Flashcards in ID and Antimicrobial Therapy Deck (38):
What might cause a falsely positive fever?
-drug induced: beta lactam abx (penicillins and cephalosporins) or phenytoin
What might result in a falsely negative fever?
What is the normal WBC count?
What is a left shift?
increased WBC with increase in immature neutrophils (bands)
How high might WBC be in a bacterial infection?
What do immature bands indicate?
increased bone marrow response to infection
What do bands > 10% indicate?
erythrocyte sedimentation rate
(how far RBCs fall in 1 hour)
1.0-1.5 moderate inflammation
> 10 suggests infection
-biomarker that becomes elevated during bacterial infection
-appears to reflect the severity of infection
-crystal violet stain
-add iodine to enhance stain
What is the difference between gram + and gram - bacteria? How do they stain?
-Gram +: thicker cell wall w/ lots of peptidoglycans; purple
-Gram -: thinner cell wall w/ more lipids, fewer peptidoglycans; pink
What bacteria stain with acid-fast staining?
What are gram stains routinely performed for (eg what types of infections)?
-CSF for meningitis
-urethral smears for STIs
-abscesses or effusions
What is the gold standard for diagnosis and treatment of infections?
Antibody and Antigen Detection
-detection and quantification of antibodies directed against a specific pathogen or its components
How can anthrax be diagnosed?
kills sensitive organisms
inhibits bacteria growth but does not kill them
What is meant by antimicrobial spectrum of activity?
-narrow: kills small # of narrow range of bacteria
-broad: kills many different kinds of bacteria
Minimum Inhibitory Concentration
MIC = the lowest antimicrobial concentration that prevents visible growth of an organism after 24 hours of incubation
Susceptibility Testing: MAcrodilution Method
-mix pathogen w/ serial dilutions of antibiotic
-incubate over night
-1st clear tube is MIC
Susceptibility Testing: MIcrodilution Method
-serial dilutions of several abx in a 96 well plate
Susceptibility Testing: Kirby Bauer Disk Method
-paper discs impregnated with various abxs are placed on agar plate seeded with lawn of bacteria
-zone of growth inhibition around the discs is related to MIC (sensitivity and susceptibility)
Susceptibility Testing: The E-test
-strip with various concentrations of abx placed on agar plate of bacteria
-as [abx] increases, bacterial growth is affected more
Susceptibility Testing: What are the automated methods?
-Vitek system: photometric assessment of turbidity
-Microscan system: fluorogenic substrate hydrolysis as indicator of bacterial growth
How are the peak serum concentration and MIC related?
peak serum concentration should be 2-4x MIC for the bacteria to be susceptible
What factors increase abx resistance?
-low dose, inadequate levels
-abx in animal feed??
What must an antibiotic be able to do in order to have antimicrobial activity?
-reach target: cell wall, nucleus, ribosomes
Name 4 methods of resistance.
-altered target (eg penicillin binding proteins on cell surface)
-gram - have porin channels in cell walls that abx use to enter
-bacteria will close or reduce # of porin channels
-the club bouncer
-abx gets in, but is identified as shady impostor and gets kicked out
abx gets into cell, but is inactivated (usually by enzymes like beta-lactamase)
-example: macrolide abx gets in and normally works at ribosome; bacteria methylates its ribosomes to block abx activity
-example: bacteria alters penicillin binding proteins to block action of penicillins and cephalosporins
Concentration Dependent Killing Rate
-more bacteria killed at higher [ ] of abx
-some aminoglycosides and FQs exhibit CDKR
-penicillins and other beta-lactams usually do not show CDKR
-persistent effect of an abx on bacterial growth after the abx is removed from a bacterial culture
-most bactericidal abx exhibit PAE against susceptible pathogens
What is an advantage of post-antibiotic effect?
allows for less frequent dosing