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Micromorphology

Before you play an 18-hole game of golf you need to learn how to swing. This lab is intended to increase your microscopy skills. Many of the bacteria you will be looking at are taken from clinical samples. Their morphology is often the first step in their diagnostic identification. The prepared slides you are viewing have all been stained. You will be doing several of these same stains in lab in the next few weeks. Look (and record) how the cells are distributed on the slide, at the intensity of the stains, at the size and shape of the cells, for special features and how the cells are arranged together.

Please remember that bacteria rarely exist by themselves as you see them on these slides. They live in consortiums with other species of bacteria and can form complex structural communities.

You have 12 slides to view in this exercise. You can choose to individually focus all 12 slides or each of you can focus three slides and observe one another’s specimens. Teamwork - divide and conquer. You can access images from the slides we have here in the lab on the website, pictures may also be available in lab.

  1. Bacteria, yeast, and blood: This mixed smear shows typical bacilli, yeast, and human blood cells. Pay particular attention to their respective sizes. Even the biggest bacteria are smaller than yeast, which are still smaller than a typical human red blood cell.
  2. Staphylococcus aureus: This smear shows typical Gram positive cocci. Staph aureus is frequently found in the human respiratory tract and on the skin.
  3. Micrococcus luteus: These Gram positive cocci, typically arranged in tetrads, are normal flora of mammalian skin.
  4. Streptococcus faecalis: Shows typical chains of cocci.
  5. Mycobacterium tuberculosis: These Gram-resistant, slightly curved bacilli are the causative agents of tuberculosis. Due to a special wax in their cell membrane, these organisms do not readily take up dye from a typical gram stain. Instead, an acid-fast stain using either heat or detergent is performed in order to break through this protective waxy layer.
  6. Pseudomonas aeruginosa: These Gram negative, slightly curved bacilli cause infections in wounds, burns, and urinary tracts.
  7. Clostridium tetani: observe the characteristic drumstick shape of these cells. The endospores are round and terminal. These anaerobes are the causative agent of tetanus.
  8. Bacillus anthracis: These long chains of rod-shaped cells have centrally located endospores. Endospores are a resting structure formed inside the cell that allows the bacteria to survive harsh conditions for extended periods. Look for red spores inside blue rods.
  9. Treponema pallidum: is the causative of syphilis. It is a spirochete that is best viewed live with dark-field microscopy.
  10. Bacterial Capsules: notice the background of the slide is colored so that you can see the protective slime coating secreted by many bacteria.
  11. Bacterial flagella (peritrichous): many bacteria are motile because they possess whip like flagella. They may be distributed all over the cell, peritrichous, or just tufts of flagella at both ends, amphitrichous. This is a very difficult and time-consuming stain because the flagella are very thin and fragile.
  12. Bacterial flagella (amphitrichous): many bacteria are motile because they possess whip like flagella. They may be distributed all over the cell, peritrichous, or just tufts of flagella at both ends, amphitrichous. This is a very difficult and time-consuming stain because the flagella are very thin and fragile.