Lecture 4 Flashcards
Culture medias
Selective = favor growth Differential = Visually distinguish
Selective Media
Additives toxic to some bacteria
MacConkey Enteric Media= Prevent growth of gram positive bacteria
Differential Media
Differentiate between species based on their appearance on media
Blood Agar Media
Shows differences
Hemolytic(produce hemolysin and destroys RBC) vs non-hemolytic
Culture Based Diagnostic
Collect , Grow, Identify
Antibiotics
Supress or kill bacteria (not fungi or antivirals)
Sources of Antibiotics
Soil
Synthetic
Semi synthetic (modified)
Selective Toxicity
Kill bacteria without harming host
Therapeutic Index (T.I)
= Toxic Dose (to human) / Therapeutic dose (Kills bacteria)
The larger the dose the safer the drug
Spectrum of Activity
Narrow = Few Broad = Many
No drug can be effective against all species of bacteria
Bactericidal
Kills bacteria
Bacteriostatic
Inhibits growth
Quinolones (prokaryotic)
Inactivates DNA gyrase (no super coiling = no dna replication)
Rifampin (prokaryotic)
Binds to RNA polymerase = Blocks messenger RNA synthesis
Block Protein Synthesis
Bind to the bacterial ribosome to interference with protein synthesis
Eukaryotic cells have different ribosome
Inhibition of Metabolic Pathways
Sulfonamide (and Sulfa drugs)
Blocks synthesis of bacterial folic
Similar to PABA, but doesn’t create folic acid
Euc = Get PABA from diet
Disrupt Bacterial Cell Membranes
Polymyxins - Bind to Phospholipids and becomes part of membrane
Result in loss of membrane function
Last resort due to not being selectively toxic
Usually an external cream
Block Peptidoglycan synthesis
Large and diverse group of AB
High Selective toxicity because PG is unique to bacteria
Lactams=
Interfere with enzymes required for PG = Lysis of walls
Requires cell is be active
AB in Combo
Avoid Antagonism = Drug blockage
Achieve synergism = Enhanced effect (attack different pathways)
Costly
Reaction to AB use
- Toxicity
- Allergic reactions (rare), more intolerance
- Disruption of normal flora
Super Infection
Overgrowth of drug-resistant bacteria
Clostridium Difficle (resistant to AB) = Causes bacteria
