A 3-year-old, female, spayed, domestic shorthair cat was presented to the primary veterinary clinic for malaise, anorexia, stranguria, periuria, pollakiuria and macroscopic haematuria. The cat had no previous pertinent medical history, and had been spayed at 5 months of age, with no abnormalities or complications noted during or after surgery. No abnormalities were noted on clinical examination, and the cat was prescribed an empirical 6 day course of amoxicillin/clavulanic acid tablets at 12.5mg/kg q12h (Clavulox; Zoetis Animal Health). This treatment did not result in improvement, prompting a revisit 1 week later. A cystocentesis sample revealed well-concentrated urine (specific gravity 1.050), with microscopic haematuria and trace protein noted on dipstick evaluation. No urine culture was performed. A soft, proliferative mass was seen protruding from the vulva; a grab biopsy sample of this tissue was collected under general anaesthesia. Pending histopathology the cat was prescribed prednisone orally at 5 mg q12h for 7 days, reducing it to 5 mg q24h for 7 further days and further amoxicillin/clavulanic acid at the previous dose. Dietary management included a specific veterinary diet (Urinary Care; Royal Canin). Histopathology at a reference laboratory (New Zealand Veterinary Pathology, Hamilton) revealed dysplastic squamous epithelium, with moderate numbers of neutrophils, macrophages and activated fibroblasts, resulting in a diagnosis of chronic granulomatous and proliferative vaginitis with marked epithelial dysplasia. Despite initial improvement with the new treatment regime, malaise, lethargy, vaginal swelling, macroscopic haematuria and periuria persisted, and so the cat was referred to an internal medicine specialist for further evaluation. On presentation to the Veterinary Specialist Group, the sole abnormality noted on physical examination was a small, fleshy, erythematous mass protruding from the vaginal vault. Feline immunodeficiency virus and feline leukaemia virus ELISAs were negative (SNAP FIV/FeLV combo; IDEXX Laboratories). Abdominal ultrasound (iE35, C8-5 probe; Philips) identified free-floating and slowly settling echogenic debris and a single, 2.7 mm diameter mineralised structure revealing gravity dependence within the urinary bladder. The urinary bladder wall thickness was within expected normal limits. Imaging from a perineal window identified a vaginal mass effect greater than 3 cm in size with mixed echogenicity, a hyperechoic centre and a hypoechoic periphery (). The caudal limits of the lesion had a bulbous shape while the cranial limits revealed a thickened fusiform shape. The bulbous shape was approximately 1.3 cm in diameter. Vaginoscopy, performed under general anaesthesia using a 3.5 mm rigid endoscope (64019 BA, 1030340 camera, DX PAL 202420-20 processor; Karl Storz) identified an extensive, fleshy, friable, irregularly shaped mass with diffuse attachment to the mucosa within the vaginal vault. Thick, firm, white exudate was present, particularly around the cranial aspect of this lesion. It was difficult to discern normal anatomy owing to the pathology present. Extensive debridement and biopsy of abnormal tissue was performed with 2.8 mm round-cup biopsy forceps (FB-35C-1; Olympus). The urethral orifice was not visible; however, a urinary catheter was passed blindly to ensure urination after mass debridement. Culture of the fresh tissue at a reference laboratory (Gribbles Veterinary, Auckland) produced a heavy growth of E coli, sensitive to amoxicillin/clavulanic acid, cephalothin, enrofloxacin, trimethoprim sulpha, polymyxin B and neomycin by standard disc diffusion testing. The cat was hospitalised with the urinary catheter in situ for 48 h, and then discharged with no complications noted. In the light of the culture, sensitivity and histopathology results, enrofloxacin (Baytril; Bayer Animal Health) was prescribed at a dose of 5 mg/kg q24h for 6 weeks. This resulted in rapid and complete resolution of the clinical signs and the cat is clinically normal 1 year after treatment. The biopsy samples were fixed in 10% neutral buffered formalin before routine histological processing and embedding in paraffin wax. On histopathological examination the biopsies were well preserved, and lined by dysplastic squamous epithelial cells; similar cells also formed cords, islands or glandular/ductular structures infiltrated by neutrophils within the samples (presumed dysplastic vestibular glands). The adjacent stroma was heavily and diffusely infiltrated by neutrophils, lymphocytes and plasma cells admixed with many macrophages (). These had abundant, faintly granular eosinophilic cytoplasm, with variably strong PAS-positive staining (). The macrophages sometimes contained a neutrophil, vacuolated space or short bacterial rods, found to be gram-negative on Gram staining (); similar rods were also seen apparently within neutrophils. These were not acid-fast with Ziehl–Neelsen stain. No basophilic bodies were seen within macrophages on haematoxylin and eosin or von Kossa stains. Unstained sections (5 μm on charged glass slides) of formalin-fixed, paraffin-embedded tissue were submitted to Cornell University for fluorescence in situ hybridisation (FISH) analysis with a eubacterial probe and an E coli probe as described previously. Specificity of hybridisation was controlled by co-hybridisation with an irrelevant labelled probe (non-EUB-338 [ACTC-CTACGGGAGGCAGC-6-FAM]), and the use of control slides of cultured E coli, Streptococcus species and Proteus species. Hybridised samples were washed in phosphate-buffered saline, allowed to air dry and mounted with a ProLong antifade kit (Molecular Probes). Sections were examined on an Axioskop 2 (Carl Zeiss) or a BX51 (Olympus America) epifluorescence microscope, and images were captured with a Zeiss Axiocam or Olympus DP-7 camera, respectively. Multifocal clusters of short- and medium-sized rods that hybridised with eubacterial probe 338 were visualised within cells that were consistent with macrophages within mucosa. These bacteria also hybridised with E coli/Shigella species probe, indicating the presence of intramucosal infection with E coli ().