Antimicrobial Susceptibility Flashcards
You are presented with a 2 year old quarter horse that has a large submandibular mass that feels warm and tender on palpation, what sample is the most ideal to submit for your patient?
(FNA)
What answer would you receive back when you complain that you did not get your susceptibility results back when Streptococcus spp. are identified in your sample?
(Beta hemolytic Streptococcus spp. have predictable susceptibility to first line antimicrobial therapies)
(T/F) Susceptibility testing is not needed when systemic antimicrobial therapy will not be used.
(T)
(T/F) Susceptibility testing is not needed when a probable pathogen has not been identified or your identified pathogen has a predictable susceptibility pattern.
(T)
(T/F) Susceptibility testing is not possible for all pathogens, for example Nocardia spp.
(T)
(T/F) Clostridium spp. are predictably susceptible to penicillin but can still be difficult to treat depending on the site of infection.
(T, especially if dealing with a necrotic site)
What do susceptible, intermediate, and resistant mean?
(Susceptible → growth inhibited by a concentration of an abx associated with a high likelihood of therapeutic success (NOT GUARANTEED); intermediate → growth inhibited by a concentration of an abx associated with an uncertain therapeutic effect (can change uncertainty by increasing dose or decreasing dose interval); resistant → growth inhibited by a concentration of an abx associated with a high likelihood of failure)
What is the 90-60 rule?
(In an immunocompetent patient with a monobacterial infx, bacteria reported as susceptible are associated with a positive therapeutic response in 90% of patients and bacteria reported as resistant are associated with a positive therapeutic response in 60% of patients)
(T/F) An anaerobic culture for a urine sample in a patient with signs of a UTI is a waste of money.
(T, do not need anaerobic culture for urine, anaerobic organisms unlikely to cause UTI)
What do you do if you started empirical treatment for a dog with a UTI and your susceptibility report comes back with that abx being an intermediate drug?
(Check on the dog; if getting better finish the course, if not getting better switch to susceptible drug)
How does reporting where you obtained your sample affect reported MIC values?
(Drugs achieve different concentrations in different parts of the body so that may change the MIC and if the drug will be reported as S, I, or R)
What is an antimicrobial breakpoint?
(The maximum MIC that predicts successful therapy, essentially tells you if an organism is S, I, or R by taking into account the normal range of MIC values in wild type bacteria, the PK/PD properties of the drugs in the species of interest, and +/- site of infection)
If everything on your susceptibility report comes back as susceptible, you should just pick the drug with the lowest MIC right?
(No, susceptible is susceptible, think more about cost and owner compliance and let that guide your choice if you have a long list of options)
(T/F) Many vets in practice will not ever use MIC values and they are typically only to be used when there is a patient with limited options for abx therapy.
(T)
(T/F) Topical antimicrobials have much higher concentrations than can be achieved through oral or parenteral dosing.
(T, this matters bc MIC breakpoints are based on systemic concentrations of antimicrobials, this is why if you are using topicals, susceptibility testing is unnecessary)
