Microbiology

I. What is a microorganism? A. Microorganisms are living things which are not visible without use of a microscope. ○ 1. Viruses, although not technically living due to the lack of cellular structure, are classed as a microorganism. Viruses are much smaller than bacteria, even small enough to infect bacteria cells. ○ 2. Bacteria from kingdoms Bacteria and Archaebactera are unicellular microorganisms.

I. What is a microorganism? 3. Some protists can be microorganisms. Examples include organisms that are plant-like protists (algae) and animal-like protists (protozoa). 4. Some unicellular fungus (such as yeast) are microorganisms. ○ B. Some microorganisms are beneficial to humans, but others are harmful. The term for disease-causing organisms is pathogenic (“pathogen” refers to a specific disease-causing organism). Most pathogens are considered parasites because they harm their host.

II. How does a virus make me sick? A. Viruses are composed of a protein coat (called a capsid) that protects a nucleic acid (may be either DNA or RNA). Viruses are not cellular because they lack a cell membrane, cytoplasm, and ribosomes. B. A virus can only exist by infecting a host cell. Viruses are classified by the reproductive cycle it uses to infect the host cell.

II. How does a virus make me sick? ○ 1. The lytic cycle describes the “life cycle” in which a virus quickly kills the host cell. a. The virus attaches to the host cell using the shape of the capsid. The shape of the capsid thus determines the types of cells a virus may infect. Most viruses are tissue and specie- specific (only able to infect certain cells of a certain specie). b. The virus then injects the nucleic acid from the capsid into the host cell. The capsid remains on the outside. c. The nucleic acid begins using the cell’s enzymes, ribosomes, and other structures to produce copies of the viral nucleic acid and capsid.

II. How does a virus make me sick? d. The copies are assembled within the cell. When enough copies accumulate, the cell ruptures like an overfilled balloon. The rupture of the cell (lysis) destroys the cell and can lead to damage of the host. e. The released copies then begin attaching to neighboring cells, or the viral particles are released by sneezing, coughing, etc and enter another host.

II. How does a virus make me sick?  2. The lysogenic cycle describes the “life cycle” in which the virus has a dormant (inactive) stage. This cycle follows all of the steps of the lytic cycle but includes a period in which the virus remains inactive within the cell. This dormant period may last for weeks, months, or years.

II. How does a virus make me sick? C. HIV, influenza, and smallpox are diseases caused by viruses that have killed millions of people.  1. HIV causes AIDS.  a. HIV is a retrovirus. This means that the virus injects RNA into the cell, along with a special enzyme. The special enzyme changes the RNA into DNA which can insert itself into the DNA of the host cell. b. HIV infects T-cells, which are important for the immune response. Thus, people with AIDS often die of opportunistic infections, such as pneumonia. c. HIV is transmitted through blood, vaginal secretions, semen, breast milk, and across the placenta.

II. How does a virus make me sick? ○ 2. Several different viruses cause influenza (the “flu”) a. The influenza viruses (as well as HIV and other viruses) mutate rapidly. The effect of these mutations (changes in DNA) is that the actual virus being spread throughout the population changes with each outbreak. Flu epidemics are caused by viruses that are genetically different enough from earlier years’ viruses that people have little immunity to them. b. Influenza viruses infect respiratory cells (cells that line your throat and lungs). The lysis of these cells leads to some of the typical symptoms of the flu, such as sore throat and congestion.

II. How does a virus make me sick?  c. Influenza is transmitted through droplets of affected bodily fluids, such as saliva and mucus. The virus survives long enough outside the host organism that droplets left on surfaces (such as a desk) contain viable viral particles for several hours.

II. How does a virus make me sick? ○ 3. A poxvirus causes smallpox. a. The smallpox disease has been eradicated by a special coordination of epidemiologists, doctors, and politicians around the world. However, samples of the smallpox virus were kept for study. Currently, these samples (the demon in the freezer) are stored at the CDC in Atlanta and a similar organization in Russia. b. Smallpox initially infects the cells of the lymph nodes and lungs. Within a week, the virus moves into the liver, spleen, other internal organs and the skin. Lesions form one week after exposure and last approximately one month. Symptoms include severe headaches, muscle ache, and pustules on the skin.

II. How does a virus make me sick?  c. Smallpox is transmitted by droplets exhaled by infected people. Virus can survive prolonged periods of time in dust, clothing, bedding and other objects.

Review Questions:  1. Name four microorganisms.  Virus, Bacteria, Protist, and Fungus  2. What is a pathogen?  A disease causing organism  3. What are the two parts of a virus?  Protein coat and Nucleic Acid  4. What are the two reproductive cycles of viruses?  Lytic Cycle and Lysogenic  5. What type of cell does HIV infect?  T-Cells  6. Why is there a different flu virus each year?  It mutates rapidly  7. How is smallpox transmitted?  Droplets exhaled by infected people

III. Are all sicknesses caused by a virus?  A. Although most bacteria are beneficial, many diseases are caused by pathogenic bacteria. One example is the streptococcus bacteria, causing more illnesses than any other bacteria. Streptococcus causes scarlet fever, “strep throat” and a form of pneumonia. Streptococcus causes disease because it destroys cells. The cells are broken down by the bacteria as a source of food/nutrition. Other bacteria harm the host by releasing toxins/poisons.

III. Are all sicknesses caused by a virus? B. Malaria is a disease caused by parasitic protists called plasmodia. ○ 1. The symptoms of malaria include headache, shaking, chills, and fever. Some forms of malaria may lead to comas, convulsions, or even death. ○ 2. Malaria is transmitted by a mosquito. Any organism which transmits/carries a disease without being affected by the disease is called a vector.

III. Are all sicknesses caused by a virus? ○ 3. The life cycle of the plasmodia which cause malaria is complex. a. The infected mosquito bites a human. Plasmodia in the mosquito’s saliva enter the bloodstream. b. Plasmodia invade the liver and multiply. Then, plasmodia invade red blood cells and multiply. c. Red blood cells rupture, releasing plasmodia, which may then invade more red blood cells. d. Plasmodia develop into male and female forms that can infect mosquitos when they bite an infected human. e. Sexual reproduction in the mosquito’s intestine produce plasmodia which migrate to the salivary glands.

III. Are all sicknesses caused by a virus?  C. Candida is a yeast (fungus) that is one of the normal inhabitants of moist human epithelial tissue, such as the throat and vagina. Certain circumstances (such as change in pH or sudden decrease in helpful bacteria) can cause Candida to become pathogenic by growing too rapidly and releasing harmful substances. The condition caused by this growth is called candidiasis. Candidiasis leads to oral thrush, yeast infections, and/or kidney infections.

Review Questions  1. What bacterium causes more illness than any other bacterium?  Streptococcus  2. Name a disease caused by Streptococcus.  Strep Throat  3. What organism causes malaria?  Plasmodia  4. What is the vector of malaria?  Mosquito  5. What causes Candida to become pathogenic?  Change in ph or decrease of helpful bacteria

IV. How can I prevent these diseases, or get rid of them once I’m infected?  A. Your immune system allows your body to defend itself against most invaders. Your immune system includes lymph nodes which filter a fluid portion of your blood (called lymph) for invaders and special white blood cells which respond to any found invaders. ○ 1. An antigen is the term used to describe a foreign invader, such as a virus, bacteria, or pollen. ○ 2. Once the body detects the antigen, usually by trapping the antigen in a lymph node, special white blood cells called T-cells initiate the immune response by activating B-cells or destroying target cells on contact.

IV. How can I prevent these diseases, or get rid of them once I’m infected? ○ 3. B-cells perform two functions. a. Once a B-cell binds to the antigen (based on shape), the B-cell begins to produce antibodies. Antibodies are proteins that are specifically shaped to bind to the antigen and mark the antigen for destruction. b. The second type of B-cell is a memory B-cell. A memory B- cell will genetically “remember” the correct antibody. Then, if you are exposed to the same antigen, your body can more quickly respond.

IV. How can I prevent these diseases, or get rid of them once I’m infected? ○ 4. Active immunity develops when a person is exposed to microorganisms or foreign substances and the immune system responds. This happens in one of two ways: a. Antigens have entered the body before (either causing the disease or causing no symptoms). b. You receive a vaccine for the disease. Vaccines are weakened, dead, or fragments of microbes that are introduced to the body. By exposing the body to a weaker or similar version of the antigen, the body can produce antibodies and develop memory B-cells prior to an actual infection.

IV. How can I prevent these diseases, or get rid of them once I’m infected?  5. Passive immunity is acquired when antibodies are transferred from one person to another. This may happen from mother to child (across the placenta or through breast milk) or from a serum containing pre-formed antibodies (ex. antivenom).

IV. How can I prevent these diseases, or get rid of them once I’m infected? B. Medicines may be prescribed to help rid your body of the pathogen or to treat symptoms caused by the pathogen. ○ 1. Antibiotics destroy bacteria by creating holes in the bacteria cell wall or preventing protein synthesis within the bacteria cell (effectively shutting down the cell). ○ 2. Antiviral medicines interfere with the life cycle of the virus, stopping further damage. ○ 3. Anti-fungal medicines (such as Tinactin) destroy the fungal cells causing the diseases. ○ 4. Some medicines, such as pain-killers, treat only the symptoms of the disease.

IV. How can I prevent these diseases, or get rid of them once I’m infected?  C. The overall health of the host plays an important role in disease resistance, immune response, and the ability to treat diseases. One of the most important factors in maintaining optimal health is nutrition.  1. Nutrients provide essential chemicals for immune response and general health. For example, many vitamins are important co- enzymes. A balanced diet includes sources of the essential nutrients (such as proteins, carbohydrates, lipids, vitamins and minerals).  2. Poor nutrition leads to a weaker immune system. For example, a protein deficiency may mean the body cannot produce sufficient antibodies (which are proteins). Antibodies play a key role in defense against antigens. Malnutrition may lead to deficiency diseases, such as anemia (symptoms include fatigue) which is due to an iron deficiency.

Review Questions  1. What is an antigen?  A foreign invader to the body  2. What is an antibody?  Antibodies are proteins that are specifically shaped to bind to the antigen and mark the antigen for destruction.  3. What is the function of a T-cell? To activate B-Cells, or destroy target cells on contact  4. What is the function of the B-cell?  To produce antibodies  5. What is active immunity?  When a person is exposed to a foreign substance and the body responds  6. What is passive immunity?  When antibodies are passed from one person to another  7. What type of pathogen is killed by antibiotics?  Bacteria  8. What is one effect of poor nutrition?  Lead to a weaker immune system; Deficiency diseases