Antibiotics Flashcards
Antibiotics
chemical compounds synthesized by one microbe that kill or inhibit the growth of other microbial species
Another name for antibiotics:
“magic bullet”
An antimicrobial drug has _________ __________ if it kills microbial cells, but does not kill host cells.
selective toxicity
–cidal
kills microbes directly
–static
prevents microbes from growing
broad spectrum
effective against wide range of species, including both gram negative and gram positive species
example of a broad spectrum antibiotic
tetracycline
narrow spectrum
only active against select species
example of a narrow spectrum antibiotic
penicillin G
What are gram negative more resistant?
outer membrane of gram negative species inhibits the passage of many antiobiotics
Superinfection
Ab tx, especially broad-spectrum, may destroy normal flora
What happens in times of superinfection?
Ab resistant microbes (Candida albicans) can grow unchecked
4 Mechanisms of Action Ab’s use
- Inhibition of cell wall synthesis
- Inhibition of protein synthesis
- Inhibition of nucleic acid replication and transcription
- Inhibition of essential metabolite synthesis
Natural penicillin
Narrow spectrum of range; susceptible to penicillinase
What type of bacteria is penicillin effective against and why?
gram (+) - interferes with cross-linking of peptidoglycan
Semi-synthetic penicillin
extended spectrum and/or resistance to penicillinase
Penicillinase
a beta-lactamase enzyme effective against penicillin
How does penicillinase work?
cleaves beta-lactam ring
4 features of Colistin
- disrupts outer membrane of gram negative cell wall
- disrupts plasma membrane
- cell lysis
- last resort due to nephrotoxicity
2 Mycobacterium species
leprosy and TB
Isoniazid
inhibits mycolic acid synthesis
ethambutol
inhibits corporation of mycolic acid
3 things that inhibit replication?
ciproflaxin, nalidixic acid, UTIs
What does Rifamycin do?
inhibit transcription by selectively binding to the bacterial RNA polymerase
chloramphenicol
binds to 50S portion and inhibits formation of peptide bond
streptomycin
changes shape of 30S portion causing code on mRNA to be read incorrectly
tetracycline
interfere with attachment of tRNA to mRNA-ribosome complex?
Chloramphenicol, Streptomycin, and Tetracycline inhibit what?
Protein synthesis
An inhibitor of metabolic enzymes
sulfonamides
Sulfonamides are ________ inhibitors. They inhibit ____ ____ _____. They are a ________ _________ antibiotic.
competitive; folic acid synthesis; broad spectrum
Erythromycin inhibits translation. Why does erythromycin have a spectrum of activity limited largely to gram positive bacteria?
The gram-negative cell wall blocks erythromycin.
Primary sterol in fungal membranes
ergosterol
primary sterol in animal membranes
cholesterol
Examples of antifungals that target ergosterol synthesis:
Azoles like miconazole and triazole
Flucytosine
cytosine analog interferes with RNA synthesis
Griseofulvin
inhibits microtubule formation
MIC
minimal inhibitory concentration
MBC
minimal bactericidal concentration
2 ways to measure susceptibility of drug:
Disk Diffusion Method (Kirby-Bauer Test) & Broth dilution
Synergism
occurs when the effect of two drugs together is greater than the effect of either alone
Antagonism
occurs when the effect of two drugs together is less than the effect of either alone
4 Mechanisms of Ab Resistance
- blocking entry
- inactivation by enzymes
- alteration of target molecules
- efflux of antibiotic
MDR Pump
Multi-drug resistance; can export many kinds of Abs
Amphotericin B
binds to ergosterol and forms pores in membrane; cytotoxic, generally used only for severe systemic infections
2 ways in which bacteria acquire Ab resistane?
- Mutation during DNA replication
2. Horizontal transfer
Horizontal Transfer
resistance genes are often on plasmids or transposons that can be transferred between bacteria
Problems with Antivirals
Difficult to find because there are few targets you can use (selective toxicity issues)
Amantadine
inhibits viral uncoating (preventing entry of virus into host cell)
Zanamavir
blocks neurominidase (the spikes on the outside of viruses; this prevents them from being released)
Acyclovir
analog of guanosine that has no 3’ OH. The chain terminates thus blocking DNA synthesis (including yours)
Ribavirin
Lowers fidelity of RNA polymerase,
AZT (azidothymidine)
nucleoside analog reverse transcriptase inhibitor
interferons
normal host proteins that prevent spread of viruses to new cells
alpha interferon
used to tread viral hepatitis
imiquimod
promotes interferon production
