Introduction to Microbiology Dr oruba Medical microbiology is

Introduction to Microbiology Dr. oruba

�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 Yeast: a singlecelled fungi �Yeasts �Single-celled �Superficial infections �Reproduce by budding �Athlete’s foot �Molds �Ringworm �Large, fuzzy, multicelled �Thrush organisms �Produce spores �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