ID ch 34 antimicrobial agents

class on march 31st, up to slide 24

specificity def + formula

how well does my new test identify infected individuals, vertically down, how many are positive in both gold standard and new test / total positive by gold standard

what is usually used as a gold standard for TB tests

liquid culture

specificity def + formula

how well does my new test identify uninfected individuals, vertically down, how many are negative in both gold standard and new test / total negative by gold standard

PPV long, expl + formula

Positive Predictive Value: if the test is positive, what is the likelihood that the patient is indeed infected; positive from both gold standard and new test / total positive from new test

NPV long, expl + formula

negative predictive value, if the test is negative, what is the likelihood that the patient is indeed uninfected; negative from both gold standard and new test / total negative from new test

prevalence formula

amount infected / whole population

what can you learn from the same test but in a new cohort

prevalence in population really can impact PPV - if prevalence is smaller, tests become less accurate

4 main antimicrobials

antibacterials, antivirals, antifungals, antiparasitics

3 main mechanisms of antimicrobial resistance

altered target site, altered uptake/efflux, drug inactivation

3 main mechanisms of antimicrobial resistance spreading

Horizontal gene transfer:
chromosome mediated resistance: mutant selection, plasmid-mediated resistance: spread of resistance plasmid, plasmid-mediated resistance on a transposon: spread of resistance gene

antibiotics: what is it, what does it do, where does it go (route of administration!!) - general, just what would be possible answers of these questions

chemical structure (natural or synthetic product), target site/mechanism of action, absorption/distribution/metabolism/excretion of the drug in the body of the host

antibiotics: when is it used, what are the limitations to its use, how much does it cost- general, just what would be possible answers of these questions

spectrum of activity and important clinical uses, toxicity to the human host- lack of toxicity (ie resistance of bacteria), great variation between agents- cost is a huge limiting factor in resource poor settings

target sites for attack for antibiotics (5)

cell wall synthesis, protein synthesis, nucleic acid synthesis, metabolic pathways, cell membrane function

target sites for attack for antibiotics: cell wall synthesis, 3 stages +descr

extracellular stage: translocation of the monomer across the membrane, polymerization and cross-linking to extend the peptidoglycan network
membrane associated stage: attachment of precursors to the lipid carrier C55 and formation of the peptidoglycan monomer
cytoplasmic stage: synthesis of UDP-NAG and UDP-NAM recursors

what cell wall synthesis process can we interfere with specifically (4)

adding cycloserine to interfere with adding of alanines, can prevent dephosphorylation of phospholipid carrier with a bacitracin (C55 lipid), can have a glycopeptide sit on the alanine residues not allowing them to be incorporated, beta lactams which bind to and inhibit enzymes which catalyse the pentaglycine cross-links

stages of cell wall synthesis and when each type of antibacterial can work

cytoplasm (synthesis of cell wall precursors): cycloserine
cytoplasmic membrane (synthesis of new cell wall subunit attached to lipid carrier): glycopeptide, bacitracin
cell wall (attachment of new wall unit to growing peptidoglycan): beta lactams