Biol 251 - Microbiology Lab

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Micro-Morphology

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 20 slides to view in this exercise. You can choose to individually focus all 20 slides or each group of 4 can focus 5 slides each and observe one anotherís specimens. Teamwork - divide and conquer! You can click on most of the names and get an image from the slides we have here in the lab. Hit the back button on the menu bar to return to this page.

General Structure

  • 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.
  • Bacterial Types - This smear is a mix of typical bacilli, cocci, and spirillium.

Cocci

  • Staphylococcus aureus - This smear shows typical gram positive cocci. Staph. aureus is frequently found in the human respiratory tract and on the skin.
  • Micrococcus luteus - These gram positive cocci, typically arranged in tetrads, are normal flora of mammalian skin.
  • Neisseria gonorrhoeae - These gram negative diplococci are the causative agent of gonorrhea. This is a smear of pus from a lesion. Look for kidney shaped pairs of cocci. The cells are flattened where they are adjacent.
  • Streptococcus faecalis - Shows typical chains of cocci.

Bacilli

  • Bacillus - This mixed smear shows typical gram positive and gram negative bacilli.
  • 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. These spore-forming streptobacilli are the causative agent of anthrax.
  • Clostridium tetani - Observe the characteristic drumstick shape of these cells. The endospores are round and terminal. These anaerobes are the causative agent of tetanus.
  • Mixed Coliforms - Mixed smear showing various species of bacteria found in the human intestine; indicates fecal contamination in water supplies.
  • 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 detergant is performed in order to break through this protective waxy layer.
  • Pseudomonas aeruginosa - These gram negative, slightly curved bacilli cause infections in wounds, burns, and urinary tracts.

Spirochetes, Helicals, Spirillium, Vibrio

  • Borrelia burgdorferi - The causative agent of Lymeís disease. It is about 0.3 micrometers in diameter and 15 micrometers in length. Its helical structure stands out against the RBCís.
  • Treponema pallidum - The causative of syphilis. It is a spirochete that is best viewed live with dark-field microscopy.
  • Typical Spirillium - Smear showing typical spirillium bacteria.
  • Vibrio cholerae - These comma-shaped gram negative rods are the causative agent of Cholera.

Flagella, Capsules, Archae

  • Bacterial Capsules - Notice the background of the slide is colored so that you can see the protective slime coating secreted by many bacteria.
  • Bacterial Flagella (Peritrichous) - Many bacteria are motile because they possess whip-like flagella. Peritrichous flagella are distributed all over the cell; monotrichous flagella indicate just one; tufts of flagella at both ends of the cell are amphitrichous; and tufts of flagella at one end of the cell are lophotrichous. This is a very difficult and time-consuming stain because the flagella are very thin and fragile.
  • Bacterial Flagella (Polar Amphitrichous) - Many bacteria are motile because they possess whip-like flagella. Peritrichous flagella are distributed all over the cell; monotrichous flagella indicate just one; tufts of flagella at both ends of the cell are amphitrichous; and tufts of flagella at one end of the cell are lophotrichous. This is a very difficult and time-consuming stain because the flagella are very thin and fragile.
  • Archaebacteria - This is a collection of ancient bacteria. Look for rods, cocci and involuted, often square shaped cells. The species represented here are extreme halophiles (salt-lovers) and methangens (able to live off of methane).
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