Bacterial urinary tract infections (UTIs) often occur in association with canine urolithiasis. In this study, urine samples of 21 dogs with urolithiasis were collected by cystocentesis. Bacterial isolations were performed on this urine as well as on urinary bladder mucosal biopsy specimens and uroliths collected during cystotomy. Uroliths were analyzed for chemical composition. Bacterial UTI was discovered in 16 cases (76.2%).

Bacteria isolated included Escherichia coli (n = 7), coagulase-positive Staphylococcus species (n = 4), Klebsiella pneumoniae (n = 2), Pseudomonas aeruginosa (n = 2), and Proteus mirabilis (n = 1). In 11 cases (52.4%), bacteria were isolated from the urine and the same bacteria were also isolated from the bladder mucosa alone (42.9%) or from both the bladder mucosa and uroliths (9.5%). Ten cases (47.6%) yielded negative urine cultures; however, in 5 of these cases (23.8%), bacteria were isolated from either the bladder mucosa or the urolith. Uroliths from which bacteria were isolated were 1) infection-induced uroliths consisting of struvite and calcium carbonate phosphate or ammonium acid urate only or 2) metabolic uroliths composed of calcium oxalate plus calcium phosphate or calcium phosphate only. The uroliths that yielded negative bacterial cultures were all metabolic uroliths composed of calcium oxalate with or without calcium phosphate, or uric acid and calcium phosphate. Thus, the authors suggest that if a urine culture is positive before surgery, then culture of a bladder mucosal biopsy specimen or of the urolith is unnecessary. However, if a urine culture is negative, cultures of bladder mucosal biopsy specimens and uroliths should be performed to rule out underlying UTI because an additional 25% of UTI cases may be found.

COMMENTARY: This study emphasizes the need to follow up a negative urine culture with further diagnostics in dogs with urolithiasis to rule out UTI. This is of particular importance when owners choose to attempt medical dissolution or when surgery for urolith removal is declined. In these instances, a urine culture may be the only diagnostic test for UTI that is performed. Should the result of a urine culture subsequently come back negative and the owner declines bladder mucosal biopsy or culture of the urolith, it appears reasonable to advise the client that there is a 25% chance that the dog may still have an underlying UTI.

Comparison of three techniques for the diagnosis of urinary tract infections in dogs with urolithiasis. Gatoria IS, Saini NS, Rai TS, Dwivedi PN. J SMALL ANIM PRACT 47:727-732, 2006.