Bacterial Morphology & Physiology

Question 1

What is bacterial morphology?

Answer 1

Bacterial morphology is the study of bacterial cell shape and structure

Question 2

Why is bacterial morphology relevant to medicine?

Answer 2

We need to understand bacterial cell structure as part of our understanding of how bacteria cause disease and how we can eradicate bacteria using antibiotics

Question 3

What are the characters of prokaryotes?

Answer 3

• No nucleus
• Cell wall
• No cell organelles

Question 4

What are the characters of eukaryotes?

Answer 4

• Nucleus
• No Cell wall
• cell organelles e.g. Mitochondria, chloroplasts, endoplasmic reticulum.

Question 5

What is Gram stain?

Answer 5

Gram stain is most important differential staining method in microbiology

Question 6

What are steps of Gram stain?

Answer 6

1: Begin with heat fixed cells.
2: Flood slide with crystal violet dye for 1 min.
3: Add iodine solution for 1 min.
4: Wash slide with alcohol for 20 sec.
5: Counter stain with safranin.

Question 7

What is the end result of gram stain on Gram positive bacteria?

Answer 7

Violet color (crystal violet iodine complex forms within the cells due to high peptidoglycan content and low lipid content)

Question 8

What is the end result of gram stain on Gram negative bacteria?

Answer 8

Red color (red safranin color due to washing out of alcohol of crystal violet, low peptidoglycan content and high lipid content)

Question 9

Do all bacteria can be stained with Gram stain?

Answer 9

• Some bacteria don’t stain using the Gram method
• Mycobacteria have a high wax content in their cell envelope and suspected mycobacteria are stained using the Ziehl-Neelsen stain
• Mycoplasmas, the smallest known bacteria, have no cell wall to stain

Question 10

What are the bacterial cell shapes?

Answer 10

• Cocci (spherical)
• Bacilli (rod shaped)
• Curved or spiral shaped

Question 11

What is bacterial cell structure?

Answer 11

• Genome
  The bacterial genome or chromosome contains the bacterial genetic information Plasmids may also be present:
• Cytoplasmic Membrane
  The cytoplasmic membrane surrounds the cytoplasm
• Cell Wall
  Rigid layer surrounding the cytoplasmic membrane
• Outer Membrane of Gram-negative bacteria
  Covers the cell wall and acts as a molecular sieve

Question 12

What are the components of cytoplasmic membrane?

Answer 12

Composed primarily of lipids and phospholipids

Question 13

What is the function of cytoplasmic membrane?

Answer 13

1. Osmotic barrier
   
   • Only molecules smaller than glycerol diffuse into the cytoplasm
2. Site of energy production (oxidative phosphorylation)
3. Transport of important molecules via PERMEASES
   
   • Facilitated diffusion (passive) and Active transport
4. Synthesis of new cell wall
5. Anchor the chromosome

Question 14

What are the components of bacterial cell wall?

Answer 14

Peptidoglycan is the principal component of bacterial cell wall. It is a unique polysaccharide which gives the cells its characteristic shape and prevents osmotic lysis.

Question 15

Do Gram positive and Gram negative bacteria have the same percent of Peptidoglycan?

Answer 15

• Gram Positive: Many layers of Peptidoglycan ( 90% of cell envelope)
• Gram Negative: One Peptidoglycan layer( 2-20% of cell envelope)

Question 16

What is Gram-positive cell envelope?

Answer 16

• Multiple layers of peptidoglycan
• Teichoic acids and Lipoteichoic acids  Extend into the environment around the cell
• Adherence
• Antigenic determinants
• Gram-positive sepsis - cell wall fragments containing teichoic acids can elicit an inflammatory response similar to LPS sepsis

Question 17

What is Gram-negative cell envelope outer membrane ?

Answer 17

Phospholipid-Lipopolysaccharide (LPS) bilayer (extra lipid layer - mechanism of the Gram stain)
• Bacterial cell adhesion
• Resistance to phagocytosis
• Molecular sieve - access of some molecules to cell wall and cytoplasmic membrane

Question 18

What is the Gram negative sepsis?

Answer 18

• Caused by LPS or endotoxin
• Binds to LPS binding protein on monocyte and macrophage cell surface.
• Immune cell activation and production of inflammatory mediators
• Systemic toxic effects such as fever, hypotension, and rapid death.

Question 19

What are cell Appendages and other cell structures?

Answer 19

Flagella and Pili extend from the cell surface
• Flagellae rotate and are required for motility (chemotaxis)
Bacteria swim towards chemo-attractants and away from chemorepellents

Question 20

What is flagellar movement?

Answer 20

• Bacteria use flagella to swim

* Changing the direction of flagellar rotation can cause the cell to tumble and change direction.

Question 21

What are types of pili?

Answer 21

• Common pili (adherence)

* Conjugative Pili (plasmid transfer)

Question 22

What are bacterial spores?

Answer 22

• Some Gram-positive bacteria can form Spores which provide protection from adverse conditions
• Spores introduced into a wound site can germinate and cause infection
• Gram-negative bacteria cannot form spores

Question 23

What is the function of bacterial spores?

Answer 23

Although harmless themselves until they germinate, they are involved in the transmission of some diseases to humans including:
• Anthrax: caused by Bacillus anthracis
• Tetanus: caused by Clostridium tetani
• Botulism: caused by Clostridium botulinum
• Gas gangrene: caused by Clostridium perfringens

Question 24

What are capsules and slime?

Answer 24

Capsules (tightly associated) and Slime (loosely associated) are polysaccharide or protein layers surrounding many bacterial cells
• Provide protection from phagocytosis and antibiotics
• Play a role in bacterial adherence

Question 25

What are bacterial biofilms?

Answer 25

* The formation of a slime layer is indicative of biofilm formation * The majority of bacterial infections treated by clinicians involve biofilms * Pseudomonas aeruginosa infections in cystic fibrosis patients * Staphylococcus epidermidis catheter related infections

Question 26

How can bacteria divide?

Answer 26

Bacteria divide by Binary Fission - Binary Fission - Chromosome divides to produce two identical copies - These copies segregate to opposite ends of the cell - Cell wall is laid down the middle of the cell to ultimately produce two new cells which are identical

Question 27

How does bacterial growth proceed?

Answer 27

Bacterial growth proceeds exponentially • Generation times can be as fast as 20 minutes • Contributes to the remarkable adaptability of bacteria Growth in a hostile environment can create a selective pressure for mutant cells which can persist. One mutant cell which can survive will rapidly grow and take over.

Question 28

What are the bacterial culture growth phases?

Answer 28

``` 1. Lag Phase • Adaptation 2. Logarithmic Phase • Cells multiply at the maximum rate 3. Stationary Phase • Lack of nutrients and buildup of toxic metabolic intermediates means multiplication is balanced by cell death 4. Phase of decline ```

Question 29

What are the requirements for bacterial cells to grow?

Answer 29

For Bacterial Cells to Grow they require: 1. energy 2. the building blocks required for the construction of cellular machinery and 3. appropriate environmental conditions

Question 30

What are the nutrient requirements for bacterial cells?

Answer 30

Nutrient Requirements • Water • Carbon (carbohydrate) • Nitrogen (protein) • Inorganic salts • Iron –sequestered by siderophores (= Siderophores are small, high-affinity iron-chelating compounds secreted by microorganisms such as bacteria and fungi and serving to transport iron across cell membranes) • Oxidation of organic compounds (carbohydrates, lipids, proteins)

Question 31

What is the impact of nutritional requirements on the growth of bacteria?

Answer 31

* The ability of individual bacterial species to produce their own cellular components will dictate its nutritional requirements * E.g. some species can synthesis all essential amino acids whereas others need amino acids to be added to their growth media (auxotrophs).

Question 32

How can energy be provided for bacterial growth?

Answer 32

* Derived from the enzymatic breakdown of organic substrates (carbohydrates, lipids or proteins) in a process called Catabolism * Energy generated from catabolism is used to synthesise cellular constituents in a process called anabolism

Question 33

What is metabolism?

Answer 33

Catabolism + Anabolism = Metabolism

Question 34

Why bacteria need energy?

Answer 34

``` Bacterial Energy Production ATP synthesis required for: • Metabolic Processes • Flagellum Movement • Nutrient Transport ```

Question 35

What are principals of ATP synthesis during oxidative phosphorylation?

Answer 35

* Electrons passing through ETC’s provides energy to move protons outside the cytoplasmic membrane * Creates proton gradient * Protons return to cytoplasm through special proton channels to balance the gradient generating energy for ATP synthesis

Question 36

What is anaerobic respiration?

Answer 36

Obligate anaerobes are sensitive to superoxide radicals -lack Superoxide dismutase (important antioxidant defence against oxidative stress in the body) • Alternative electron acceptors are used instead of oxygen (eg NO2) • Different cytochrome electron transport chains are employed

Question 37

What is fermentation?

Answer 37

* Cytochrome electron transfer pathways not involved * Organic acids used as terminal electron acceptors * Products include ethanol, acetic acid and butyric acid

Question 38

What is the summary of bacterial morphology & physiology?

Answer 38

* Different genera of bacteria can be differentiated from one another on the basis of their cell shape, how they are arranged when viewed by microscopy and Gram stain result * Gram-positive and Gram-negative bacteria differ from another in the structure of their cell envelope (cell envelope = cytoplasmic membrane, cell wall (thicker in Gram-positives) and outer membrane (only in Gram-negatives) * Bacteria can possess pilli to aid in attachment, flagellae for movement, some can produce spores for survival and most can produce a biofilm. All important factors in pathogenesis of infection and for treatment * Bacterial cells can multiply rapidly, utilise different nutrients and pathways for energy (ATP) production and some can vary their oxygen requirements during respiration