Ecosystem Interactions Class Discussion Presentation in Blue Green Lined Styl...
Antibiotics
1. ANTIBIOTICS
Antibiotics can be defined as substances capable ofkilling & inhibiting
the growthof micro organisms
Mechanismof action
Inhibition of cellwall synthesis Penicillins
Cephalosporins
Monobactams
Vancomycin
Inhibition of DNA gyrase: Quinolones
RNA polymerase Rifampicin
Inhibition of protein synthesis: Aminoglycosides
Tetracyclines
Erythromycin
Chloramphenicol
Inhibition of folic acid metabolism: Trimethoprim
Sulfonamides
Bacteriostatic vs. bactericidal drugs
• Bacteriostatic
– arrest the growth and replication of bacteria
2. – at serum levels achievable in the patient - limit the spread of infection
while the body's immune system attacks, immobilizes, and eliminates
the pathogens.
– If the drug is removed before the immune system has scavenged the
organisms, enough viable organisms may remain to begin a second
cycle of infection.
• Bactericidal
– kill bacteria at drug serum levels achievable in the patient. - often
drugs of choice in seriously ill patients.
• It is possible for ATB to be bacteriostatic for one organism and bactericidal
for another.
Antimicrobial activity
• Antimicrobial activity: the ability that a drug kills or suppresses the growth
of microorganisms.
• Minimum inhibitory concentration(MIC)
– the minimum amount of a drug required to inhibit the growth of
bacteria in vitro.
• Minimum bactericidalconcentration(MBC)
– the minimum amount of a drug required to kill bacteria in vitro
Classificationofantibacterialagents:
bactericidal bacteriostatic
β-lactam agents Erythromycin
Aminoglycosides Tetracyclines
Co-trimoxazole Chloramphenicol
Vancomycin Sulfonamides
3. Chemotherapeutic spectra
Narrow spectrum
only against a single or a limited group of microorganisms,
e.g. INH is active only against mycobacteria.
Broadspectrum
e.g. tetracycline and chloramphenicol
affect a wide variety of microbial species.
!!! alter the normal bacterial flora
precipitate a superinfection of an organism, e.g., candida.
Drug resistance
growth of bacteria is not halted by the maximal level of that antibiotic that can be
tolerated by the host.
Primary
Some organisms are inherently resistant to an antibiotic
e.g., gram-negative organisms are inherently resistant to vancomycin.
Secondary
spontaneous mutation or acquired resistance and selection.
Cross-resistance
resistant to more than one antibiotic.