Duchy of Baden

Nationality –

• German

Alma mater –

• University of Göttingen

Known for –

• Discovery bacteriology
• Koch’s postulates of germ theory
• Isolation of anthrax, tuberculosis and cholera

Awards –

• ForMemRS (1897)
• Nobel Prize in Medicine (1905)

Scientific career

Fields –

• Microbiology

Institutions –

• Imperial Health Office, Berlin, University of Berlin

Doctoral advisor –

• Georg Meissner

Other advisors –

• Friedrich Gustav Jakob Henle
• Karl Ewald Hasse
• Rudolf Virchow

Influenced –

• Friedrich Loeffler

Koch’s Postulates:

Robert Koch, Father of modem microbiology announced his discovery of V. cholerae in Berlin conference in 1884. The famous postulates were also published at that time. Koch’s postulate establishes the aetiological relationship between an organism and a particular disease.

Components: The postulates were 4 in number –

• The organism should be constantly associated with the disease and should be always found in the diseased and not in healthy ones.
• The organism should be isolated in pure culture from the lesion.
• When cultured agent die is introduced to a healthy person / animal, the same disease must occur.
• The same organism must be isolated again from the inoculated animal.

Limitations/ diseases do not fulfill the Koch’s postulates:

• Genetic, auto-immune and non-culturable microbial diseases. Because, in these cases causative agents cannot be identified.
• Some microbes cannot be cultured in artificial media, e.g. – Treponema pallidum, Mycobacterium leprae etc.
• Some microbes cannot produce disease in experimental animals, e.g. – Neisseria gonorrhoeae.
• Some diseases may be caused by mixed infection with more than one microbe.

Comparison of Medically Important Organisms;

Figure: Bacterial cell, Virus, Fungus

Figure: Protozoa

Emerging Diseases;

An emerging disease is one that has appeared in a population for the first time, or that may have existed previously but is rapidly increasing in incidence or geographic range.

Example: AIDS, Ebola.

Re-Emerging Diseases:

Re-emerging disease are age-old diseases that have increased its prevalence again. These diseases were previously treatable but have developed resistance to the drugs used to treat them. The increased in migration due to war and international travel has also facilitated the spread of disease.

Example of Re-Emerging Diseases:

• Tuberculosis.
• Cholera.
• Malaria.
• Kala-azar.

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