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Principles of Medical Biology - Microbial Diseases Flashcards

The Biology of Microbial Diseases

Microbiology

  • Microbiology is the study of microorganisms.

  • Microorganisms are very small and cannot be seen with the naked eye; a microscope is required.

  • Micro = very small or microscopic.

  • Microorganisms are commonly referred to as “germs” or “microbes”.

  • Microbes include bacteria, viruses, fungi, algae, protozoa, and helminths.

Branches of Microbiology

  • Bacteriology: Studying bacteria.

  • Mycology: Studying fungi and yeast.

  • Virology: Studying viruses.

  • Parasitology: Studying parasitic protozoans and helminths.

Microorganisms or Microbes

  • Small living organisms.

  • Not visible to the naked eye.

  • Microscope must be used to see them.

  • Found everywhere in the environment.

  • Found on and in the human body.

  • Many are part of the normal flora of the body.

  • May be beneficial.

  • Called nonpathogens when not harmful to the body.

  • Some cause infections and diseases.

  • Called pathogens (germs) when able to harm the body.

  • Most prefer warm environments.

  • Most prefer darkness.

  • Need a source of food and moisture.

  • The need for oxygen varies.

  • The human body is an ideal supplier of all the requirements.

Antibiotics

  • Antibiotics are used to kill bacteria.

  • Some strains of bacteria have become antibiotic-resistant.

  • When antibiotic-resistant, the antibiotic is no longer effective against the bacteria.

Protozoa

  • One-celled, animal-like organism.

  • Found in decayed materials and contaminated water.

  • May have flagella for movement.

  • Some are pathogenic.

Fungi

  • Simple, plant-like organisms.

  • Live on dead organic matter.

  • Yeast and molds.

  • Can be pathogenic.

  • Antibiotics do not kill fungi.

  • Antifungal medications are required.

Rickettsiae

  • Parasitic microorganisms.

  • Cannot live outside the cells of another living organism.

  • Transmitted to humans by the bites of insects (e.g., fleas, lice, ticks, mites).

  • Antibiotics are effective against many of them.

Viruses

  • Smallest microorganisms.

  • Must use an electron microscope to see them.

  • Must be inside another living cell to reproduce.

  • Spread by blood and body secretions.

  • Very difficult to kill.

  • Cause many diseases.

  • Viruses infecting animals can mutate to infect humans.

  • Examples include:

    • Severe acute respiratory syndrome (SARS)

    • Ebola and Marburg

    • H5N1

Virus—Hepatitis B

  • Also called serum hepatitis.

  • Caused by HBV.

  • Transmitted by blood serum and body secretions.

  • Affects the liver.

  • A vaccine is available for protection.

  • The vaccine is expensive.

  • The vaccine is given in a series of three injections.

  • By law, employers must provide the vaccine at no cost to employees with occupational exposure to blood or other body secretions.

  • If an employee refuses, a written statement must be signed documenting the refusal.

Hepatitis C

  • Caused by HCV.

  • Transmitted by blood and blood-containing body fluids.

  • Many infected individuals are asymptomatic.

  • Others have mild symptoms.

  • Can cause severe liver damage.

  • Currently, no vaccine is ready for use.

  • A vaccine is in the development stage.

  • Extremely difficult to destroy HCV.

  • Can survive and remain active for several days in dried blood.

  • Health care workers must follow precautions to protect against the virus.

Acquired Immune Deficiency Syndrome (AIDS)

  • Caused by the Human Immunodeficiency Virus (HIV).

  • Suppresses the immune system.

  • The individual becomes susceptible to cancers and infections that would not affect a healthy person.

  • No cure presently and no vaccine.

  • Take precautions for prevention.

Helminths

  • Multicellular parasites, otherwise known as worms or flukes.

  • Are transmitted:

    • By eating contaminated food

    • Being bitten by infected insects

    • When worms enter the skin

How Pathogens Cause Infection and Disease

  • Some cause an allergic reaction.

  • Some produce poisons called toxins.

  • Others attach and destroy the living cells they invade.

Chain of Infection

  • Present for disease to occur and spread from one individual to another.

    • Causative agent

    • Reservoir

    • Portal of exit

    • Mode of transmission

    • Portal of entry

    • Susceptible host

Common Body Defenses

  • Mucous membranes

  • Cilia

  • Coughing and sneezing

  • HCl in the stomach

  • Tears

  • Fever

  • Inflammation response

  • Immune response

Ending the Chain of Infection

  • Eliminate any step in the chain, and infection is stopped.

  • Follow practices to interrupt or break the chain.

  • Remember, pathogens are everywhere.

  • Prevention is a continuous process.

General Characters of Bacteria

  • Bacteria are prokaryotic unicellular organisms.

  • Play an important role in different areas of life, in food, industry, medicine, economy.

  • These organisms have a cell wall structure and possess one chromosome, some contain an extra-chromosomal circular DNA called plasmids, which play important roles in resistance to antibiotics.

  • Depending on oxygen requirement, they can be classified into:

    • Anaerobes (able to live in the absence of O_2)

    • Aerobes (require O_2 to stay alive).

  • Depending on nutritional requirement, they can be:

    • Heterotrophs (depends on an external source for obtaining energy)

    • Autotrophs (they can make their food and provide an energy source).

Bacteria

  • Simple, one-celled organisms.

  • Multiply rapidly.

  • Classified by shape and arrangement.

  • Cocci are round or spherical in shape.

    • Diplococci—in pairs.

    • Streptococci—in chains.

    • Staphylococci—clusters or groups.

  • Bacilli are rod-shaped.

    • Occur singly, in pairs, or in chains.

    • May have flagella.

    • Ability to form spores.

  • Spirilla are spiral or corkscrew-shaped.

    • Includes comma-shaped vibrio and corkscrew spirochete.

    • Diseases include syphilis and cholera.

Gram Stain

  • It is a type of stain and the first step in bacterial identification.

  • Through which bacteria can be divided into two main groups:

    1. Gram-positive: Bacteria stained purple.

      • They have a thick cell wall (peptidoglycan) and (teichoic acid).

    2. Gram-negative: Bacteria stained pink.

      • They have a thin cell wall (peptidoglycan) and (lipopolysaccharides) with no (teichoic acid).

The Gram Stain Has Four Steps:

  1. Crystal violet, the primary stain, followed by

  2. Iodine, which acts as a mordant by forming a crystal violet-iodine complex, then

  3. Alcohol, which decolorizes, followed by

  4. Safranin, the counterstain.

Culture media

  • Culture medium: It is a specific nutritional medium that supports the growth of microorganisms by providing the requirements for growth due to its ingredients.

  • Agar: It is a complex polysaccharide that is used as a solidifying agent for culture media in Petri plates, slants,…. This agent is not metabolized by microbes (Liquefies at 100°C and solidifies ~40°C).

Culture Media Composition

  • Chemically defined media: Exact chemical composition is known.

  • Complex media: Extracts and digests of yeasts, meat, or plants. Moreover, the medium may be liquid like nutrient broth or solid like nutrient agar.

Types of Culture Media

  1. Basic medium: The medium supports the growth of nearly all types of bacteria due to its components, which support the growth of all types of bacteria.

  2. Selective medium: A type of bacteriologic medium prevents the growth of unwanted microbes by containing specific inhibitors like salt and antibiotics.

  3. Differential medium: A type of medium that enables us to distinguish related bacteria or colonies easily.

  4. Enrich medium: A type of medium that encourages the growth of a desired microbe rather than others.