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To investigate the antimicrobial properties of canine urinary extracellular vesicles (UEVs).
Free catch urine samples were collected from dogs presenting to the Queen’s Veterinary School Hospital. Samples with active sediments or dipstick abnormalities were excluded. UEVs were isolated from urine samples by differential ultracentrifugation and incubated with 60-153 colony forming units (cfu; 300-765 cfu/mL) of BL21 E.coli. UEVs were considered antimicrobial if the area under the growth curve of bacteria co-incubated with UEVs was significantly less than bacteria co-incubated with phosphate buffered saline. UEVs were quantified using nanoparticle tracking analysis and compared between groups using the Mann Whitney U test. Data are presented as median [range].
Canine urine contained 0.5 [0.04-13.2] billion UEVs/mL (n=15) and 68 [5-1500] million UEVs/μmol creatinine (n=12). UEV preparations from 14/23 dogs were bactericidal with antimicrobial preparations containing higher numbers of UEVs compared to non-antimicrobial preparations (28.6 billion [3.2 billion – 429 billion] UEVs/mL vs. 6.8 billion [1.2 billion – 123 billion] UEVs/mL; P=0.023), although there was significant overlap between groups. 13.2 billion UEVs/mL (corresponding to maximal excretion rate observed in dogs) were antimicrobial against 300-765 cfu/mL BL21 E.coli in 11/14 dogs.
Canine UEV preparations demonstrate antimicrobial activity at physiologically relevant concentrations, although the potency of UEV antimicrobial activity is variable between individuals. Further studies of UEV antimicrobial activity in dogs with recurrent urinary tract infections and subclinical bacteriuria are warranted.
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