Antimicrobial Drugs (Quiz 9/11/15) Flashcards
Define Bacteriostatic and give examples
Inhibits the growth of bacteria
Ex. Tetracycline, sulfonamides, chloramphenicol
Define Bactericidal and give examples
Rapidly kills the target organism
Ex. Penicillin, streptomycin, cephalosporins, polymyxin, and neomycin
Define MIC (mean inhibitory concentration)
The minimum concentration of a drug necessary to inhibit the growth of an organism
Define Breakpoints
Known MIC (mean inhibitory concentration) values that have been determined for a given antimicrobial for a given pathogen in a given animal species
Define MBC (mean bactericidal concentration)
Gives an indication of the usefulness of antimicrobials that are bactericidal
Define the “spectrum” of an antimicrobial
How wide a variety of bacterial are affected by that agent
Which type of antimicrobials work by inhibiting growth by analoques?
Sulfonamides
What is the analoque being inhibited by sulfonamides and how is it being inhibited?
PABA (para aminobenzoic acid)
Sulfa drugs are analoques of PABA and compete with it for folic acid - in sufficient concentrations, the sulfa drug will inhibit the folic acid synthesis pathway and prevent the growth of bacteria
What is the role of PABA?
PABA is used to form folic acid, a necessity to the synthesis of purines
What are two of the cons associated with sulfonamides?
- Have a problem with solubility
2. Some are known to precipitate in the kidneys
Are sulfonamides banned from use in food animals?
Yes, for the most part
What are sulfonamides typically given in combination with?
Trimethoprim
How does trimethoprim act? What does it act on?
Inhibits the same folic acid synthesis pathway that sulfonamides do; however, it acts on dihydrofolate reductase
Which types of antimicrobials inhibit cell wall synthesis?
Beta lactams (penicillins) Semisynthetic penicillins Bacitracin Vancomycin Cephalosporins
True or false: all penicillins contain the beta lactam ring structure?
True
What does the penicillin bind to in the cell wall?
Transpeptidase enzymes
Explain the effects transpeptidases binding penicillin has on the organism.
- Binding is irreversible, so the transpeptidase enzymes are thus inactivated
- Cross-bridging can NOT occur
- Peptidoglycan layer weakens
- Bacterium bursts
Which type of organisms is penicillin active against?
Mostly active against gram (+)
Less active against gram (-)
What are some examples of semisynthetic penicillins?
Amoxicillin
What is the difference between penicillins and semisynthetic penicillins?
Semisynthetic penicillins have a greater ability to withstand stomach acid, which means they can be given orally and they have a longer activity. Some are also resistance to breakdown by the penicillinase enzyme.
Clavamox is a combination of amoxicillin and clavulanic acid. What role does the clavulanic acid play?
Clavulanic acids have a beta lactam ring that binds penicillinase enzymes, preventing them from destroying the active beta lactam ring of the amoxicillin.
What are the three advantages to Cephalosporins? (Extra credit - what is a fourth advantage?)
- Resistant to penicillinase
- Not as allergenic as penicillin
- Have a broad spectrum of activity
- (Extra) Longer plasma half-life in third generation
What are third generation Cephalosporins active against?
Most effective against gram (-)
What is a common drug that is an example of a Cephalosporin?
Convenia
Bacitracin is isolated from what organim?
Bacillus subtilis
What is Bacitracin affective against?
Gram (+)
Is Bacitracin bacteriostatic or bactericidal?
Bactericidal
Which types of antimicrobials are inhibitors of the cell membrane?
Polymyxins
Polyenes
Which polymyxins are in use?
B and E
Explain the action of polymyxins.
Polymyxins bind to the outer surface of cell membranes and disrupt the structure and function of the phospholipid and lipopolysaccharide components.
What types of bacteria are polymyxins active against?
Gram (-)
What are polyenes used to treat?
Fungal infections
What are two polyene agents that are typically in use?
Amphoteracin B
Nystatin
Which types of antimicrobials are inhibitors of DNA synthesis?
Quinolones
Fluoroquinolones
Metronidazole
Novobiocin
What type of DNA synthesis do Quinolones inhibit?
DNA gyrase A
True or false: fluoroquinolones are banned from use in food-producing animals.
True
What is Metranidazole effective against?
Anaerobic bacteria
Protozoa
Is Novobiocin bacteriostatic or bactericidal?
Bactericidal
What type of DNA synthesis does Novobiocin inhibit?
DNA gyrase B
Which drug inhibits transcription?
Rifampin
What is Rifampin effective against?
Gram (+)
Mycobacterium
Rhodococcus equie
What is Rifampin’s mechanism of action?
Selectively inhibits DNA-dependent RNA polymerase of bacteria
Which types of antimicrobials are inhibitors of the 30S ribosomal subunit and inhibit translation?
Tetracycline
Doxycycline
Nitrofurans
How does Doxycycline differ from Tetracycline?
Doxycycline is more lipophilic and more easily absorbed from the intestinal tract
Tetracycline is easily deposited into calcified tissue
What type of infection are Nitrofurans commonly used to treat?
Urinary tract infection
Which type of antimicrobials are inhibitors of translation through the 50S ribosomal subunit?
Chloramphenicol
Florfenicol
Macrolides: erythromycin & lincomycin
Long acting macrolides: tilmicosin
Which type of drug is an inhibitor of protein assembly?
Griseofulvin
Griseofulvin is a drug commonly used for the treatment of what type of infection?
Dermatophyte (roundworm) infection
Griseofulvin specifically targets what?
Fungi that have chitin in their cell walls
Is Chloramphenicol bacteriostatic or bactericidal?
Bacteriostatic
Is Chloramphenicol allowed for use in food animal species?
NO!
Why can Macrolides NOT be combined?
Macorlides attach to the same site on the 50S ribosomal subunit as Chloramphenicol. Only molecule of antibiotic can bind per ribosomes, so combined, these drugs would compete for the same sites.
