Scope & history of Microbiology

Chapter 1Black, J.G.. Microbiology: principles and

explorations, latest edition.

• Microbiology: Study of microbes (microorganisms), they are so small that need microscope to study them.

• Where are they?• Air, water (oceans, springs, drinking water), soil, in & on human body, in

the deep hot interior of Earth (temp reaching 110C), Antarctic,

• Advantages- some capture energy & store it in molecules that other organisms used

as food source.- Some m.o decompose dead organism or waste material- They make N2 to plants- Certain m.o live in digestive system of grazing animals & serve in

digestive process- Biochemical rxns carried out by m.o are used by food industry to make

pickles, yogurt, - Fermentation rxns are used to make beer, wine, dough- One of the most important is synthesis of antibiotics- Vaccines for disease control- Considered major tool for genetic engineering (production of interferon,

growth hormone, insulin)

– Provides insight into life processes in all life forms: Ecology: based on microbiology principles we understand how matter decomposes & made available for recycling; biochemistry: use microbes to study metabolic pathways-sequence of chemical rxns in living organism; genetics: use microbes to study how hereditary information is transferred & how it controls the structure & function of organisms

• Microbes include: • Bacteria: Majority are single celled with spherical , rod, spiral shapes,

few are filamentous. Most of them absorb nutrient from environment, some make their nutrient by photosynthesis or other route. Widely distributed in environment & decaying matter, some cause diseases.

• Algae: many of them are single celled microscopic organism, some are large complex multicellular. They capture energy from light & are a source of food for other organisms

• Fungi: yeast & some molds are single celled m.o, mushrooms are multicellular. All fungi absorb ready made nutrients. Fungi are distributed in water & soil & decomposing dead organism, some cause diseases, others produce antibiotics.

• Viruses: acellular entities not seen by light microscope. Composed of nucleic acids & few proteins. They replicate when they invade cells. Many viruses can invade human cells & cause disease

• Viroid: smaller acellular agents of disease composed of nucleic acid without a protein coating. They cause plant diseases.

• Prions: Protein without any nucleic acid cause mad cow disease.

• Protozoa: single celled microscopic m.o (although few amoeba can be seen by naked eye, but need microscope to study them) with at least one nucleus & numerous intracellular structures. They gain food by engulfing or ingesting small m.o. They are found in soil, water & animals

• Helminths (worms): have microscopic stage in life cycle; arthropods (insects) can transmit microbes & cause diseases

• History

• Robert hooke (1665): built the compound microscope. Used the term "cell".

• Leeuwenhoek: used lenses to observe living m.o (magnification of 300x), he observed all kinds of m.o, protozoa, algae, yeast, fungi & bacteria in spherical, rod, spiral forms (tested samples from his teeth).

• The germ theory of disease• Spontaneous generation: spoilage of food, presence of

maggots in rotting meat arose from non living things, eg rodents arose from mist grains, beetles from dust, worms & frogs from mud!!

• Francisco Redi (late 17th century): did experiment to refute spontaneous generation (Meat & open/closed jar)

• Another scientist: boil broth, close it, no spoilage…….critics: loss of O2 inhibited growth!

• Several trials to introduce air…. All where criticised!

• 19th century: a competition to defeat the theory:

• Louis Pasteur: Boiled broth infusion in Swan-necked flask

• Tyndal (British): sealed flasks of boiled infusion in air tight box, dust settles down, remove the caps carefully.

• What if m.o withstand boiling???

• Pasteur's contribution:• Carefully selected yeast good wine, mix with other m.o sour taste

or oily taste he developed pasteurization (heating at 56C in absence of O2 for 30min)

• Developed vaccines for rabies

• Koch's contribution (Germany): • *Identified the bacteria that causes anthrax in dividing form & spore form• *Found ways to grow bacteria in pure culture. Used gelatine (problem:

melts at body temp –incubator temp- & microbes liquefies it).• * Tuberculin development (later used for detection of TB)• Angeline Hesse: suggested agar to grow microbe as thin layers &

isolate it.

• Koch's postulate to associate a particular organism with disease (Germ Theory of Disease):

1. The specific causative agent must be found in every case of the disease2. The disease organism must be isolated in pure culture

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3. inoculation of a sample of the culture into a healthy susceptible animal must produce the same disease

4. the disease organism must be recovered from the inoculated animal

• Koch identified the bacteria that causes tuberculosis & developed methods for its staining.

• Semmelweis (19th century-Austria): sanitary practice & hygiene (women in labour puerperal (childbed) fever)…..he was sent to asylum!!

• Lister: initiated the use of dilute carbolic acid (phenol) on bandages & instruments to reduce infection. The first 'aseptic technique' reduced surgical wound infection & considered the father of antiseptic surgery.

• Immunology• Disease depends not only on m.o but also on host's response

(response of immune system)• Ancient Chinese: scabs from recovering smallpox patient

ground into powder inhaled mild disease & protected from serious infection

• Edward Jenner: Observed that milkmaids who got cowpox didn't get smallpox. Fluid from cowpox blisterinoculated into 8yr old boy inoculated with smallpox

remained healthy child vaccinia (vacca=cow)

• Metchinkoff (Russian): scientists believed that immunity is due to non cellular substances in blood, he discovered that certain cells in the body ingest microbes, he named them phagocytes 'cell eating', he developed some vaccines, some were successful others failed.

• Virology: • emerged after bacteriology due to size of viruses• Pasteur's collaborator developed porcelain filter to remove

bacteria from water….virus?? The filtrate remains infectious due to pathogenic molecule i.e virus

• Chemotherapy:• Cinchona tree bark was used to treat malaria (quinine)

• Paul Ehrlich (German): certain dyes stain m.o but not animal cells, he searched for "magic bullet" a chemical that would destroy specific bacteria but not surrounding tissues,

• he discovered salvarsan (against syphilis)• used the term chemotherapy

• Fleming (Scottish): observed that a colony of penicillin mold contaminating a culture of Staphylococcus had prevented the growth of bacteria, (this was the discovery of antibiotics).

• Sulfa drugs were developed & used in treating streptococcal infections, later isoniazid was developed & still used today.

• Many antibiotics are produced from soil bacteria e.g streptomycin.

• Tomorrow's history:• Most of the development in genetics is due to studying microbes.

Scientists converted bacteria to factories that produce drugs, hormones, vaccines & biologically important compounds.

• Bacteriophages: viruses that attack & kill specific bacteria, were preferred in Soviet countries over the use of antibiotics.