Unit 1 Flashcards
Validity
how accurate a test is
Reliability
how often the expected result shows
SOP
standard operating procedures
Reference organism
ATCC strains - behave like an actual specimen in both physical and chemical characteristics, utilized to confirm the validity and reliability of media, reagents and biochemical procedures
ATCC
American Type Culture Collection
Exempt media
Certain media will not require user testing, based on CLSI guidelines. Manufacturer certification provided
Non-exempt media
User-prepared. Keep records of sterility, testing with QC organisms of all new batches
Panic values
communicated immediately to an authorized clinician and documented. Have read back to you
Turnaround time
time to complete test from sample arrival to results reported
QC
Internal activities that ensure diagnostic test accuracy
QA
external activities that ensure diagnostic test accuracy
Patent outcomes
reduced length, cost of stay, TAT diagnosis, customer satisfaction
Benchmarking
compare your labs results to that of your peers
Qualitative AST
measured by the quality
Quantitative AST
measured by the quantity
MBC
Minimum bactericidal concentration
SBT
Serum Bactericidal Tests
Microdilution
technique used to measure antibiotic susceptibility in which the drug is diluted in a broth
Peak level
draw when the dosage is expected to be highest
Trough level
draw before patient’s next dose
Intrinsic resistance
results from the normal state of organism
Acquired resistance
altered physiology and structure changes in organism
Mode of Action
how an antimicrobial funtions
Synergy
activity greater than activity of single most active drug
Antagonism
activity less than activity of single most active drug
Drug of choice
antibiotic treatment that will normally work against organism class
McFarland Standard
reference to adjust the turbidity of bacterial suspensions so the number of bacteria will be within a given range to standardize testing
Zone of inhibition
area around antimicrobial which is lysed
Interpretative categories
Susceptible
Intermediate
Resistant
Supplemental tests
additional confirmatory tests
Beca lactamase
enzymes that destroy penicillins and/or caphalosporins and are produced by a variety of bacteria
Emperic therapy
beginning antibiotic treatment before confirmed test results
Bacteriostatic
inhibits but does not kill
Ex. Chloramphenicol, erythromycin, clindamycin, tetracycline
Bacteriocidal
kills the target organism
Ex. aminoglycosides, beta-lactams, vancomycin, quinolones
Susceptible
infection caused by the tested organism may be treated with a recommended dose of antimicrobial
Intermediate
isolate may be inhibited by attainable concentrations of certain drugs
Resistant
isolates are not inhibited by the concentration of antimicrobial achievable with a recommended dose
MIC - Minimal Inhibitory Concentration
quantitative monitoring drug dosage schedules in serum or when diffusion tests are equivocal or impractival
MBC testing
Minimal bactericidal concentration (continuation of MIC)
How to read and interpret disk diffusion zone sizes
measure lysed area in mm by ruler. Compare to CLSI standards of resistance
Reading dilutions to determine MIC value
After plate is incubated the tech checks growth with the control. If a dilution shows the bottom two wells but not the top two then the MIC value is the lowest number you DONT see growth in
significance of SBC
Modification of broth dilution method that measures the bactericidal activity from patients serum during therapy against the bacterial pathogen isolated from the patient
SBC sample
patient’s serum
When to perform AST testing
a. Isolate clinical significant?
b. chance of resistance
C. standard methods avaliable
Beta Lactam Spectrum
Both
Beta Lactam Mode of Action
inhibit cell wall synthesis
Beta Lactam Examples
Ampicillin
Piperacillin/Tazobactam
Cephazolin
Imipenem
Beta Lactam Bacterio_____
Bacteriocidal
Oxazolidinones spectrum
Gram +
Oxazolidinones Mode of Action
initiates protein synthesis
Oxazolidinones Examples
Linezolid
Oxazolidinones Bacterio_____
Bacteriostatic
Aminoglycosides Spectrum
Gram + and gram - not anaerobic
Aminoglycosides Mode of Action
inhibit protein synthesis
Aminoglycosides Examples
Gentamicin
Aminoglycosides
Bacterio_____
Bacteriocidal
Glycopeptides Spectrum
Gram + topical
Glycopeptides Mode of Action
inhibit bacteria cell wall synthesis
Glycopeptides Examples
Vancomycin
Glycopeptides Bacterio_____
Bacteriocidal
Macrolides Spectrum
Gram +
Macrolides Mode of Action
Protein synthesis
Macrolides Examples
Erythromycin
Macrolides
Bacterio_____
Bacteriostatic
Fluoroquinolones spectrum
Both
Fluoroquinolones Mode of Action
inhibit DNA synthesis by binding DNA gyrases
Fluoroquinolones Examples
Levofloxacin
Fluoroquinolones
Bacterio_____
Bacteriocidal
Azoles Spectrum
Fungi
Azoles Mode of Action
disrupts fungal cell membrane
Azoles Examples
Fluconazole
Azoles Bacterio_____
Bacterostatic
Supplemental AST testing - when
detect complicated resistance mechanisms not evident on routine AST testing
Supplemental AST testing predictor drugs
oxacillin disk screen for penicillin resistance in strep pneumoniae
Beta lactamase testing
Visual detection of beta lactamase hydrolysis - colormetric reaction
Enzyme will disrupt the beta lactam ring. Wont bind to PBP and inhibit cell wall synthesis
Beta lactamase method
Chromogenic cephalosporin and acidometric - included on Neisseria test strip. Not useful for Enterobacteriaceae or Pseudomonas
You have been asked to perform QC (quality control ) on a new kit of API20E strips. . Is this function preanalytic, analytic, or postanalytic
Analytic
You have been asked to perform QC (quality control ) on a new kit of API20E strips. Name 3 possible organisms that would be appropriate for QC.
Gram negative rods from Enterobacteriaciae group or 2 from Entero and 1 non-Entero
You have been asked to perform QC (quality control ) on a new kit of API20E strips. What criteria should determine the organisms to be used?
Organisms that represent positive and negative reactions for all 20 test wells.
You have been asked to perform QC (quality control ) on a new kit of API20E strips. How can you be certain of the biochemical characteristics of the organisms used?
Using specific ATCC organisms recommended by the manufacturer
You have been asked to perform QC (quality control ) on a new kit of API20E strips. What type of information should be documented in the QC record for this testing?
Lot number Expiration date Test results Tech performing test Date
You have been asked to perform QC (quality control ) on a new kit of API20E strips. If erroneous results are obtained, name 3 sources of error.
Tech error - inoculum too heavy/light
Mixed culture
Incubation time/temp
Problems with kit - manufacturer or transport
A patient has been diagnosed with a UTI. A culture is sent to the lab and K. pneumonia has been identified. Name 2 testing methods that can be utilized to determine the susceptibility of various antimicrobials.
Disk diffusion and MIC
A patient has been diagnosed with a UTI. A culture is sent to the lab and K. pneumonia has been identified. Name 2 bacteriocidal antimicrobials that may be effective.
Gentamycin
Ceftriaxone
Levofloxacin
A patient has been diagnosed with a UTI. A culture is sent to the lab and K. pneumonia has been identified.. Name 2 bacteriostatic antimicrobials that may be effective
Tetracycline
Trimethoprim
Tigecycline
A patient has been diagnosed with a UTI. A culture is sent to the lab and K. pneumonia has been identified. The lab did not test this organism for vancomycin, why?
Ineffective against gram neg organisms
A patient has been diagnosed with a UTI. A culture is sent to the lab and K. pneumonia has been identified. Should levoflaxacin be tested?
Yes. Generally it is effective but acquired resistance is always possible.
A patient has been diagnosed with a UTI. A culture is sent to the lab and K. pneumonia has been identified. Does this organism exhibit intrinsic resistance to any antimicrobials?
Yes. Ampicillin and other beta lactams
Conditions for disk diffusion testing of S. aureus must come from which document?
CLSI
What type of light source should be used to view a disk diffusion plate
Reflected light
Supplemental AST testing is often required. What is the necessity for aminoglycoside screens
Detection of high-level resistance (HLAR) aminoglycoside
What is the test method utilized when CRE type resistance is suspected?
Modified Hodge Test
Name 2 methods for measuring the turbidity of the inoculum
McFarland Standard
Spectrophotometer
Name 2 criteria for selection of antimicrobial agents to be tested
Site of infection
method
availability
known resistance patterns
Class/spectrum of activity for:
Ampicillin
Beta lactam, both
Class/spectrum of activity for:
Cefazolin
Beta lactam, both
Class/spectrum of activity for:
Clindamycin
Lincosamide, gram pos (rarely gram neg)
Class/spectrum of activity for:
Levofloxacin
quinolone, both
Class/spectrum of activity for:
Piperacillin
Beta lactam, both
Class/spectrum of activity for:
Ticarcillin/Clav acid
Beta lactam combo, both
Class/spectrum of activity for:
Trime/Sulfa
combo, both
What are the possible problems and what measures should be taking if the following are observed when performing QC? Several E. coli zones are too large
Check inoculum
medium depth
medium pH
What are the possible problems and what measures should be taking if the following are observed when performing QC? Small colonies within the zone of tetracycline with S. aureus
Mixed culture
reisolate
resistant mutants
What are the possible problems and what measures should be taking if the following are observed when performing QC? Gentamycin zone too small with P. aeruginosa
Ca and/or Mg level too high in medium
What is the relationship between MIC and zone size?
- Regression graph
2. MIC breakpoints plotted against zone sizes, regression line is drawn. DD breakpoints are where lines intersect.
An organism with an increased MIC value will be expected to have an increased or decrease zone size?
Decreased
Name the 3 weekly QC organisms used for KB method
E. coli - 25922
P. aerug - 27853
S. aureus - 25923
Describe the action of the amoxicillin or ticarcillin/clavulanic acid combo
2 beta lactams- lactam/lactamase inhibitor. Inhibitor renders B-lactamase incapable, beta lactam drug exerts its activity
An oxacillin disk is used to test S. pneumoniae for penicillin. Why?
Due to increased resistance observed with penicillin, OX is more sensitive and reliable indicator.
Define empiric antimicrobial therapy
therapy that is started before knowing organism or susc. profile