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micro_db2 > Bacterial Morphology & Physiology > Flashcards

Bacterial Morphology & Physiology Flashcards

1
Q

What is bacterial morphology?

A

Bacterial morphology is the study of bacterial cell shape and structure

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2
Q

Why is bacterial morphology relevant to medicine?

A

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

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3
Q

What are the characters of prokaryotes?

A
  • No nucleus
  • Cell wall
  • No cell organelles
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4
Q

What are the characters of eukaryotes?

A
  • Nucleus
  • No Cell wall
  • cell organelles e.g. Mitochondria, chloroplasts, endoplasmic reticulum.
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5
Q

What is Gram stain?

A

Gram stain is most important differential staining method in microbiology

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6
Q

What are steps of Gram stain?

A

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.

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7
Q

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

A

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

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8
Q

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

A

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

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9
Q

Do all bacteria can be stained with Gram stain?

A
  • 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
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10
Q

What are the bacterial cell shapes?

A
  • Cocci (spherical)
  • Bacilli (rod shaped)
  • Curved or spiral shaped
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11
Q

What is bacterial cell structure?

A
  • 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
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12
Q

What are the components of cytoplasmic membrane?

A

Composed primarily of lipids and phospholipids

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13
Q

What is the function of cytoplasmic membrane?

A
  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
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14
Q

What are the components of bacterial cell wall?

A

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.

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15
Q

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

A
  • Gram Positive: Many layers of Peptidoglycan ( 90% of cell envelope)
  • Gram Negative: One Peptidoglycan layer( 2-20% of cell envelope)
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16
Q

What is Gram-positive cell envelope?

A
  • 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
17
Q

What is Gram-negative cell envelope outer membrane ?

A

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

18
Q

What is the Gram negative sepsis?

A
  • 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.
19
Q

What are cell Appendages and other cell structures?

A

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

20
Q

What is flagellar movement?

A
  • Bacteria use flagella to swim

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

21
Q

What are types of pili?

A
  • Common pili (adherence)

* Conjugative Pili (plasmid transfer)

22
Q

What are bacterial spores?

A
  • 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
23
Q

What is the function of bacterial spores?

A

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

24
Q

What are capsules and slime?

A

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

25
Q

What are bacterial biofilms?

A
  • 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
26
Q

How can bacteria divide?

A

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
27
Q

How does bacterial growth proceed?

A

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.

28
Q

What are the bacterial culture growth phases?

A 
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
29
Q

What are the requirements for bacterial cells to grow?

A

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

30
Q

What are the nutrient requirements for bacterial cells?

A

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)

31
Q

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

A
  • 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).
32
Q

How can energy be provided for bacterial growth?

A
  • 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
33
Q

What is metabolism?

A

Catabolism + Anabolism = Metabolism

34
Q

Why bacteria need energy?

A 
Bacterial Energy Production
ATP synthesis required for:
•	  Metabolic Processes
•	  Flagellum Movement
•	  Nutrient Transport
35
Q

What are principals of ATP synthesis during oxidative phosphorylation?

A
  • 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
36
Q

What is anaerobic respiration?

A

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

37
Q

What is fermentation?

A
  • Cytochrome electron transfer pathways not involved
  • Organic acids used as terminal electron acceptors
  • Products include ethanol, acetic acid and butyric acid
38
Q

What is the summary of bacterial morphology & physiology?

A
  • 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

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