12 - antibiotics Flashcards
what are antibiotics?
natural or synthetic compounds that prevent microorganism growth or cause lysis
anti life - stops life
whats the difference between viable and total population?
viable = able to reproduce
total = actual population
what are the 3 different kinds of antibiotics?
bacteriostatic
bacteriocidal
bacteriolytic
what is bacteriostatic?
stationary (no increase)
total and viable cell count remain constant
prevents replication, used to stabilise the population and control the infection
what is bacteriocidal?
to die
total cell count stays same but viable cell count decreases
used for invasive and aggressive infections
what is bacteriolytic?
to lyse/burst
both total and viable cell count decrease
interferes with structural integrity
very strong antibiotics but hugely affect the microbiota
what is MIC?
minimum inhibitory concentration
the minimum antibiotic to inhibit growth
MIC susceptibility testing
sensitive
intermediate
breakpoint
resistant
MIC susceptibility testing - SENSITIVE
appropriate dosage of standard agent
S = routine prescription
MIC susceptibility testing - INTERMEDIATE
MIC higher than sensitive
equals the concentration the drug reaches in patient
I = in-vivo and in-vivo concentration
MIC susceptibility testing - BREAKPOINT
concentration of drug attainable in serum
B = limit of therapeutic success
MIC susceptibility testing - RESISTANT
isolate unaffected by safe concentration of drug
drug would harm patient at a higher dose
MIC variables
- media
- pH
- temperature
- oxygen level
- population density
what are breakpoints?
discriminatory antimicrobial concentrations used in the interpretation of results of susceptibility testing to define isolates as susceptible, intermediate or resistant
targets in the bacterial cell
- inhibition of cell wall synthesis
- inhibition of replication, transcription and translation
- inhibition of synthesis of essential metabolites
- membrane integrity lesions
major classes of protein synthesis-inhibiting antibacterials
chloramphenicol, macrocodes and lincosamides
aminoglycosides
tetracyclines
what do chloramphenicol, macrocodes and lincosamides do?
- bind to the 50S ribosomal subunit
- prevent peptide bond formation
- stop protein synthesis
what do aminoglycosides do?
- bind to the 30S ribosomal subunit
* impair proofreading, resulting in production of faulty proteins
what do tetracyclines do?
- bind to the 30S ribosomal subunit
* block the binding of tRNAs inhibiting protein synthesis
how do antibiotics affect microbial metabolism?
target essential biochemical pathway anti-metabolites
stop the pathway or generate a toxic intermediate
how do antibiotics target DNA?
target replication or DNA packing
prevent chromosomal replication (e.g.. DNA gyrase inhibition)
examples:
• quinolones - broad range as Gyrase found in all bacteria
• ciprofloxacin - used in UTI treatment but also bacteremia
how do antibiotics break the cell wall?
target cell wall synthesis or integrity
causes the cells to lyse
examples:
• penicillins - beta-lactam antibiotics, bind to PG synthesis machinery, useful for both gram +ive and -ive infections
• vancomycin - binds to PG precursors
mechanisms of resistance to antibiotics in bacteria
- reduced permeability
- inactivation of antibiotic
- alteration of target
- development of resistant biochemical pathway
- efflux - pumping out
last resort antibiotics
antimicrobial resistance and healthcare associated infections (AMRHAI) is part of Public Health England’s
bacteria reference department (BRD)
AMRHAI = 7 sections: • staphylococcus reference • opportunist pathogens • antibiotic susceptibility testing • resistance mechanisms section • infection prevention and control • bacterial identification services (BIDS) • antimicrobial resistance in STIs
