antibiotics Flashcards
define minimum inhibitory concentration.
minimum amount of antibiotic required to cure infection so there isnt excess in body
what are the 2 major determinants of anti bacterial effects?
- concentration - needs to inhibit lots of receptors
- time - must inhibit receptors for sufficient period of time
what factors affect how antibiotics work so therefore what do we need to consider when administering it?
A function of
Its release from the dosage form;
Its absorption from the site of administration into the bloodstream; - whats the appropriate route of administeration, IV, oral ect
Its distribution to various parts of the body, including the site of action - Which antibiotics will penetrate that site?What is the pH of the site? Is the antibiotic lipid soluble?
Its rate of elimination from the body via metabolism (LIVER) or excretion (KIDNEY) of unchanged drug. - what dosage interval / duration
what are the ways in which bacteria can be antibiotic resistant?
- change antibiotic target
- destroy antibiotic
- prevent antibiotic access
- remove antibiotic bacteria
outline the bacterial mechanism of changing the antibiotic target for antibiotic resistance.
- Bacteria change the molecular configuration of antibiotic binding site or masks it e.g.
- Bacteria changes the molecular configuration of antibiotic binding site or masks it e.g.
Flucloxacillin (or methicillin) is no longer able to bind PBP of Staphylococci – methicillin resistant S. aureus MRSA
Wall components change in enterococci and reduce vancomycin binding – Vancomicin resistant Enterococci VRE
Rifampicin activity reduced by changes to RNA polymerase in MTB – Rifampicin Resistant TB
outline the bacterial mechanism of destroying the antibiotic for antibiotic resistance.
The antibiotic is destroyed or inactivated e.g.
Beta lactam ring of Penicillins and cephalosproins hydrolysed by bacterial enzyme ‘Beta lactamase’ now unable to bind PBP
The antibiotic is destroyed or inactivated e.g.
Beta lactam ring of Penicillins and cephalosproins hydrolysed by bacterial enzyme ‘Beta lactamase’ now unable to bind PBP
Staphylococci produce ‘penicillinase’ so penicillin but not flucloxacillin inactivated
Gram negative bacteria phosphorylate and acetylate aminoglycosides (gentamicin)
outline the bacterial mechanism of preventing antibiotic access for antibiotic resistance.
modify the bacterial membrane porin channel size, numbers and selectivity e.g.
Pseudomonas aeruginosa against imipenem,
Gram negative bacteria against aminoglycosides
outline the bacterial mechanism of remove antibiotic bacteria for antibiotic resistance.
Proteins in bacterial membranes act as an export or efflux pumps - so level of antibiotic is reduced
S. aureus or S. pneumoniae resistance to fluoroquinolones
Enterobacteriacae resistance to tetracylines
what are the 2 ways in which bacteria develops antibiotic resistance?
intrinsic = naturally resistant
aquired = spontaneous gene mutation or horizontal gene transfer
horizontal gene transfer from:
- conjugation - sharing of extra chromosomal dna plasmids “bacteria sex”
- transduction - insertion of dna by bacteriophages
- transformation - picking up naked dna
Intrinsic resistance
All subpopulations of a species will be equally resistant
examples
Aerobic bacteria are unable to reduce metronidazole to its active form
Anaerobic bacteria lack oxidative metabolism required to uptake aminoglycosides
Vancomycin cannot penetrate outer membrane of Gram negative bacteria
The PBP in enterococci are not effectively bound by the cephalosporins
name important gram positive resistant bacteria.
MRSA
VRE
name important gram negative
resistant bacteria.
ESBL
Carbapenem Resistant Enterobacteriaceae
explain the process of bacterial replicatin.
Bacteria replicate primarily by binary fission, a form of asexual reproduction:
DNA Replication:
Circular chromosome is duplicated, beginning at the origin of replication.
Cell Elongation:
Cell enlarges and components are evenly distributed.
Septum Formation:
Plasma membrane and cell wall invaginate, dividing the cell into two.
Separation:
Two genetically identical daughter cells are formed.
Horizontal Gene Transfer: Contributes to genetic diversity:
Transformation: Uptake of free DNA from the environment.
Conjugation: Transfer of plasmids via a pilus.
Transduction: Gene transfer by bacteriophages.
Factors Influencing Bacteriostatic vs. Bactericidal Activity
Concentration: Some antibiotics (e.g., chloramphenicol) can be bacteriostatic at low concentrations but bactericidal at higher concentrations.
Bacterial Species: Antibiotic action depends on the target pathogen (e.g., penicillin is bactericidal for Streptococcus but not for Enterococcus).
Site of Infection: Immune response at the infection site influences the effectiveness of bacteriostatic agents.
