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Prevalence of positive reactions in intradermal and IgE serological allergy tests in dogs from South Australia, and the subsequent outcome of allergen-specific immunotherapy

Han C, Chan WY, Hill PB

Aust. Vet. J., 2020 Jan;98(1-2):17-25.
PMID: 31742667 DOI: 10.1111/avj.12892

OBJECTIVE: To determine the prevalence of positive allergen reactions in intradermal and IgE serological tests in dogs presenting to a dermatology referral centre in South Australia and the clinical efficacy of subsequent allergen-specific immunotherapy.
DESIGN: Retrospective study.
METHODS: Results from 108 intradermal allergy tests, 25 IgE serological assays and immunotherapy outcomes in 37 dogs were retrospectively analysed. Immunotherapy outcomes were determined as excellent, good, modest or failure using a global assessment of efficacy matrix which incorporated pruritus scores, lesion severity, medication requirements, and owner and clinician opinion.
RESULTS: The most common positive reactions in intradermal allergy tests were Red clover (59%), Dermatophagoides farinae (29%), Tyrophagus putrescentiae (28%), Yellow dock (25%) and Malassezia pachydermatis (24%). In the IgE serological tests, Yorkshire fog grass (40%), Yellow dock (36%), Kentucky bluegrass (36%) and T. putrescentiae (36%) were the most commonly reported positive results. The outcome of allergen-specific immunotherapy was judged to be excellent in 20% of dogs, good in 15%, modest in 18% and a failure in 47%.
CONCLUSION: As has been reported in other geographical areas, environmental mites and plant pollens frequently gave positive reactions in allergy tests in South Australia. However, the prevalence of individual allergen reactions differed between intradermal and IgE serological tests, with M. pachydermatis being identified as a common cause of hypersensitivity in intradermal tests but not in IgE serological assays. Immunotherapy was judged to be a beneficial treatment in 35% of dogs but was essentially unsuccessful in 65%.
In vitro antimicrobial activity of narasin and monensin in combination with adjuvants against pathogens associated with canine otitis externa

Chan WY, Hickey EE, Khazandi M, Page SW, Trott DJ, Hill PB

Vet Dermatol, 2020 Apr;31(2):138-145.
PMID: 31710159 DOI: 10.1111/vde.12803

BACKGROUND: The emergence of antimicrobial resistance represents a serious human and animal health risk. Good antimicrobial stewardship is essential to prolong the lifespan of existing antibiotics, and new strategies are required to combat infections in man and animals.
HYPOTHESIS/OBJECTIVES: To determine the in vitro interaction of ionophores (narasin or monensin) with antimicrobial adjuvants (N-acetylcysteine (NAC), Tris-EDTA or disodium EDTA) against bacterial strains representing pathogens associated with canine otitis externa (OE).
ANIMAL/ISOLATES: American Type Culture Collection (ATCC) strains Staphylococcus aureus 29213, Pseudomonas aeruginosa 27853 and P. aeruginosa biofilm producer PAO1, and a clinical isolate of Proteus mirabilis from a case of canine OE were tested.
METHODS AND MATERIALS: A 2D microdilution checkerboard method was used, allowing calculation of fractional inhibitory concentration index (FICI), dose reduction index (DRI) and plotting of isobolograms.
RESULTS: The combination of narasin with either Tris-EDTA or disodium EDTA produced additive effects (FICI = 0.75) against P. aeruginosa ATCC 27853 and P. aeruginosa biofilm producer ATCC PAO1. An additive effect (FICI = 0.53-0.75) was found against S. aureus ATCC 29213 when narasin or monensin were combined with NAC. The highest DRI (32-fold) was found with monensin/NAC where the MIC of monensin was reduced from 4 to 0.125 μg/mL.
CONCLUSIONS AND CLINICAL IMPORTANCE: The combination of narasin with Tris-EDTA or disodium EDTA is a promising strategy to inhibit the intrinsic resistance elements of Gram-negative bacteria. These novel combinations potentially could be useful as a multimodal approach to treat mixed infections in canine OE.
Biofilm production by pathogens associated with canine otitis externa, and the antibiofilm activity of ionophores and antimicrobial adjuvants

Chan WY, Hickey EE, Page SW, Trott DJ, Hill PB

J Vet Pharmacol Ther, 2019 Nov;42(6):682-692.
PMID: 31503362 DOI: 10.1111/jvp.12811

Otitis externa (OE) is a frequently reported disorder in dogs associated with secondary infections by Staphylococcus, Pseudomonas and yeast pathogens. The presence of biofilms may play an important role in the resistance of otic pathogens to antimicrobial agents. Biofilm production of twenty Staphylococcus pseudintermedius and twenty Pseudomonas aeruginosa canine otic isolates was determined quantitatively using a microtiter plate assay, and each isolate was classified as a strong, moderate, weak or nonbiofilm producer. Minimum biofilm eradication concentration (MBEC) of two ionophores (narasin and monensin) and three adjuvants (N-acetylcysteine (NAC), Tris-EDTA and disodium EDTA) were investigated spectrophotometrically (OD570nm ) and quantitatively (CFU/ml) against selected Staphylococcus and Pseudomonas biofilm cultures. Concurrently, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of planktonic cultures were assessed. 16/20 of the S. pseudintermedius clinical isolates were weak biofilm producers. 19/20 P. aeruginosa clinical isolates produced biofilms and were distributed almost equally as weak, moderate and strong biofilm producers. While significant antibiofilm activity was observed, no MBEC was achieved with narasin or monensin. The MBEC for NAC ranged from 5,000-10,000 µg/ml and from 20,000-80,000 µg/ml against S. pseudintermedius and P. aeruginosa, respectively. Tris-EDTA eradicated P. aeruginosa biofilms at concentrations ranging from 6,000/1,900 to 12,000/3,800 µg/ml. The MBEC was up to 16-fold and eightfold higher than the MIC/MBC of NAC and Tris-EDTA, respectively. Disodium EDTA reduced biofilm growth of both strains at concentrations of 470 µg/ml and higher. It can be concluded that biofilm production is common in pathogens associated with canine OE. NAC and Tris-EDTA are effective antibiofilm agents in vitro that could be considered for the treatment of biofilm-associated OE in dogs.

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