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Introduction to Microbiology Dr. Waleed Khalid Saadoon Lec. : 1 Medical microbiology is the study of the causative agents of infectious diseases of humans and the reaction to such infections. In other words it deals with etiology, pathogenesis, laboratory diagnosis, specific treatment and control of infection (immunization). Medical microbiology includes: Bacteriology – The science that study bacteria, the causative agents of a number of infectious diseases. Virology – The science that study viruses, noncellular living systems, capable of causing infectious diseases in human being. Immunology – The science which concerned with mechanisms of body protection against pathogenic microorganisms and foreign cells and substances. Mycology – The science that deals with the study of fungi . Protozoology – It deals with pathogenic unicellular animal organisms. Classification of Microorganisms: Classification by structure Subcellular – DNA or RNA surrounded by a protein coat – viruses Prokaryotic – simple cell structure with no nucleus or organelles – bacteria Eukaryotic – complex cell structure with nucleus and specialized organelles – protozoa, fungi and parasites. Naming of Microorganisms: Standardized naming Genus Category of biologic classification Example – Staphylococcus Species of organism Represents a distinct type of microorganisms Examples – Staphylococcus aureus and Staphylococcus epidermidis The genus name is written with a capital letter, and the species name – with a small letter. How microorganisms cause disease? Microorganisms cause disease in a variety of ways 1- By using nutrients needed by cells and tissues 2-By damaging cells directly 3-By producing toxins Transmission Direct contact Indirect contact These microorganisms may remain localized or become systemic Localized symptoms Swelling Pain Warmth Redness Generalized symptoms Fever Tiredness Aches Weakness Normal flora Provides a barrier Can cause an infection when the immunity decrease . 1- Viruses They are the smallest known infectious agents They are subcellular microorganisms that : Have only nucleic acid surrounded by a protein coat Must live and grow in living cells of other organisms Hepatitis virus Illnesses caused by viruses Colds Influenza Hepatitis Warts AIDS Mumps Rubella Measles Herpes Vaccines are available for many viruses 2-Bacteria Single-celled prokaryotic organisms that reproduce rapidly . Classification Bacteria can be classified according to: 1- Shape 2- Ability to retain dyes 3- Ability to grow with / without air 4- Biochemical reactions Bacillus bacterial classification Classification and Identification 1- Shape Coccus – spherical, rounded, or ovoid Bacillus – rod-shaped Spirillum – spiral-shaped Virbrio – comma-shaped Spherical (cocci) bacteria 1. Micrococci 2. Diplococci 3. Streptococci 4. Tetracocci 5. Sarcine 6. Staphylococci Representatives of pathogenic cocci 1 2 1. Scanning Electron Micrograph of Streptococcus pneumoniae 2. Scanning Electron Micrograph of Staphylococcus aureus Electron Micrograph of Neisseria gonorrhoeae 2-Ability to retain certain dyes Gram’s stain Acid-fast stain 3- Ability to grow in presence or absence of air Aerobes – grow best in the presence of oxygen Anaerobes – grow best in the absence of oxygen 4- Biochemical reactions Special groups Mycobacteria – bacilli with a cell wall that differs from most bacteria Rickettsiae Very small Live and grow within other living organisms such as mites and ticks Chlamydiae Cell wall structure differs from other bacteria Live and grow within other living cells Mycoplasmas – Completely lack the rigid cell wall The size of bacteria The size of bacteria is measured in micrometer (m) or micron () (1 micron or micrometer is one thousandth of a millimeter) and varies from 0.1 to 16-18 . Most pathogenic bacteria measure from 0.1 to 10 . The other unit of measurement of microorganisms is nanometer (nm) (one millionth of a millimeter) . BACTERIAL CELL FLAGELLA Electron Micrograph of Bacteria with Flagella SPORE Bacillus anthracis Bacillus megaterium Cell wall In addition to conferring rigidity upon bacteria, the cell wall protects against osmotic damage Chemically, the rigid part of the cell wall is peptidoglycan Cell wall first described by Gram in 1884. It is used to study morphologic appearance of bacteria. Gram's stain differentiates all bacteria into two distinct groups: a. Gram-positive organisms b. Gram-negative organisms Gram Staining Technique 3- Protozoa Single-celled eukaryotic organisms, larger than bacteria, they are found in soil and water and they are a leading cause of death in developing countries Illnesses caused by protozoa are Malaria Amebic dysentery Trichomoniasis vaginitis Protozoan Trichomonas vaginalis 4- Fungi Eukaryotic organisms with rigid cell wall Yeasts Single-celled Reproduce by budding Molds Large, fuzzy, multicelled organisms Produce spores Yeast: a singlecelled fungi Superficial infections Athlete’s foot Ringworm Thrush Can cause systemic infections Multicellular Parasites Organisms that live on or in another organism and use it for nourishment Parasitic worms Usually due to poor sanitation Round worms Flat worms Tape worms Parasitic insects Bite or burrow under the skin Mosquitoes Ticks Lice Mites Apply Your Knowledge Matching: ANSWER: ___ D Yeast or mold A. Virus ___ E Tapeworm / lice B. Bacteria ___ B Classified by shape C. Protozoan ___ A Subcellular organism D. Fungus ___ B May be aerobic or anaerobic E. Multicellular parasite A Smallest known organism ___ C Found in soil and water ___ Very Good!
