Chapter 15
What is the role of IgA proteases?
Destroy IgA antibodies on mucosal surfaces.
Who discovered penicillin and when?
Alexander Fleming, 1928.
What is the mechanism of tetracyclines?
Interfere with attachment of tRNA to ribosome.
What is the Kirby-Bauer test?
Disk diffusion method to assess antibiotic susceptibility.
Felix d'Herelle (1917) and William Twort (1915)
Differentiate exotoxins and endotoxins.
Exotoxins = proteins secreted by bacteria; endotoxins = lipid A of LPS in Gram-negative bacteria.
What organisms produce most antibiotics?
Streptomyces species (filamentous soil bacteria).
What is the mechanism of macrolides?
Prevent translocation of ribosome along mRNA.
What are R factors?
Plasmids that carry antibiotic resistance genes.
What concept did Ehrlich propose?
The concept of a magic bullet and selective toxicity (a drug that kills harmful microbes without damaging the host).
What is the effect of lipid A?
Causes fever, shock, and blood clotting.
What is the mechanism of β-lactam antibiotics?
Inhibit cell wall synthesis by blocking peptidoglycan cross-linking.
What is the mechanism of quinolones?
Inhibit DNA gyrase, blocking replication.
Name two mechanisms of antibiotic resistance.
Enzymatic destruction (e.g., β-lactamase), alteration of target site.
What are antiviral drugs and what do they do?
Name three types of exotoxins. Give examples of those toxins
A-B toxins (e.g., diphtheria), membrane-disrupting toxins (e.g., hemolysins), superantigens (e.g., toxic shock syndrome toxin).
Why are fungal infections hard to treat?
Fungi are eukaryotic, so drugs often harm host cells too.
What is the mechanism of sulfonamides?
Inhibit folic acid synthesis by competing with PABA.
What does the E test do?
Determines the minimal inhibitory concentration (MIC). The lowest antibiotic concentration preventing bacterial growth.
What are some antihelminthic drugs?
Ivermectin. Niclosamide, Praziquantel, Mebendazole and Albendazole
What is antigenic variation?
Pathogens alter surface antigens to evade immune response.
Name two antibiotics that inhibit protein synthesis.
Streptomycin (binds 30S), chloramphenicol (binds 50S).
What is the MIC and MBC?
MIC = minimum inhibitory concentration; MBC = minimum bactericidal concentration.
What are examples of misuse of antibiotics?
- Using outdated or weakened antibiotics
- Using antibiotics for the common cold and other inappropriate conditions
- Using antibiotics in animal feed
- Failing to complete the prescribed regimen
Before the discovery of antibiotics, Streptococcus pyogenes caused how many post-birth deaths?
Half of all post-birth deaths and was a major cause of death from burns