Antimicrobial Chemotherapy Flashcards
What is meant if an organism is termed sensitive?
organism is sensitive if it is inhibited or killed by the antimicrobial
What is meant if an organism is termed resistat?
organism is resistant if it is not killed or inhibited by the antimicrobial available at the site of infection.
What are antibiotics active against?
Bacteria
What is meant by a Bactericidal?
antimicrobial that kills bacteria.
What is mean by a Bacteriostatic?
Antimicrobial that inhibits growth of bacteria.
what is meant by MIC?
Minimal inhibitory concentration minimum concentration of antimicrobial needed to inhibit growth of a given
How can antiobiotics be administrated?
Topical
Systemic
Parenteral
How is an antibiotic administered topically?
Applied to a surface (skin or to mucous membranes )
How is an antibiotic administrated systematically?
Taken internally, (orally or parenterally)
Hpw is an antibiotic administered Parenterally?
Administered intra-venously (i.v.) or intra-muscularly (i.m.), occasionally subcutaneously.
What do antibiotics do to bacteria?
By inhibiting or killing bacteria.
Name the three areas of metabolic activity of antibiotics.
Inhibition of cell wall synthesis
Inhibition of protein synthesis
Inhibition of nucleic acid aynthesis.
Why are human cells not affacted by antibiotics?
Human cells do not have cell walls, so they are not affected by antibiotics that inhibit cell wall synthesis
Name two Bactericidal antibiotics which are effective against gram positive bacteria.
Penicillins and Cephalosporins (β-lactams).
Macrolides are considered either bactericidal orbacteriostatic antibiotics. depending on what?
Depending on concentration and bacterial species,
Oxazolidinones are considered either bactericidal orbacteriostatic antibiotics. depending on what?
Depedning on the bacteria being treated.
Measurement of the antibiotic sensitivity of an organism in the laboratory is designed to do what?
Predict whether an infection will respond to treatment with that antibiotic.
In some cases, all strains of a given species are naturally resistant to an antibiotic.
What are streptococci always resitant to?
aminoglycosides
Gram negative organims are always resistant to??
Why?
Vancomycin
Usually due to inability of the drug
to penetrate the bacterial cell wall to exert its action)
If a bacertia is known to be resitant, what becomes irrelevant.
Laboratory Sensitivity Testing
What is aquired resistance?
Resistance may be present in some strains of bacteria but not in others.
Laboratory sensitivity testing is ued to?
Esablish the sensitivity of any bacteria isolate from a patient
What does the widespread use of antibiotics encourage and cause?
causes selective pressure and encourages new resistant organisms to outgrow sensitive strains.
How is resistance aquired?
Spontaneous mutation
Spread of resistance.
Describe how spontaneous mutaion relate to resistance.
Change in structure or function which no longer allows the antibiotic to act
(target may have changed).
How is spread of resistance related to resistance?
the gene/s that code for resistance can spread from organism to organism or from species to species.
How can genes be carried?
Genes can be carried on plasmids (extra chromosomal packages of DNA)
or on transposons (packets of DNA which insert themselves into the chromosome).
How can new genes be aquired?
Horizontal gene transfer
What happens in conjuguation relating to bacteria?
DNA transfer bacteria cells.
What happens in trandsuction relating to bacteria?
Bacterial DNA transferred by viruses.
What happens in transformation relating to bacteria?
naked DNA upttake by bacteria.
What are some issues with antibiotic resistance?
For virtually every antibiotic or antibiotic class,
micro-organisms have evolved a resistance mechanism.
β-lactamase production.
How does β-lactamase production cause issues with antibiotic resistance?
β−lactamases are bacterial enzymes which cleave the
β–lactam ring of the antibiotic and thus render it inactive.
β-lactamases are also common in Gram-negative bacilli.
How can we combat β-lactamase?
1:
To modify the antibiotic side chain producing
new antibiotic resistant to the actions of β-lactamase.
-> for example, co-amoxiclav:
amoxicillin plus the β-lactamase inhibitor clavulanic acid.
To introduce a second component to the antibiotic
(β-lactamase inhibitor) protecting the antibiotic from enzymatic degradation.
-> for example, Flucloxacillin:
(antistaphylococcal) which is a modified form of penicillin.
What are ESBLs?
enzymes that mediate resistance to extended-spectrum
(third generation) cephalosporins.
What is Antibiotic resistance transferred by?
Conjugation (plasmids0.
Name some gram positive cocci.
Streptococcus
Pneumococcus
Enterococcus
Name some gram negative cocci
Neisseria
Morasella
Name a gram positive bacilli.
Corynebacterium
Clostridium
Name some gram negative bacilli.
Escherichia coli
Shingella
Salmonella
Name some gram negative spirals.
Vibrio cholerae
Helicobacter pylori
What antibiotic are most gram negative organisms resistant to?
Benzyl penicillin
How can you disrupt peptidoglycan synthesis
Inhibiting the enzymes (penicillin-binding proteins, PBPs) responsible for cross-linking the carbohydrate chains.
Most hospital strains of which kind of bacteria produce β-lactamase?
Staphylococcus aureus
