Hasset Exam

• 1. Peptidoglycan inhibition. 
• 2. Protein synthesis inhibition.
• 3. DNA replication inhibition.
• 4. Folic Acid synthesis inhibition.
• 5. Lipid biosynthesis inhibition.

Beta-Lactam antibiotic

Inhibits transpeptidases, the enzymes that catalyze the final cross-linking step in synthesis of peptidoglycan.

Aminoglycoside

Binds irreversibly to the 30S subunit of bacterial ribosomes, and block the initiation of protein synthesis.

Quinolone

Inhibits DNA replication by attacking bacterial DNA gyrase or topoisomerase 4.

Antimetabolites

Compete with para-aminobenzoic acid (PABA), thereby preventing the synthesis of the folic acid required by certain micororganisms.

A selectively inhibiting antibiotic that acts agains cellular lipid biosynthesis.

B-lactam antibiotica. Inhibit transpeptidases (PBPs), the enzymes that catalyze the final crosslinkingstep in the synthesis of peptidoglycan

bacitracina. Interferes with dephosphorylation of lipid carrier responsible for movingpeptidoglycan subunit across cell membrane.

Glycopeptides. Inhibits cell wall synthesis by sterically interfering with formation of bridgesbetween peptidoglycan chains.

Isoniazid. Inhibit biosynthesis of cell wall mycolic acids, thereby making themycobacteria susceptible to reactive oxygen radicals and otherenvironmental factors.

- hydrolysis of the antibiotic by β -lactamases (both gram positive and gramnegative)

- fails to bind to PBPs (both gram positive and gram negative)

- fails to cross membrane (only gram negative organisms)

There are two genes of interest in this type of resistance.

1. VanS:likely senses vancomycin in the environment.

• 2. VanR: when phosphorylated by VanS, activates transcription of othergenes, the organism synthesizes depsipeptides made by vanA. Whenthese peptides added to the building peptidoglycan moiety, bindglycopeptide antibiotics with decreased efficiency
•      a)VanH, A,X,Y

- Isoniazid believed to inhibit biosynthesis of cell wall mycolic acids, therebymaking the mycobacteria susceptible to reactive oxygen radicals and otherenvironmental factors.

- Activation of INH requires the enzyme catalase-peroxidase (KatG) and anelectron sink (hydrogen peroxide)

- KatG is the only enzyme capable of activating INH and therefore KatGmutant strains of M. tuberculosis are INH resistant

- However, KatG is not the only “player” involved in INH susceptibility orresistance. Depicted on the next page is a schematic diagram of other M.tuberculosis factors that are involved in resistance/susceptibility to INH.

Bactericidal: kill bacteria directly

Bacteriostatic: Prevent bacteria from growing

the lowest concentration of an antimicrobial that will inhibit the visible growth of a microorganism after overnight incubation.

Alters bacterial cell membranes.

Aminoglycosides

Chloramphenicol

Tetracyclines

Marcolides

Lincosamides

1. Efflux of drug : drugs is rapidly expelled from resistant cells.

2. Ribosomal protection: No binding of tetracycline to ribosome because ribosome structure has been modified.

a. Quinolones

i. Target1.DNA gyrase or topoisomerase IV

• ii. Resistance
•      1. Nosocomially-derived resistant isolates have acquired resistance viadecreased permeability.
•      2.Mutations in genes encoding DNA gyrase

b. Rifampin

i. Target1. DNA-dependent RNA polymerase

• ii. Resistance
•      1. Mutation in the chromosomal

a. These antimetabolites that interfere with normal synthesis or function of ametabolite in the cell.

b. Sulfonamides

a. It inhibits FAS2 II machinery.

     i.Fab F/B are elongation condensing enzymes which are essential components

a. Faster metabolic rate

b.Rapid generation time

c.More versatile in use of energy sources and use of alternative electron acceptors.

d.More Diversity wiht respect to completeness of their biosynthetic pathways.

e.Streamlined methods of assembly

•      i.DNA replication
•      ii.RNA transcription
•      iii.Protein translation

f.Unique materials (eg. LPS, merein, toxins, pigments)

a.Lag phase

b.Exponential phase

c.Stationary phase

d.Death phase

a. Aerobic respiration allows organisms to proliferate in the presence of oxygen;however, cells must have enzymes to deal with reactive oxygen species.

a.Passive diffusion

b.Facilitated diffution

c.Active transport

d.Group translocation

     i.differs from active transport in that substrate appears inside the cell in achemically modified form (eg. phosphate addition)

Temperature

pH

a.Regulation

     i.Produce siderophores to scavenge iron

b.Major players

•      i.Lactoferrin
•      ii.Transferrin
•      iii.Ferritin
•      iv.Hemin

• a.Chemotaxis
•      i.Positive-in direction of nutrients (Swiming)

     ii.Negative-in opposite direction of repellants (tumbling)

• b.Twitching mobility
•      i.Pillus mediated movement

a.Formation of a genetic time capsle that can survive until conditions are correct, thenit can be triggered to germinate into the parent organism.

a.Feedback inhibition

     i.Mechanism by which biosynthetic and catabolic pathways regulate themselves.

b.Attentuation

     i.The effective regulation of the biosynthesis of amino acids is of vitalimportance to the cell.

• c.Repression
•      
•      i.Down regulates genes

a.Geobacter bacteria growing on anode an metabolize acetate and produce H2 gaswhich can be harnessed for fuel.