Bacteria characterized

  • Specific Bacterial Microorganisms Characteristics:

    • Bacillus subtilis:

    • Morphology: Bacilli (rods)

    • Cellular Arrangement: Chains

    • Gram Reaction: Gram-positive

    • Motility: Motile

    • Macroscopic Colony Color: Cream to brown

    • Micrococcus lutis:

    • Morphology: Cocci (spheres)

    • Cellular Arrangement: Tetrads

    • Gram Reaction: Gram-positive

    • Motility: Non-motile

    • Macroscopic Colony Color: Yellow

    • Escherichia coli (E. coli):

    • Morphology: Bacilli (rods)

    • Cellular Arrangement: Irregular

    • Gram Reaction: Gram-negative

    • Motility: Motile

    • Macroscopic Colony Color: Cream

    • Staphylococcus epidermis:

    • Morphology: Cocci

    • Cellular Arrangement: Staphylococci (clusters)

    • Gram Reaction: Gram-positive

    • Motility: Non-motile

    • Macroscopic Colony Color: Cream to white

    • Pseudomonas aeruginiso:

    • Morphology: Bacilli (rods)

    • Cellular Arrangement: Irregular

    • Gram Reaction: Gram-negative

    • Motility: Motile

    • Macroscopic Colony Color: Greenish-blue

    • Saradia macrosinens:

    • Morphology: Bacilli (rods)

    • Cellular Arrangement: Irregular

    • Gram Reaction: Gram-negative

    • Motility: Motile

    • Macroscopic Colony Color: Red (temperature-sensitive expression; produces red pigment at room temperature)

Exercise 7: Aseptic Transfer Techniques and Motility Testing

  • Key Vocabulary:

    • Pure Culture: A laboratory culture containing only a single isolated species or strain of microorganism.

    • Sterile Medium: A liquid or solid substance containing essential nutrients that is completely free of all living organisms.

    • Aseptic Technique: Specialized laboratory methods designed to prevent contamination by unwanted microbes and eliminate infection risks.

  • Aseptic Transfer Protocol:

    1. Flame-sterilize an inoculating loop by holding it in the inner blue cone (hottest part) of the Bunsen burner flame until glowing red.

    2. Allow the loop to cool completely in air without touching any surfaces.

    3. Flame the lip of the culture tube upon opening.

    4. Obtain a small sample of culture using the sterile loop.

    5. Inoculate the target sterile medium.

    6. Re-flame the lip of the target tube before capping.

    7. Re-sterilize the inoculating loop in the Bunsen burner flame, allow it to cool, and place it down.

  • Motility Testing Protocol:

    1. Sterilize a straight inoculating needle in the Bunsen burner flame and allow to cool.

    2. Pick up culture material on the tip of the needle.

    3. Insert the needle in a clean, straight stab line directly down into the motility agar medium (avoid any movement or zigzagging).

    4. Slowly withdraw the needle along the exact same path line.

    5. Sterilize the needle in the flame.

    6. Cap the test tube loosely to permit gas exchange.

    7. Interpretation of Motility:

    • Motile organisms grow outward away from the central stab line, clouding the medium.

    • Non-motile organisms display dense growth confined strictly along the initial stab line.

  • TSA Agar Slant Inoculation:

    1. Flame-sterilize inoculating loop and cool.

    2. Collect bacterial culture and flame test tube lip.

    3. Insert loop to the base of the agar slant, holding tube at an angle.

    4. Streak the surface from the bottom up in a continuous zigzag pattern.

    5. Flame tube lip, close cap loosely, and re-sterilize loop.

  • Four-Quadrant Isolation Streak Method:

    1. Purpose: To dilute bacterial population density sequentially across four quadrants, producing isolated individual cells that develop into pure single colonies.

    2. Sterilize loop, collect culture, and streak Quadrant 1.

    3. Flame loop to red-hot, allow to cool, rotate petri dish 90circ90^circ, pull twice from Quadrant 1 and streak Quadrant 2.

    4. Flame loop, cool, rotate dish 90circ90^circ, pull twice from Quadrant 2 and streak Quadrant 3.

    5. Flame loop, cool, rotate dish 90circ90^circ, pull twice from Quadrant 3 and streak Quadrant 4.

    6. Note: Do not re-dip into original stock culture between quadrants; flame loop every time to achieve serial dilution.

Exercise 10: Parasitology and Parasitic Life Cycles

  • General Definition:

    • Parasite: An organism that lives on or inside another host organism, deriving nutrients at the host's expense.

  • Plasmodium vivax and Plasmodium Life Cycle Stages:

    1. Sporozoites: Infectious stage injected into human bloodstream during a bite by an infected female mosquito; travel directly to the liver to invade hepatocytes.

    2. Merozoites: Released from ruptured liver cells to invade human red blood cells (RBCs), initiating the symptomatic blood-stage infection.

    3. Trophozoites: Active feeding and growing stage inside infected RBCs; develop into schizonts which trigger classic symptoms of malaria.

    4. Gametocytes: Sexual precursor stage produced in red blood cells; ingested by a female mosquito during a blood meal to complete and restart the developmental cycle.

    • Special Characteristic of Plasmodium vivax: Certain sporozoites differentiate in liver cells into dormant forms termed hypnozoites. These hypnozoites remain dormant for weeks or months, reactivating later to cause disease relapses without requiring a new mosquito bite.

  • Diagnostic Characteristics of Specific Parasites:

    • Trypanosoma cruzi:

    • Microscopic Appearance: Thin, C-shaped or S-shaped flagellated organism observed in blood smears, featuring a distinctive large kinetoplast.

    • Borrelia burgdorferi:

    • Microscopic Appearance: Spirochete; thin, flexible, wavy, corkscrew-shaped spiral bacterium.

    • Schistoma mansoni:

    • Egg Stage: Oval-shaped egg displaying a prominent, large lateral spine projecting from the shell.

    • Adult Stage: Trematode (fluke) morphology.

    • Fasciola heptica:

    • Adult Stage: Flat, leaf-shaped fluke body structure.

    • Egg Stage: Large, broad oval egg, characteristic yellow to brown color.

    • Enterobius vermiculares (Pinworm):

    • Adult Stage: Small, white, thread-like nematode worm featuring a sharply pointed tail end.

    • Egg Stage: Elongated, asymmetrical, D-shaped egg (flattened on one side and convex on the other).

    • Nector americanus (Hookworm):

    • Life Cycle: Adult worms inhabit human small intestine →\rightarrow eggs passed out in host feces $ ightarrow$ eggs hatch in warm, moist soil $ ightarrow$ develop into infectious L3 filiform larvae $ ightarrow$ filiform larvae penetrate bare human skin $ ightarrow$ enter venous circulation to heart $ ightarrow$ migrate into lungs $ ightarrow$ ascend pharynx and are swallowed $ ightarrow$ pass back into small intestine to reach adulthood.

    • Egg Stage: Colorless, thin-shelled egg containing a distinct clear internal cleavage space.

    • Trinella spiralis:

    • Life Cycle: Ingestion of raw or undercooked meat containing encysted larvae $ ightarrow$ stomach acids digest cyst capsule releasing larvae $ ightarrow$ larvae mature into adult worms in small intestine $ ightarrow$ adult females produce live larvae $ ightarrow$ larvae enter lymphatic and blood circulation $ ightarrow$ migrate into host skeletal muscle tissue.

    • Microscopic Appearance: Coiled C-shaped encysted larvae embedded inside skeletal muscle fibers.

    • A cholestoma caninum (Dog Hookworm):

    • Primary Host: Canines (dogs).

    • Microscopic Appearance: Eggs resemble Nector americanus; adult worm possesses a large buccal capsule (mouth) containing three distinct pairs of teeth.

    • Dipylidium caninum (Tapeworm):

    • Transmission and Host: Transmitted via ingestion of infected fleas; common in dogs and cats.

    • Adult Stage: Long, flat, segmented tapeworm; individual proglottid segments resemble cucumber seeds or rice grains.

    • Egg Stage: Diagnostic egg packets containing multiple eggs grouped together inside protective membranes.