Lecture 4: Antibiotics Flashcards
(48 cards)
define the term antibiotic
sustance produces by a microorgansim that is effective in killing or inhibiting growth of other microorganisms
define the term antimicrobial agent
any synthetic drug used to treat and infectious disease
- antibacterial
- antifungal
- antiprotozoal
- antiviral
what is an organic antibiotic
isolated from bacteria or fungi (penicillin, erythromycin)
whats a semi-synthetic antibiotic?
derived from an organic compound for greater efficacy eg. amoxicillin, methicillin, oxacillin etc. derived from penicillin
what are synthetic antibitoics/antimicrobial drugs
generated in the lab (eg. sulfonamides, quinolones)
List the ideal qualities of an antibiotic
*kill or inhibit growth of pathogens
*cause no damage to the host
*cause no allergic reaction to the host
*be stable for storage as solid or liquid
*remain in specific tissue long enough to be effective
*kill the pathogens before they mutate and become
resistant
why is inhibiton sometimes enough instead of killing? explain what happens
Could be enough to inhibit – infection, organism colanises and proliferateis, immmune system overwhelmed
Substance that stops bacteria from proliferating, immune system can handle those
Bacteriostatic antibitic is good enough
What is the antibacterial spectrum and what are the two features?
range of activity against bacteria eg. broad or narrow
explain the term narrow-spectrum AB
works only against a limited variety of bacteria
e.g. vancomycin (only against Gram-positives)
explain the term broad-spectrum AB
works against a variety of Gram+/- bacteria
e.g. amoxicillin, tetracyclin
define bacteriostatic activity and explain why its useful
level of antimicrobial activity that inhibits growth of organism.
Static useful bc own immune system has upper hand to deal with the bacteria
define bactericidal activity
level of antimicrobial activity that kills organism
what is the purpose of antibiotic combination
combining different antibiotics for:
- broaden the antimicrobial spectrum
- treatment of polymicrobial infections
- prevent emergence of resistant organism
- achieve a synergistic killing effect
define the term anitibiotic antagonism
activity of one antibiotic interferes with activity of other, e.g.
the sum of activity is less then the most active individual drug
(penicillin-chloramphenicol). Like 1+1= <1
define the term antibiotic synergism
antimicrobial activity is higher than the sum of combined drugs
(e.g. penicillin-streptomycin). Like 1+1= >2
what is an antibiogram
result of lab testing for sensitivity of an isolated strain to different antibiotics
What are the three antibiogram methods
- Semi-quantitative based on diffusion (Kirby-Bauer method)
- Quantitative based on dilution series
- Determining the Minimum Bacteriocidal Concentration (MBC)
What is caluclated in the kirby bauer method?
In Kirby-Bauer testing, bacteria are placed on a plate of solid growth medium and wafers of antibiotics (white disks, shown) are added to the plate. After allowing the bacteria to grow overnight, areas of clear media surrounding the disks indicate that the antibiotic inhibits bacterial growth.
What is MIC and what does it tell us?
MIC - minimum inhibitory concentration, calculated for the diamter of AB disk - antibiotic concentration highest at centre of disc and lowest at edges
tells us in vitro levels of susceptibility or resistance of specific bacterial strains to applied antibiotic.
how can MIC be established i.e what methodology
- using agar plates
- using viles
how is MIC established using vials
quantitative based on dilution series
last vial in which no bacteria grow contains antibiotic at Minimum Inhibiotry Concentration
what is it and how is the Minimum Bacteriocidal Concentration determined?
- the lowest concentration of an antibacterial agent required to kill a bacterium over a fixed period under a specific set of conditions
- determined by using different test tubes with different concentrations of antibiotic concentrations and subculturing the clear broth (with no bacterial growth) onto antibiotic free solid media to see wether the AB is bacteriostatic or bacteriocidal (i.e if bacteria will grow on agar or not)
- if it doesnt grow then the tube with the least concentration of AB that killed bacteria is the MBC
what are the different classifications of antibiotics?
- drugs that bloc bacterial cell wall synthesis
- inhibitors of RNA transcription
- inhibitors of nucleic acid synthesis
- antimetabolites
- inhibition of protein synthesis
give some examples of drugs that block bacterial cell wall synthesis
a. ß-lactam antibiotics
b. glycopeptides