Abstract
The urinary bladder in healthy dogs has dogmatically been considered free of bacteria. This study used culture independent techniques to characterize the healthy canine urinary microbiota. Urine samples collected by antepubic cystocentesis from dogs without urinary infection were used for DNA extraction. Genital tract and rectal samples were collected simultaneously from the same dogs. The V4 hypervariable region of the 16S rRNA bacterial gene was amplified and compared against Greengenes database for OTU assignment and relative abundance for urine, genital, and rectal samples. After excluding 4 dogs with cultivable bacteria, samples from 10 male (M; 1 intact) and 10 female (F) spayed dogs remained. All samples provided adequate genetic material for analysis. Four taxa (Pseudomonas sp., Acinetobacter sp., Sphingobium sp. and Bradyrhizobiaceae) dominated the urinary microbiota in all dogs of both sexes. These taxa were also detected in the genital swabs of both sexes, while the rectal microbiota differed substantially from the other sample sites. Principal component (PC) analysis of PC1 through PC3 showed overlap of urinary and genital microbiota and a clear separation of rectal swabs from the other sample sites along PC1, which explained 44.94% variation. Surprisingly, the urinary microbiota (mean # OTU 92.6 F, 90.2 M) was significantly richer than the genital (67.8 F, 66.6 M) or rectal microbiota (68.3 F, 71.2 M) (p < 0.0001), with no difference between sexes at any sample site. The canine urinary bladder is not a sterile environment and possesses its own unique and diverse microbiota compared to the rectal and genital microbiota. There was no difference between the sexes at any microbiota sample site (urine, genital, and rectal). The predominant bacterial genus for either sex in the urine and genital tracts was Pseudomonas sp.
Highlights
Over the past decade there has been increasing scientific evidence, in both humans and domestic species, supporting the important role of an individual’s microbiome on health and wellness
Due to bacterial growth on routine culture, 4 samples were excluded from further analysis, leaving 10 samples each from female and male (9 castrated, 1 intact) dogs
While this method continues to be the gold standard for the diagnosis of clinically relevant urinary tract infection (UTI) in dogs, it should be recognized that the treatment and resolution of UTI is likely a more complex process than elimination of bacteria identified using only routine anaerobic and aerobic urine cultures[1, 5, 22]
Summary
Over the past decade there has been increasing scientific evidence, in both humans and domestic species, supporting the important role of an individual’s microbiome on health and wellness. While the majority of studies in both human and veterinary medicine have focused on the gastrointestinal microbiome, rich, site-specific bacterial communities have been documented in other tissues previously considered to be sterile[1,2,3,4,5].With the advent of extremely sensitive culture-independent methods of characterizing complex microbial communities (e.g., metagenomics and 16S rRNA sequencing), evaluation of these microbial communities is increasingly feasible These methods allow for the identification of specific bacterial, archaeal, fungal, and viral strains, even in instances of minimal colonization[6]. This and other studies have shown that routine urine culture is insensitive for detection of most bacterial species found in the urogenital tract including uropathogens[1, 3, 19, 22]
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