Dr. Mark Papich- Antimicrobial Resistance and Antimicrobial Susceptibility Testing
Q: It was mentioned earlier that too long exposure to antibiotics may lead to increased resistance but can too short treatment also be an issue? How do you determine the ideal treatment time? Do the guidelines by the International Society for Companion Animal Infectious Diseases or similar guidelines detail this information?
A: That is an excellent question. Long exposure extends selection of resistance. The shortest course possible is the best approach. It is now known that short treatments for many infections (for example 5 days instead of 10 days) can be effective for some infections. A short course of treatment does not cause more resistance. This was discussed in a concise review paper published 2 years ago called “The antibiotic course has had its day. British Medical Journal. 2017 Jul 26; 358.”, by Llewelyn et al. The authors say “With little evidence that failing to complete a prescribed antibiotic course contributes to antibiotic resistance, it’s time for policy makers, educators, and doctors to drop this message.”
Q: For Enterococcus where the 2018-ed did not have vet-specific breakpoints, what do you use? The human breakpoints of 8? Or the vet-specific ones which are much lower?
A: Thank you for this question. We have guidelines for reporting Enterococcus susceptibility. These are provided in our Vet01 document. Essentially, we rely on testing for aminopenicillins first, and if the strain is susceptible to aminopenicillins, they can be considered a susceptible strain. CLSI also has recommendations for testing high-level resistance with gentamicin. These recommendations are adapted from the human documents. Enterococcus strains with ampicillin and penicillin MICs greater than 16 mcg/mL are categorized as resistant. However, enterococci with low levels of penicillin or ampicillin resistance may be susceptible to synergistic killing by these penicillins in combination with gentamicin.
Often in companion animals we identify Enterococcus from a culture, but do not consider it an important pathogen and we may withhold antibiotics unless there are obvious clinical signs associated with the isolate.
Q: I am in the academia and a veterinarian in a medical university, I am interested to know how antibiotic use has affected emergence of opportunistic fungi?
A: We do not have any studies that this occurs, although it is highly likely in some situations. The most common example that is available (anecdotal from dermatologists) is antibiotic administration to dogs to treat a skin infection. After the commensal skin bacteria are suppressed, sometimes the dog develops a yeast infection caused by Malassezia. This may occur in other situations, but has not been studied sufficiently.
Q: It has been noticed on one of the slides of your presentation that the doxycycline breakpoint has been revised from 8ug/ml to 0.125ug/ml. In practice, if the revised lower dose shows no clinical improvement, should one increase to the previous dosage?
A: Thank you for this question. The new equine breakpoint for doxycycline is very low. The reason for this low breakpoint is that doxycycline has low oral absorption in horses and the plasma drug concentrations are so low that a breakpoint of 8 mcg/mL (human breakpoint) is way too high. Our analysis showed that 0.125 mcg/mL will be appropriate to reach therapeutic PK-PD targets. If a patient does not respond, there is a risk in horses to raising the dose. At high doses of doxycycline, more of the drug remains in the intestine and colic and enteritis are highly likely. At this breakpoint, the only bacteria that are susceptible are the Streptococci and some Staphylococcus.
Dr. Stefan Hobi- Antimicrobial Resistance in Canine Pyoderma and Treatment Options
Q: Are the majority of pyoderma cases in dogs caused by Staphylococcus aureus?
A: The majority of pyoderma cases in dogs are caused by Staphylococcus pseudintermedius but Staphylococcus aureus can be a problem too.
Q: I have isolated Staphylococcus aureus from pyoderma cases which responded to amoxicillin/clavulanic acid. Some practitioners use antibiotics since it serves as security blanket against possible infections.
A: I also have some pyoderma cases caused by Staphylococcus aureus. Some of them are very sensitive and some of them are super resistant; so it is absolutely possible that it responds to amoxicillin/ clavulanic acid.
Q: Do Immunoglobulins serve as form of passive immunity in the treatment of pyoderma?
A: In humans, sometimes IgG immunoglobulins are used intravenously as part of the treatment of pyoderma. We do not know the mechanism exactly yet. The possible mechanisms include immunomodulatory effects, neutralisation of the toxins or making neutrophils and macrophages more efficient.
Q: Is Malassezia zoonotic?
A: This is a very good question! Malassezia can be shared between animals and humans but we do not have a lot of information about this yet. Hopefully more information will be available in the near future.
Q: What antimicrobials are prescribed best for deep pyodermas? Do you recommend clindamycin because of anaerobes?
A: For deep pyodermas, I would really advise taking a sterile sample and treating according to the culture results
Dr. Derek Chow- Antimicrobial Therapy in Veterinary Ophthalmology
Q: Are you suggesting not giving ointment type antibiotics for corneal ulcer?
A: Not when there is a perforation at the cornea.