2. Bacterial Anatomy Flashcards
What are the three basic shapes of bacteria?
Cocci (round), rods (long), and spirilla (spiral)
What are the characteristic arrangements of cocci?
Chains Clusters Pairs (diplococci) Tetrads - groups of 4 Sarcinae - cubes of eight
What are the characteristic arrangements of rods?
Can have round ends, square ends, pointed ends.
Palisades - lie in sheets on top of each other
Acute angles - snap at point of division
Chaining
What are the characteristic shapes of spirilla?
Can vary from a slightly curved rod to a tight corkscrew.
What are involution forms?
Dead, degenerating, or dying bacteria.
Have weird bizarre forms.
Result of poor growth conditions, lack of nutrients, or antibiotic treatment.
Define cellular morphology. How are bacteria measured?
The size, shape, and arrangement.
Measured in micrometers.
What is a bacterial colony?
Group of bacteria that divide and grow together to form a visible round entity.
What is cellular morphology?
Microscopic appearance of bacteria on gram stained slides.
What is colonial morphology?
Macroscopic appearance of bacterial colonies after incubation.
Includes colour, consistency, hemolysis, size, edge appearance, etc.
What are flagella?
Long, thin, filamentous appendages that enable bacteria to move.
Is anchored to the call wall and cytoplasmic membrane.
What are the different arrangements of flagella on a bacterial cell?
Atrichous - none
Monotrichous - one, rapid darting directional movement
Lophotrichous - up to 6 on one end, rapid and more directional movement
Amphitrichous - both ends
Peritrichous - around, tumbling motion
Where are flagella found?
Some rods and spirals
Not cocci
What is motility?
The ability to move spontaneously and actively while consuming energy in the process.
Bacteria often rest between periods of motility.
Name and describe the two methods of determining motility.
Slide motility - look at a liquid culture microscopically
Motility media - inoculate a soft medium and observe for growth spreading in the medium
When is the best time to observe bacteria using slide motility?
During the log phase at room temperature.
Use 40x magnification
What are the tree types of movement that can be seen in a slide motility preparation?
Brownian movement - bacteria appear to vibrate or jiggle
Drifting or streaming - moves in flow with the liquid
Stages of slide motility - not all bacteria will be moving at the same time, reset period may occur, bacteria move against currents
What are some advantages and disadvantages of slide motility?
Advantages - rapid results, can tell the flagellar arrangements
Disadvantages - tedious and slow, may not show motility if bacteria have passed the log phase
What is motility media?
A semi solid nutrient medium that is clear enough to see the growth of bacteria
What are two methods of descending motility medium?
Plate method - single plate of medium used, incubated for 1-2 days
Tube method* - medium is inoculated with a straight wire about half way down a tube, incubated for 1-2 days, TTC may be added to give a red colour to better detect where growth has spread
What are the advantages and disadvantages of using the media method?
Advantages - fast and easy, tube can give optimum conditions for motility
Disadvantages - some bacteria do not grow well below the surface of the medium
What are bacterial capsules?
A viscous layer surrounding bacteria excreted from the cell (called glycocalyx). Must be organized and firmly attached to the cell wall to be called a capsule.
What is the function(s) of bacterial capsules?
Interfere with phagocytosis
Increases virulence
May provide a protective layer
What do colonies of capsulated bacteria look like in the lab?
Mucoid and slimy
Wet glistening appearance
What are two problems that can occur in the lab when trying to detect capsules?
Shrinkage - caused by heat, drying and fixing to a slide. Can be prevented by using a wet preparation.
Development - most often present on the initial culture medium but may lack in subsequent cultures, good carbon and energy sources are needed, sucrose added to promote production
What is negative staining?
The part of the cell you want to demonstrate remains unstained while all other material is stained.
What substance is used in negative staining to view capsules?
India Ink (Negrosin)
Capsules appear as clear halos
What is the composition of a bacterial cell?
Have a rigid layer outside the plasma membrane called the cell wall
The cell wall has a strengthening substance called Peptidoglycan
NAG and NAM are two sugars that make up the carbohydrate backbone
What two groups are bacteria divided into when Gram staining?
Gram positive
Gram negative
This is based on their colour after Gram staining in the lab
How can bacterial cell walls be damaged?
Antibiotics - able to break the Peptidoglycan of the cell wall
Enzymes - lysozyme can break bonds between sugars and Peptidoglycan
A Gram + cell wall is more susceptible than a Gram - cell wall as the Peptidoglycan is exposed on a Gram positive cell
What is a Gram positive cell that has lost the cell wall called?
A protoplast
What is it called when gram negative cell has its membrane broken down but some the outer layer remains attached?
A spheroplast
What is a hypotonic solution vs. a hypertonic solution?
Hypotonic - water moves into the cell due to a lower concentration of water in the cell, causing rupture
Hypertonic - water leaves the cell due to a higher concentration of water within the cell, causes shrinkage and collapse
Both are lethal to bacterial cells
What is an isotonic solution?
Has the same concentration of salt as inside the cell, no water moves in or out
Describe step 1 of the Gram staining procedure.
- Fix slide with crystal violet (C)
- stain left on for 1 minute then washed with water
- all cells are now stained deep purple
Describe step 2 of the Gram staining procedure.
2.
- flood the slide with Gram’s or Lugol’s Iodine solution for 1 minute and wash off with water
- mordant: a substance that fixes dye to a cell
- cells at this stage are stained purple to bluish-black
Describe step 3 of Gram staining.
- Is the most important step
- decolourize with acetone-alcohol (A) until no more blue colour can be seen coming off the slide
- this is when differentiation takes place
- Gram positive remain purple-blue
- Gram negative decolourize and become colourless
Describe step 4 of the Gram staining process.
- counter stain with safranin (red) (S) for 1 minute
- Gram positive cells appear purple to bluish-black
- Gram negative cells appear pink to red
- first examined under a microscope at 10x
- once suitable areas are found, examine with oil immersion (100x)
What is the KOH (potassium hydroxide) test?
A drop of KOH is placed on a slide and stirred with a straight wire. Gram negative organisms form a thread when the wire is pulled away because there is more lipid on the Gram neg cell wall.
Explain the theory of the Gram stain reaction.
An intact cell wall is necessary to differentiate Gram positive and Gram negative bacteria.
What are the differences between Gram negative bacteria and Gram positive bacteria?
Thickness of cell wall - Gram + thick, Gram - thin
Amount of Peptidoglycan - Gram + thick layer, Gram - thin layer
Amount of lipid - Gram + little, Gram - lots
What nuclear material is included in a bacterial cell?
Chromosome - genetic material
Plasmids - aid in the survival of the cell, resistance to antibiotics, mate and exchange genetic info, produce toxins harmful to host cells
What are Fimbriae and Pilli?
Fimbriae - non-flagellar hair-like structures usually found uniformly over the entire cell surface
Pili - longer structures than Fimbriae and only one or two per cell, often called sex pili as they form the connection between two cells when DNA is being exchanged
What are the 4 processed used in bacterial cells to move materials a cross the cytoplasmic membrane?
Diffusion - passive movement from high to low concentration
Osmosis - passive movement of water
Facilitated Diffusion - passive movement from area of high to low concentration using carrier enzymes
Active Transport - requires energy, transport material from areas of low to high concentration
What are bacterial spores?
One copy of the chromosome and a small amount of cytoplasm are isolated and when germination occurs the spore separates and becomes a cell
Gram positive rods are the only bacteria capable of producing spores (endospore)
Best time to see spores are during the death phase and are resistant to staining
What are the functions of spores?
Enable bacteria to resist adverse conditions.
Heat, disinfectants, lack of nutrients, drying
Do bacteria have ribosomes?
Yes!
