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Veterinary Diagnostics > Antibiotic Susceptibility Testing > Flashcards

Antibiotic Susceptibility Testing Flashcards

1
Q

What does AST stand for?

A

Antimicrobial Susceptibility Testing

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2
Q

What does AST do?

A

Determines activity of antimicrobial against bacteria

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3
Q

What can you use AST on?

A

Bacteria, virus, parasite and fungi

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4
Q

What are some reasons an antibiotic may not be on your panel?

A

-Not approved for vet med
-Not approved for species
-Not useful for infection in that location
-Not effective against that bacteria (intrinsic resistance)

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5
Q

What are the methods of AST?

A

Phenotypic, Molecular and Mass Spectrometry

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6
Q

What is key to remember about breakpoints?

A

They change based on new studies and information

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7
Q

Describe the phenotypic method of dilution/automated?

A

-Make a broth dilution of the bacteria
-Add bacteria to plate with different concentration antimicrobials (may be preassem-bled)
-Incubate 18-24 hours
-Read growth
-Lowest concentration that inhibits bacterial growth is minimum inhibitory concentration (MIC)

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8
Q

Describe the phenotypic method of diffusion/gradient method?

A

-bacteria are made into standardized concentration into liquid and added to agar plate
-E-test strip of kirby bauer disc added
-incubate 18-24 hours
-No growth on plate (clear area) - zone of inhibition (MM)
-Read where bacteria growth meets the strip

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9
Q

What is a bacteriostatic drug?

A

-Inhibit bacterial growth and reproduction
-Inhibit RNA synthesis
-Delay bacteria until host immunity can kill

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10
Q

What is a bactericidal drug?

A

-Directly kill bacteria
-inhibit cell wall or DNA synthesis
-Not dependent on host response (rapid)

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11
Q

What is MIC?

A

Minimum Inhibitory Concentration
-lowest concentration of antimicrobial that inhibits growth and does not kill microbes

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12
Q

What is MBC?

A

-Minimum bactericidal concentration
-Lowest concentration needed to kill the microbe
-Bacteriostatic MBC to MIC >4
-Bactericidal MBC to MIC <4

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13
Q

What is a breakpoint?

A

Maximum MIC that predicts successful therapy

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14
Q

Who makes the MIC?

A

CLSI

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15
Q

What is considered when creating break points?

A

-Normal range of MIC in particular bacteria species
-PK/PD of drug in species of interest
-Site of infection
-Pharmaceutical company data
-Challenging cause cost money to get data to back these things up

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16
Q

What do ideal breakpoints combine?

A

Species, Drug, Bacterial Species and Site

17
Q

What do breakpoints tell you?

A

If the organism is suspectable (S), Intermediate (I) or Resistant (R)

18
Q

What does it mean if the organism is susceptible?

A

Concentration associated with high likelihood of therapeutic success

19
Q

What does intermediate mean?

A

Concentration associated with uncertain therapeutic effect
-efficacy in certain body sites
-buffer zone to prevent error
-Consider site of action, if local it may be ok

20
Q

What does it mean if it is resistant?

A

Should not use that drug
-concentration associate with high likelihood of therapeutic failure

21
Q

What do we do if there is no breakpoint?

A

Depends on the lab.
-Some will not report on that drug
-Some will use breakpoints from another species of animal or similar organism
-Some default to human breakpoints
-Some substitute similar organism in same genus
-NI or NN (inconclusive)

22
Q

When do breakpoints change?

A

When there is new data or when they are checked every 2 years

23
Q

So what if you plan to apply the antimicrobial topically? Can you trust the breakpoint?

A

No, breakpoints are based on systemic concentrations

-Much higher concentrations than through oral
-Can be R in systemic but work locally

24
Q

If there is a lack of response to your treatment dose that mean there is resistance? If it is not resistant then what could it mean?

A

No
-Poor penetration at that site
-Underlying disease or immunocompromised
-BIOFILM

25
Q

How do you know if a organism is resistant then?

A

-Phenotypic - AST and standard breakpoints
-Genotypic - gene ID, mecA staph, ESBL enterobacterales
-Intrinsic - target not available in that species
-Multidrug resistant - MDR- resistant to >3 antimicrobial classes

26
Q

When should I perform AST?

A

-Sample appropriately collected
-Appropriately transported to lab
-Evidence Inflammation
-Signiant growth isolated
-Want to use systemic antibiotics

27
Q

You have a case where you predict that strep equi is the causative agent. Do you need susceptibility? will you get results back?

A

No, and you would not because they are very predictable in susceptibility

28
Q

When is susceptibility testing not needed?

A

-Predictable susceptibility of pathogen
-No pathogen has been isolated
-If you suspect a fastidious organism
-when topical is indicated

29
Q

What are some bacteria with predictable suceptibilities?

A

Beta hemolytic streptococcus, clostridium, erytsipelothrix rhusiopathiae, listeria monocytogenes, bacillus anthracis, actinomyces, actinobacillus, haemonphilus, pasturella (except bovine), fusobacterium

May still be hard to treat

30
Q

A dog is having increased accidents, a UA is analyzed (Increase rbc, wbc and protien and gram + cocci), owner want culture and sensitivity, what kind of test do you order?

A

Aerobic culture and susceptibility (Anaerobes rare for a UTI)
-Start on enrofloxacin while waiting

31
Q

If the empiric antibiotic you are treating with comes back with an I on sensitivity what do you do?

A

-If patient is doing well don’t need to change but may want to increase dose if possible
-If not doing well switch to an S antibiotic (Or old and has other issues)

32
Q

You have a cocker spaniel with recurrent otitis enter the clinic. You send it off for culture and find staph pseudointermidius. Do you need sensitivity?

A

Yes!
MDR?

33
Q

What are some MRSP treatment options?

A

-Skin and ear infection common
-No rifampin by itself or become resistant way fast
-Topical therapy
-Mupirocin - last resort (top dog)
-Human meds (rare)

33
Q

If a patient returns like 3 months after treatment for the same thing do you need to culture and sensitivity it again?

A

Yes, things may have changed

34
Q

Can 2 organisms be causing and infection? How do you know which sensitivity to use?

A

Yes
Combine them and pick a drug that is S to both

35
Q

Are there any antibiotics to help with BIOFILMS currently?

A

No, doesnt take into account bacterial lifestyle

Can use Tris-EDTA, NAC, H2O2 and DMSO to try to break it up

Veterinary Diagnostics (13 decks)

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