Module 6: Antimicrobial Agents Flashcards
Define antimicrobial agent
Chemotheraputic agent used for treatment of infectious diseases
What 4 criteria must an antibiotic have in order to be used?
- Selective toxicity (kill bacteria, no damage to host cells)
- Not cause allergic reaction
- Soluble in body fluids and capable of tissue penetration
- Microorganisms must not readily develop resistance
What are broad spectrum antibiotics?
Affect wide variety of bacteria, gram positive and negative
Must have action against some Enterobacteriaceae to be broad
What are narrow spectrum antibiotics?
Affects small group of bacteria
Gram positive OR negative, not both
Define bactericidal
Agent kills bacteria
Define bacteriostatic
Agent prevents bacteria from multiplying, then body defenses get rid of it
Why would a bacteriostatic agent not be used on immunocompromised patients?
There are no body defenses to get rid of the bacteria
What are the 5 possible modes of action an antibiotic may have?
- Inhibit cell wall synthesis
- Inhibit protein synthesis
- Inhibit DNA and RNA synthesis
- Inhibit cell membrane function
- Inhibit other metabolic processes
Why are agents which inhibit the cell wall synthesis of bacteria used? (2)
- Human cells don’t have a cell wall
2. Peptidoglycan in the bacteria cell wall is unique to bacteria
What is the core component of all cell wall synthesis inhibiting antibiotics? What is it made of?
Beta-lactam ring
Made of three carbons and one nitrogen molecules arranged in a ring
What do cell wall synthesis inhibiting antibiotics bind to?
Enzymes in the cell wall called Penicillin binding proteins
How do cell wall synthesis inhibiting antibiotics cause bacterial death?
The agents bind to cell wall enzymes that are the last stage of peptidoglycan synthesis, which inhibits cross-linking between the proteins
This causes weakness and eventual rupturing
Why are gram negative bacteria usually resistant to beta-lactam antibiotics?
They have a lipid layer covering the peptidoglycan layer, protecting it from the antibiotic
What are the 2 major beta-lactam antibiotic groups?
Penicillin and cephalosporins
What are the 4 groups of penicillin?
Natural, beta-lactamase resistant, extended spectrum, anti-pseudomonal
What are natural penicillins?
Penicillin where the original compound is extracted from Penicillium mold
The compound is Penicillin G or Benzylpenicillin
What spectrum does natural penicillin have?
Narrow, gram positive with a few gram negative
Is there bacterial resistance to natural penicillin? If so, how does it work?
Yes, it can be inactivated by bacteria which produces beta-lactamase (enzyme) which opens the beta-lactam ring
What is the clinical usage of natural penicillin?
Penicillin G - injection, resistant to stomach acid
Penicillin V - orally
Usually given with other drugs to improve absorption and retention
What laboratory testing is done in regards to bacterial sensitivity?
Penicillin G used to test and applied to all other natural penicillins EX: Penicillin G is sensitive, so are other penicillins (class concept)
What is class concept?
The test results for sensitivity to one antibiotics applies to all other antibiotics of the same class
How do beta-lactamase resistant penicillins work?
“Bulky” side chain added to protect the beta-lactam ring
What penicillins are included in the beta-lactamase resistant class?
Oxacillin, cloxacillin, dicloxacillin, methicillin
Is there bacteria resistance to beta-lactamase resistant penicillin? If so, how does it work?
Resistance occurs only when the bacteria develops it, by altering their penicillin binding proteins to prevent binding