03 Bacteria structure

Question 1

Peptidoglycan *

Answer 1

Peptidoglycan *

• Only in bacterial cell wall
• Gives rigidity, shape
• Helps resist low osmotic pressure *
• Target for cell-wall synthesis inhibiting antimicrobials *
  
  • Penicillins
  • Cephalosporins
  • Vancomycin
  • These inhibit transpeptidase enzyme that cross-links the peptide chains
• Target of lysozyme
  
  • Human tears, mucous, saliva
  • Cleaves peptidoglycan

Question 2

Bacterial Cell components

Answer 2

Bacterial Cell components

• Capsule
  
  • structure:
    
    • slim layer
    • glycocalyx
  • Composition
    
    • Polysaccharide*

(important exception – anthrax capsule = glutamic acid)

* function
    * Prevents phagocytosis \* (until bacterium is opsonized)
    * immunogenic\* ( ability of a particular substance, such as an antigen or epitope, to provoke an immune response)​​​

• Cell wall
  
  • 1) Peptidoglycan*
    
    • Thick in Gram positives
    • Thin in gram negatives
• composition
  
  • Repeating units of NAG+NAM with peptide chains that are cross-linked
• function
  
  • Rigidity
  • shape
  • protects against osmotic pressure
• 2) Teichoic acids (Only gram positives)
  
  • function:
    
    • Immunogenic
    • Induces TNF-α, IL-1
• 3) Outter membrain (only in gram negative)
  
  • ​composition
• Lipopolysaccharide (LPS)- Lipid A - toxic moiety*
• “O” antigen (somatic)
  
  • Polysaccaride
• Outer memb. proteins
• Porins ​

function

• Hydrophobic barrier

- LPS = ENDOTOXIN* (lipid A has the toxic effect)

• Immunogenic -
• Used in lab for serotyping
• Attachment
• Passive transport

Question 3

antimicrobials

Answer 3

antimicrobials

Target for cell-wall synthesis inhibiting microbials*

• Penicillins
• Cephalosporins
• Vancomycin

NOTE: These inhibit transpeptidase enzyme that cross-links the peptide chains

Question 4

2 important genera that form spores

Answer 4

2 important genera that form spores are:

• Bacillus
• Clostridium

Wounds contaminated with soil can be infected with spores and cause:

• Tetanus
• Gas gangrene

NOTE:

Highly resistant to heating

• spores not killed by boiling (100º C)
• killed at 121° C under pressure (autoclave)
• Highly resistant to chemicals
• Including most disinfectants
• Attributed to keratin-like coat of spore

Question 5

What two toxic molecules are generated by bacteria? What are their mechanism of action to deal with them?

Answer 5

Dealing with toxic oxygen species

When oxygen is used for generation of energy, 2 toxic molecules are generated:

• Superoxide radical O₂-
• Hydrogen peroxide H₂O₂

In order to deal with these toxic radicals, bacteria that utilize O2 usually produce the following 2 enzymes:

–Superoxide dismutase *

2O₂- + 2H+ → H₂O₂ + O₂

–Catalase *

•2H2O2 → 2H2O + O2

Question 6

Obligate aerobes characteristic and examples

Answer 6

Obligate aerobes

Characteristics

• Require oxygen
• Have no fermentation pathways
• Generally produce superoxide dismutase

Important genera

• Mycobacterium*
• Pseudomonas

Question 7

Microaerophiles

Answer 7

Microaerophiles

Examples of Microaerophiles

• Campylobacter*
• Helicobacter*

Note:

• Microaerophiles Require lesser amounts of O₂
• 5-10%

Question 8

Facultative anaerobes

Answer 8

Facultative anaerobes

• Most bacteria are Facultative anaerobes
• eg. Enterobacteriaceae*

Note:

• Respire aerobically until oxygen is depleted
• They use fermentation or anaerobic respiration

NOTE: A facultative anaerobe is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation or anaerobic respiration if oxygen is absent

Question 9

Obligate anaerobes

Answer 9

Obligate anaerobes

Examples of Obligate anaerobes

• Clostridium*
• Bacteroides*
• Actinomyces *

Note: Characteristics

• Lack superoxide dismutase
• Generally lack catalase
• Are fermenters
• Cannot use O₂ as terminal electron acceptor