General Terms Flashcards by Erin groat

Quality Control

internal activities that ensure diagnostic test accuracy

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Quality Assurance

external activities that ensure positive patient outcomes

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Minimum Bacterial Concentration (MBC)

the minimum concentration of antimicrobial needed to yield a 99.9% reduction in viable colony forming units of a bacterial or fungal suspension.

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Serum Bactericidal Tests (SBT)

lowest dilution of a patients serum that kills a standard inoculum of an organism isolated from a patient; it is related to the antibacterial level achieved in a patients serum and the bactericidal activity of the drug being used.

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Peak Levels

an element of Serum Bactericidal Tests (SBT). Serum sample collected when the antimicrobial concentration is at the highest point.

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Trough Levels

an element of Serum Bactericidal Tests (SBT). Serum sample collected just before the patients next dose.

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Intrinsic Resistance

resistance which results from the normal genetic, structural, or physiological state of a microorganism.

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Aquired Resistance

resistance which results from altered cellular, physiology, and genetic changes in the organisms genetic makeup (unpredictable and may be associated with only somes strains of a particular group or species).

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Synergy

activity of drug combination substantially greater than activity of single most active drug alone.

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Antagonism

activity of drug combination is substantially less than the activity of the single most active drug alone.

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Drug of Choice

predictability of a bacterial isolate’s susceptibility to the antimicrobial agents most commonly used against them.

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Beta Lactamase

enzymes that destroy penicillin and /or cephalosporin and are produced by a wide variety of bacteria. Enzymes will destroy the beta-lactam ring and antimicrobial cannot bind to PBPs and inhibit cell wall synthesis.

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Minimal Inhibitory Concentration (MIC)

quantitative, good for monitoring drug dosage schedules in serum, and also when diffusion tests are equivocal or impractical.

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What are the two levels of control used in the microbiology lab?

An expected positive result and negative result for a given test.

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How often is AST performed?

Weekly to ensure the precision and accuracy of supplies and techs.

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Antibiotic

an antimicrobial agent which is obtained and purified from other microbial organisms (usually fungi). Few true antibiotics are used today.

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Mechanism for intrinsic resitance: Anaerobic bacteria vs. aminoglycosides

Lack of oxidative metabolism to drive uptake of aminoglycosides

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Mechanism for intrinsic resitance: Gram negative bacteria vs. vamcomycin

Lack of uptake resulting from inability of vancomycin to penetrate the outer membrane

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“Mechanism for intrinsic resitance: Klebsiella spp. Vs ampicillin (a ?-lactam) targets
“

Production of enzymes (?-lactamases) that destroy ampicillin before the drug can reach the penicillin-binding protein (PBP)

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If you mistakenly adjusted the organism inoculum suspension to be equal to a number 1 McFarland turbidity standard, would the results be falsely resistant, sensitive, or not altered?

Resistant

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What arethe criteria for selection of antimicrobials to be tested (AST)

“Site of infection
Method
Availability (formulary)
Knownn resistance patterns”

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What are the 3 weekly QC organisms used to the Kirby Bauer method?

“E. coli 25922
P. aeruginosa 27853
S. aureus 25923”

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Examples of preanalytical QA components

“Patient preperation
Sample collection
Sample storage, handeling, and transport
Information dissemination to medical staff”

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Examples of analytical QA components

“Preventive maintenance on equipment
Instrument function checks and calibrations
Quality control and management of media and reagents”

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Examples of postanalytical QA components

"Recording of results Priliminary reports with only information known at time (include procedures underway, and appropriate further testing) Final reports with no ambiguity Panic values communicated immediately Transmission of results within an acceptable interval"

Enterococci are resistant to which antimicrobials?

``` "Aminoglycosides (lack sufficient oxidative metabolism) Cephalosporin antibiotics (Lack of PBPs)" ```

Troubleshoot AST universally large zones

"Inoculum too light Nutritionally poor medium Media too thin Slow growing organism"

Troubleshoot AST universally small zones

"Inocculum too heavy | Agar depth too think"

Troubleshoot colonies within zone of inhibition

"Mixed Culture | Resitant mutants within zone (report as resistant)"

Criteria for AST testing

"Is the bacterial isolate clinically significant? Organism resistance (drug of choice) Standardized methods available"

AST quality factors

``` "Inoculum 0.5 McFarland Temp 35 degrees Atmosphere CO2 or ambient air Time 16-24 hrs Antimicrobial concentration Media thickness and pH (Mueller Hinton)" ```

Carbapanem resistant Enterobacteriaceae (CRE)

"Enterobacteriaceae with high levels of resitance to antibiotics Klebsiella and E.coli can become carbapenem resistant Plasmid borne resistant mechanism and are capable of crossing genetic elements from one organism to another"

Why should you not incubate the disk diffusion plate in a carbon dioxide (CO2)–enriched incubator?

It will alter the pH and affect the zone sizes.

While reading a disk diffusion susceptibility test, you notice a faint haze of growth to the edge of the sulfamethoxazole disk and a more pronounced zone that measures in the sensitive range. Is the drug S, I, or R?

Sensitive

Your Mueller-Hinton agar is 3.5 mm in depth (too thin). How will this affect the results? Will they be falsely sensitive or falsely resistant? Will the zones be too large or too small?

Sensitive. Too large

In recording the results of a microdilution tray, you notice that a slight haze is present in all the trimethoprim-sulfamethoxazole wells. Will you record the result as susceptible or resistant?

Susceptible

What could be the cause of small zones with p. aeriginosa (AST)?

Ca or Mg levels are too high in the media

What is the relationship between MIC and zone sizes?

As the MIC increases, zone size will decrease.

Describe the action of the (amoxicillin or ticarcillin)/clavulanic acid combination.

2 beta lactams beta lactam/ beta lactamase inhibitor. Inhibitor renders B-lactamase incapable , beta lactam drug (b-lact sens.) exerts it’s 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

What should be done if S. pneumoniae is resistant to oxacillin?

Perform MIC for conformation.

Empiric antimicrobial therapy

Therapy which is started before a positive organism ID.

Pseudomonas aeriginosa is resistant to which antimicrobials

Sulfonimides, trimethoprim, tetracycline, or chloramphenicol (Lack of uptake)

Klebsiella spp. Are resistant to which antimicrobial?

Ampicillin (production of Beta-lactamases)

Aerobic bacteria are resistant to which antimicrobials?

Metronidazole (inability to anaerobically reduce drug to it's active form)

Lactobacilli are resistant aginst which antimicrobials?

Vancomycin (cell wall structure)

Stenotrophomonas maltophilia are restsant against which antimicrobial?

Imipenem (drug cant reach PBPs)

McFarland turbidity standard

0.5=1.5x10^8 bacteria/mL

Which accredited agency tests AST

CAP

Chromogenic cephalosporin test

allows direct detection of beta-lactamas producion (pink is positive)

Which organisms are routinly tested for beta lactamase production?

H. influenzae, N. gonorrhea, Staph spp., Moraxella spp.

Extended Spectrum Beta-Lactamase (ESBL)

enzymes that meidate resistance to extended spectrum (third generation) cephalosporins and monobactams, but do not affect cephamycins or carbapenems

Which organisms should be tested for ESBL?

Enterobacteriaceae

ESBL positive rsults in what kind of zones of inhibition?

Enhanced

Describe a CRE positive

Lawn of E. coli with 3 applied organisms. CRE positive organisms will destroy Imipenem and allow E. coli to grow

What class of drugs is MRSA resistant too? Why?

Beta-lactams; organism produces altered PBPs and antimicrobial cannot inhibit cell wall synthesis.

What test is used to screen MRSA?

Oxacillin Salt agar test

Chromogenic agar is used to test for which organism?

MRSA; positive= blue colonies; agar is selective and differential

A vancomycin screen tests for

resistant Enterococcus (VRE) and resistant or intermediate Staphylococcus (VRSA, VISA)

An aminoglyceride screen tests for

high level aminoglycoside (HLAR), gentamycin or streptomycin resistance in Enterococcus

How would Strep pneumoniae be tested for penicillin resistance?

Oxacillin disk