Microbiology is a science that deals with the study of living organisms and agents that are too small to be seen clearly by the naked eye. Greek – ‘Mikros’ means small, ‘Bios‘ means life and ‘Logos’ means science.

Development of Microscope In 1590, Zacharias Janssen, developed a prototype of the present day telescope and the compound microscope. Galileo also constructed a microscope Anton Van Leeuwenhoek (1632 – 1723) constructed simple microscope could magnify up to 300 times His descriptions of animalcules were made from Robert Hooke (1665) compound microscope

Robert Hooke’s compound microscope

Theory of Spontaneous generation Italian physician Francesco Redi disproved this theory in 1688 (Maggots over meat) Italian Priest and naturalist Lazzaro Spallanzani (1729 – 1799) (Microbes not found in heated broth) Louis Pasteur (1822 – 1895), a French Chemist John Tyndall (1820 – 1893), English Physicist. swan-neck-flask experiment of Louis Pasteur in 1861 conclusively disproved the theory of spontaneous generation

Francesco Reddi

Spallanzani ‘s work Spallanzani put broth into four flasks Flask 1 was left open - Microbes found Flask 2 was sealed - Microbes found Flask 3 was boiled and then left open -Microbes found Flask 4 was boiled and then sealed- Microbes not found

Pasteur’s Swan neck flask

Germ theory of Disease Agostino Bassi, in 1835 was the first demonstrate that microorganism cause disease 1867, Joseph Lister, introduced antibiotic principles carbolic acid as antiseptic Robert Koch - His criteria for providing casual relationship between a microorganism and a specific disease are known as Koch’s postulates

Koch’s postulates The microorganism must be present in very case of the disease but absent from healthy host The suspected microorganism must be isolated and grown in a pure culture The same disease must result when the isolated microorganism is inoculated into a healthy host The same microorganism must be isolated again from the experimentally diseased host

Other contributions of Koch Robert Koch also developed techniques to grow bacteria on solid media On sterile surfaces of cut, boiled potatoes Gelatin to solidify liquid medium Fannie Eilshemius Hesse suggested the use of agar as a solidifying agent Agar is not digested by most bacteria Agar remains solid until temperature reaches above 98 o C and medium solidifies at around 44 o C Richard Petri developed the Petridish for cultivation of bacteria

Robert Koch

Vaccination was successfully used against smallpox by Edward Jenner Elie Metchnikoff discovered some blood leucocytes that could engulf disease causing bacteria Phagocytes, phagocytosis Winogradsky, Beijerinck ecological role of microorganisms role of microorganisms in carbon, nitrogen and sulfur cycles enrichment – culture technique

Other significant developments in microbiology 1796 – Edward Jenner – Vaccination – Smallpox 1873 – John Lister - obtained pure culture of bacteria by serial dilution 1881 – Paul Ehrlich - Staining of bacteria with methylene blue 1881 – 1883 – Robert Koch – Simple methods for isolation and maintenance of microorganisms on chemically defined solid medium 1884 – Hans Christian Gram – differential staining

1884 – Elie Metchnikoff – Phagocytosis – WBC engulfing foreign particles 1884 – Charle Chamberland – Invention of bacterial filters for sterilization of liquids. Invention of autoclave 1892 – Iwanowski – observed filterable particles (virus) 1929 – Alexander Fleming – Antibiotics - penicillin 1860 to Golden Age of Microbiology.

Grouping and Description of living organisms Prokaryotic cells lack a true membrane – delimited nucleus; All bacteria Eukaryotic cells Cells that have a membrane enclosed nucleus

Description of Microorganisms Bacteria prokaryotes, unicellular organisms binary fission. Size 0.1 µ m to 18 µ m Viruses infectious agents having a simple organization protein coat single type nucleic acid (either RNA / DNA), Size ranges from 20 to 350 nm Fungi eukaryotic, spore-bearing organisms absorptive nutrition

Algae Algae are eukaryotic lack roots and leaves have chlorophyll Protozoa eucaryotic protist, not multicellular

Classification of Living organisms All organisms were earlier classified into two groups Plants and animals third kingdom called Protista, Haeckel (1866) consisting of unicellular organisms Copeland (1956) created a fourth kingdom Monera, unicellular prokaryotic bacteria fifth kingdom Mycetae created by Whittaker (1969) accommodate fungi

Robert H. Whittaker in 1969, placed organisms into five kingdom based on three major criteria Cell type (Procaryotic / Eucaryotic) Level of organization (Solitary / colonial; Uni or multicellular) Nutritional type  Kingdom : Monera or Procaryote All procaryotes  Kingdom : Protista

Unicellular or colonical eucaryotic organisms that lack Protozoa, lower fungi and smaller algae  Kingdom : Fungi  Kingdom : Animalia Multicellular animals with ingestive nutrition  Kingdom : Plantae Multicellular plants with walled eucaryotic cells and photosynthesis

Cavalier – Smith’s classification Empire : Bacteria Kingdom – Eubacteria Arahaebacteria Empire : Eucaryota Kingdom - Archaozoa Protozoa Chromista Plantae Fungi Animalia

Carl Woese comparison of RNA sequences, developed a three domain or empire classification Eubacteria, Archaebacteria, Eucaryotes, which are placed above kingdom level. bacterial classification on the basis of similarities Bergey’s Manual of Systematic Bacteriology (1984) prokaryotes are grouped on basis of characteristics Gram stain, morphology motility, structural features distinguishing physiological features

Nowadays organisms are grouped on a genetic basis nucleotide sequences of the small subunit ribosomal RNA (rRNA) C. Woese developed the phylogenetic tree of prokaryotes 16S rRNA of 30S ribosomes yield highly conserved sequences