Transmission of Escherichia coli Causing Pyometra between Two Female Dogs

Abstract

Despite its clinical relevance, the pathogenesis of canine pyometra remains poorly understood. To date, it is recognized as a non-transmissible infectious disease. In this study, the simultaneous occurrence of pyometra and Escherichia coli in two cohabitant female dogs underwent in-depth investigation due to the hypothesis of transmission between these animals. Two 5-year-old Chow Chow dogs (namely, dogs 23 and 24-D23 and D24) were referred to a veterinary hospital with suspected pyometra. Both animals showed prostration, anorexia, and purulent vulvar discharge over a 1-week period. After ovariohysterectomy, uterine tissue, uterine contents, and rectal swabs were collected for histopathological and microbiological analysis. Uterine histology demonstrated purulent material and multifocal necrosis with endometrial ulceration, and a morphological diagnosis of pyometra was confirmed. Furthermore, E. coli from the same phylogroup (B2) and positive for the same virulence factors with the same antimicrobial susceptibility profile was isolated from the uterine contents of both dogs and the rectum of D23. Conversely, the E. coli strains recovered from D24 differed in phylogroup (one isolate), virulence factors (all three isolates), and antimicrobial susceptibility (all three isolates). Enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) suggested that all isolates from the uterine content of both dogs and the rectal swab of D23 were 100% the same, but different from all isolates in the rectal swab of D24. One isolate from the uterine content of each animal as well as rectal swabs were subjected to whole-genome sequencing (WGS). Both whole-genome multilocus sequence typing(wgMLST) and single-nucleotide polymorphism (SNP) analysis supported the hypothesis that the isolates from the uterine content of both animals and the rectal swab of D23 were clonal. Taken together, these clinical features, pathology, microbiology, and molecular findings suggest, to the best of our knowledge, the first transmission of E. coli associated with pyometra between two animals. These results could impact the management of sites where several females cohabit in the same local area such as kennels.

Keywords: EnPEC; ExPEC; UPEC.

Figure 1

Canine uteri. (A) D23—uterine lumen filled with large amounts of blood and increased cellularity in the endometrium, with severe necrosis, endometrial ulceration, and hemorrhage. Endometrial glands are markedly ecstatic. (B) D23—higher magnification of A: hemorrhagic uterine luminal content, with neutrophils, plasma cells, fibrin, and bacterial aggregates (arrow). (C) D24—severe diffuse endometritis, with endometrial glands markedly ecstatic with an accumulation of inflammatory cells and mucous, and superficial luminal and glandular epithelium composed of columnar and finely vacuolated cells. (D) D24—higher magnification of C: severe diffuse interstitial lympho-histioplasmacytic infiltrate, and an endometrial gland filled with neutrophils. Hematoxylin and eosin, scale bars = 500 µm (A,C), 60 µm (B,D).

Figure 2

Enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) similarity, virulence factors, phylogroup, and antimicrobial profile of E. coli isolated from rectal swabs and uterine contents of two cohabiting bitches (D23 and D24). Legend: P: uterine content; S: rectal swab, AMC: amoxicillin/clavulanic acid, AMP, ampicillin, CTF: ceftiofur, CIP: ciprofloxacin, ENO: enrofloxacin, NEO: neomycin, GEN: gentamicin, DOX: doxycycline, OT: oxytetracycline, and SUT: trimethoprim/sulfamethoxazole. Isolates marked in red were selected for whole genome sequencing.

Figure 3

goeBURST population snapshot of clonal complex (CC) 372. Only isolates with a single locus variance (SLV) and isolates from the present study were included: the S24 isolate is marked in blue; ST372 (founder) is marked in orange, P23 is marked in red, and other isolates obtained from the public E. coli MLST database are marked in gray; line numbers indicate allelic variance.

Figure 4

wgMLST phylogeny tree including the present study isolates (in red) and reference strains added for comparison purposes.