Bacterial cell morphology and structure

Question 1

How big are bacteria?

Answer 1

1-10 micrometers

Question 2

What are the shapes of the bacteria: cocci, bacilli, spirilla and spirochetes, coccobacillus

Answer 2

-cocci = spherical or oval
-bacilli = rod
-spirilla and spirochetes = spiral
-coccobacillus = short rods

Question 3

Arrangements of bacterial cells: Staphylococci, diplococci, streptococci, tetrad, sarcina

Answer 3

-Staphylo = clusters (grape like bundles)
-Diplococci = two cells
- strepto = chain-like
-tetrad = squares
-sarcina = circles

Question 4

How do we observe bacteria?

Answer 4

-light microscopy
-in brightfield microscopy light is transmitting through the bacteria and in dark field microscopy light is reflected differently

-Fluorescence microscopy: UV stimulation, release of light at longer wavelengths
-Natural fluorescence or labeled “tag”

Electron microscopy: Transmission EM is very high resolution of internal structures. Scanning EM is high resolution at the surface.

Question 5

Gram staining of bacteria

Answer 5

Multi-step process

1) Primary stain: -Crystal violet
2) Mordant (fixes the dye): -iodine
3) Decolorizing agent: Alcohol/ acetone.( thick peptidoglycan of gram + organisms retain this purple dye)
4) Counter stain: -Safranin (gram + remains purple, gram - becomes pink)

-Gram positive bacteria have a uniformly dense cell wall consisting primarily of peptidoglycan.
-Gram negative bacteria have a very thin peptidoglycan layer and an outer membrane. Therefore they do not have enough peptidoglycan to absorb the purple)

Question 6

Non-Gram Staining Bacteria

Answer 6

-Mycoplasma: lacks cell wall. Do not have a cell wall and therefore cannot be gram-stained.
-Mycobacterium tuberculosis (use Acid-fast stain): Have thick, waxy, lipid rich cell wall thats resistant to gram staining)

Question 7

Acid-fast stain

Answer 7

-specific stain for mycobacterium
-also a multi-step process
1) Apply carbolfuchsin (primary stain)
2) Apply heat (mordant)
3) Apply acid alcohol (decolorizer)
4) Apply methylene blue (counter stain). Acid fast bacteria appear pink

Question 8

General bacterial cell structure and function: Cell wall, Membrane, Ribosomes, Nucleoid, storage granules, pili/ fimbriae, flagella, capsule

Answer 8

Cell wall: functions in rigidity and prevents osmotic lysis. Necessary for cell life.

Membrane: functions in osmotic barrier, transport, and energy. Needed for cell life.

Ribosomes: Functions in protein synthesis. Needed for cell life.

Nucleoid: Functions in genetic material. Needed for cell life.

Storage granules: Functions in energy storage. Not needed for cell life.

Pili, fimbriae: Functions in adherence, mate and secretion. Not needed for cell life

Flagella: Functions in motility and chemotaxis. Not needed for cell life.

Capsule: Functions in anti-phagocytosis and adherence. Not needed for cell life.

Question 9

Cell membrane/ Plasma membrane

Answer 9

-Chemical components: Phospholipids, proteins (70%) and no cholesterol

-Functions: Osmotic barrier, transporters, and energy production

Question 10

Cell wall

Answer 10

-Peptidoglycan unique component to bacteria – target for penicillins (makes it a good therapeutic target).
-rigid matrix consisting polymer of muramic acids, NAG and NAM, cross-linked by tetrapeptide cross-linkages.
-rigidity and shape
-prevent osmotic lysis
-essential for survival

Question 11

Peptide chemical structure

Answer 11

Gram negative bacteria: have thin peptidoglycan layer with a small linkage between peptides

Gram positive bacteria: thick peptidoglycan layer with a peptide interbridge

Question 12

Structural differences between Gram + and Gram -

Answer 12

Gram + : thick cell wall Gram - : thin cell wall
teichoic acid no teichoic acid
one cell membrane two cell membranes
no periplasmic space periplasmic space
no lipopolysacharides Lipopolysacharides

Question 13

Lipopolysaccharide - LPS

Answer 13

-Most abundant cell envelope component in Gram neg bacteria
-Extremely toxic endotoxin and cause fever and shock
-lipid A is the toxic moiety of LPS (immuno-active portion)
-O-antigen is the part that extends out of the surface of the bacteria. Varies between species, and even strains. Antigenic determinants.

Question 14

Capsule

Answer 14

-A layer of polysaccharide or polypeptide attached to cell wall. (external to the wall)
-Thick-capsule: thin-slime layer, hydrophilic, transparent, not readily stained.
-Functions: resist phagocytic engulfment from WBC, Antigenic, Protect bacteria from dehydration and adhere to surfaces to form colonies
-capsules are sticky and can help form biofilm/ plaque in the oral cavity

Question 15

Pili (fimbriae)

Answer 15

-hollow, hair-like structures on the cell surface
-2 types: Common/ attachment pili and sex pili
-common pili are often adhesins essential for colonization.
-Sex pili: exchange of genetic materials between gram- bacteria

Question 16

Flagella

Answer 16

-organelles of motility (The way bacteria can move around)
-find favorable environments
-reside on the cell surface of some bacteria
-can be external or internal
- Complex structures
-Some organisms have different amounts and different placements of flagella.
-spirochetes have their flagella on the inside which is why they are spiral in shape because the flagella are very wound
-Gram negative bacterium have more components due to the complexity of the cell membrane layers