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The study of microorganisms. The science which treats the nature, life and action of microorganisms.


The state of being soiled or infected by contact with infectious organisms or other material


A unit of measurement; 1/1000 of a millimeter or 1/25,000 of an inch; usually designated by the Greek letter "u".


Describes all living materials in a cell. A thick mucous-like substance that is colorless and translucent that forms the biochemical basis of life within the cell nucleus.

Components of a cell

cell wall, cell membrane, cytoplasm, capsule, flagella, nucleus


The process by which some cells can ingest bacteria or other foreign particles. (process where white blood cells in the human body destroy bacteria by engulfing them).


The living matter of a cell between the cell's membrane and nucleus.


The functional center of a cell that governs activity and heredity.


Deoxyribonucleic Acid. The protein found in the chromosomes of a cell nucleus which is the basis of heredity..

Cell wall

A tough rigid structure that helps maintain the cell's shape.

Cell membrane

This layer is located just beneath the cell wall which is semi-permeable.


A mucus material that protects the bacteria from the host cells that try to destroy it.


Thread-like tails attached to the cell that enable the bacteria to move through liquids.

Acid-fast bacteria

Mycobacterium tuberculosis (which causes tuberculosis) and Mycobacterium leprae (which cause leprosy).


Microrganisms capable of forming a thick wall around themselves enabling them to survive in adverse conditions; a resistant form of bacterium.


A molecule in plants that absorbs sunlight, and converts it to energy in a process called photosynthesis.

Aerobic bacteria

Capable of growing in the presence of free oxygen. Requiring oxygen.

Anaerobic bacteria

Capable of growing in the absence of free oxygen. Not requiring oxygen.

Psychrophiles (bacteria)

Cold-loving bacteria (59-68 degrees F)

Mseophiles (bacteria)

Bacteria that grows best at moderate temperatures (68-113 degrees F)

Thermophiles (bacteria)

Bacteria which grow best at a temperatures (122-158 degrees F).

Vegetative stage

State of active growth of microorganisms (as apposed to the resting or spore stages)


A unit that measure visible light.

Binary fission

The typical method of bacterial reproduction in which a cell divides into equal parts.

Methicillin-Resistant Staphylococcus Aureus (MRSA)

Staphylococcus aureus bacteria that have developed a resistance to Methicillin, the drug of choice.

Vancomycin-Resistant Enterococcus (VRE)

Enterococcus bacteria that are no longer sensitive to Vancomycin.


One of a group of minute infections agents that grow only in living tissues or cells.


The animal, plant, or human that supports the growth of microorganisms.


Any one-celled animal-like microorganism of the sub-kingdom protozoa.

Amoeboid movement

The crawling movement of cells brought about by the cell successively becoming longer and then retracting.


A large group of plant-like organisms including molds, mushrooms, and yeasts without chlorophyll.

Causative agent (chain of infection)

The microorganism that causes an infectious disease.

Reservoir of agent (chain of infection)

The place where an infectious agent (microorganism) can survive.


An individual who harbors and disseminates specific pathogenic microorganisms without manifesting any clinical symptoms, and who serves as an intermediary in the transfer of diseases to a susceptible person.

Portal of exit (chain of infection)

The path by which an infectious agent leaves the reservoir.

Mode of transmission (chain of infection)

The method of transfer of an infectious agent from the reservoir to a susceptible host.

Portal of entry (chain of infection)

The path used by an infectious agent to enter a susceptible host.

Susceptible host (chain of infection)

A person or animal that lacks the ability to resist infection by an infectious agent.

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