Ast Flashcards
What Abiotics cannot be used on the pediatric population
-there are age limitations
Fluoroquinolones: impair cartilage development
Teracycline : impair teeth development
need to always consider oral vs intravenous antibiotics (out or in pt)
which antibiotic’s are made or not made for specific body parts
nitrofurantoin for UTI
Erythromycin cant cross into CSF because it is too big and lipophilic
What does the CLSI seperate antibiotics into
4 groups
A- primary agents should be reported
B-secondary that are conditionally or selectively reported
C-supplemental antibiotics and that selectively reported
U - ABtic reported in urinary specimen
When are antibiotics in group B and C reported
-when org is resistant to antibiotics in Group A
-the pt cant tolerate the AB in group A
-the infection isnt responding to treatment
-when B or C are better for specific infections like meningitis
-when pt has an infection which B and C would cover in treatment
What strategies are used when prescribing AB - antimicrobial stewardship
- Dose optimization
- Antibiotic restrictions
- Physician education
- Cascade reporting
- Antibiogram studies
enzyme based antibiotics because there are lots of resistances
physicians, micro lab and pharm on the stewardship team
anti biogram to determine resistance of org based on cities, or hospitals
What is used for performing AST
MIC- vitek and KB
What is broth mAcrodilution testing
MIC - vitek
-Mueller hinton broth is made with known concentration of ABtic
-broth is diluted in half for next tube - doubling dilutions. This is repeated for all the subsequent tubes
-there will be a constant 0.5 mcF of bacteria in all tubes
-broth incubated overnight
-turbidity in the broths would indicated that the ABtic concentration was not enough to inhibit bacteria growth
-youll have a tube control and growth control
MIC is the lowest concentration of ABtic that prevents visible growth
-AST CARDS
how are MICs determined
-vitek uses light scatter
-based off clinical response data so what concentrations of AB where effective at treating the organism
-when you use known concentration that was given to the pt and its responsiveness you can determine what concentrations are sensitive and resistant
-breakpoints are values that can be sensitive depending on body site (ABtic permeability), drug administration (IV vs ORAL)
What is the new category CLSI developed
SDD - susceptible dose dependent
-accounts for different dose intervals that can be preformed during treatment
add a comment that you need a higher dose for the abtic to be effective
What is Minimum Bactericidal concentration
- like MIC but tests for bactericidal concentration instead of inhibitory concentration
-not done frequently in lab but good for pt who are immunocompromised with severe infection who need the test done
-done in conjunction with MIC tube tests. After the tubes are incubated check for turbidity, 0.01 ml from each clear tube is subculture onto agar to see if the org is still viable
-the lowest concentration that grows less than 5 colonies on the plate is the MBC end point
Kirby Bauer plate reminders
Alpha and Beta Streptococci on MHBA
* Others non-fastidious organisms on regular MHA
how are zones determined on the KB
-created as they correlated with MIC
-a scatterplot is made that plots an orgs MIC to an ABtic and its correlating zone size
low mic with large zone - sensitive
high mic with small zone - resistant
What happens if QC for an AB fails QC
-susceptibility results are held back until you determine why it failed
-if ABtic issue then PT sample need to be repeated with functional ABtics
-If there is an issue with QC testing and not PT sample (wrong QC org used) it needs to be proven
-compare results with expected CLSI values
-done weekly if the AB is used frequently and passed the 15-30 day QC
-control ATCC strain is used as QC
if new AB passes everyday 15-30 days then you can use it weekly
Why do you get TRM as your result in the VITEK AST Card
If the growth control is negative, this will
terminate testing of the antibiotic and is why
you sometimes get ‘TRM’ as your result.
