Urine culture as a test for cure: why, when, and how?

Quantitative urine culture before initiation of antimicrobial therapy is considered to be the gold standard for diagnosis of bacterial urinary tract infections (UTIs). In addition to facilitating differentiation of harmless bacterial contaminants from bacterial pathogens,accurate identification of specific bacterial species aids in selection of antimicrobial drugs. It also facilitates differentiation of recurrent UTIs caused by relapses from recurrent UTIs caused by reinfections.Failure to perform bacterial urine cultures or failure to interpret results of urine cultures correctly may lead not only to diagnostic errors but to therapeutic failures as well.     

Response of feline eosinophilic plaques and lip ulcers to amoxicillin trihydrate-clavulanate potassium therapy: a randomized, double-blind placebo-controlled prospective study

In this study, we evaluated the treatment of feline eosinophilic plaques and lip ulcers with amoxicillin trihydrate–potassium clavulanate (Clavamox^®; Pfizer Animal Health). Nineteen cats with clinical and cytological findings consistent with eosinophilic plaques and/or lip ulcers were enrolled. Lesions were photographed and their areas measured in square centimetres before and after 21 days of therapy with either flavoured amoxicillin‐clavulanate suspension or flavoured placebo suspension. Sixteen cats completed the study, with nine plaque lesions (four treatment and five placebo) and eight lip ulcer lesions (four treatment and four placebo) included in the analysis. All lesions were shown to have infection, with bacterial phagocytosis present on cytological examination. Coagulase‐positive staphylococci were the most commonly isolated bacteria. The amoxicillin‐clavulanate‐treated eosinophilic plaque group had a statistically significant 96.2% reduction in mean lesion size (?7.60 cm², P = 0.0078) and an 80% reduction in mean percentage of microscopic fields demonstrating evidence of bacterial infection (P < 0.0001), whereas the placebo group did not. The amoxicillin‐clavulanate‐treated lip ulcer group had a 42.6% decrease in mean lesion size (?0.25 cm², P = 0.4125) and the placebo group a 36.6% increase (+0.49 cm², P = 0.1575), although neither change was statistically significant. The amoxicillin‐clavulanate‐treated lip ulcer group had a statistically significant 65.0% reduction in mean percentage of microscopic fields demonstrating evidence of bacterial infection (P < 0.0001), while no significant reduction was observed in the placebo group. A suspension of amoxicillin trihydrate–potassium clavulanate is an effective monotherapy for the treatment of feline eosinophilic plaques.     

Comparison of wet-mount,Wright-Giemsa and Gram-stained urine sediment for predicting bacteriuria in dogs and cats

This study assessed the standard urinalysis technique and sediment stain techniques as predictors of bacterial culture results for canine and feline urine. Canine (n = 111) and feline (n = 79) urine samples were evaluated using unstained wet-mount and air-dried Gram and Wright-Giemsa stained sediment; results were compared to aerobic bacterial culture. Eleven canine and 7 feline urine samples were culture positive. Unstained wet-mount and stained sediment had sensitivities of 89% and 83% and specificities of 91% and 99%, respectively. The specificity of using either stain was higher (P < 0.01) than wet-mount examination for detecting bacteriuria. There were significant differences among 3 technologists in detecting true positives (P < 0.01). Association of sediment and culture results used 112 canine and 81 feline samples. There was a negative association (P < 0.01) between lipid detection and wet-mount identification of bacteria.     

Diagnosis of urinary tract infections.

Urinary tract infections (UTIs) are a common cause of urinary tract disease and may be associated with systemic disease. Diagnosis cannot be made on urinalysis and other findings alone. A urine culture is the "gold standard" for diagnosis of UTI. Antimicrobial susceptibility testing performed as part of a urine culture aids in selection of appropriate treatment for patients with confirmed bacterial UTI.     

Diagnostic utility and cost‐effectiveness of reflex bacterial culture for the detection of urinary tract infection in dogs with low urine specific gravity

Background: Urinary tract infections (UTIs) may be subclinical or difficult to detect in dilute urine as sediment abnormalities may not be observed. In our laboratory, bacterial culture is automatically performed (reflex culture) on samples with urine specific gravity (USG)≤1.013 to increase the likelihood of detecting infection. The value of routine culture of dilute urine, however, has not been fully assessed. Objective: The purpose of this retrospective study was to evaluate the frequency of positive bacterial cultures and analyze the diagnostic utility and cost‐effectiveness of culture compared with routine sediment examination for detecting UTI in dilute urine specimens from dogs. Methods: Urinalysis and concurrent aerobic bacterial culture results were obtained from the electronic medical record system at the University of California–Davis Veterinary Medical Teaching Hospital for samples with USG≤1.013 analyzed from July 1998 through January 2005. Urine collection method, presence of leukocytes and bacteria, bacterial culture results, and clinical diagnosis were recorded. Cost‐effectiveness of reflex culture, based on low USG as the sole criterion, was evaluated. Results: Of 1264 urine specimens, 106 (8.4%) had positive bacterial cultures. Using culture as the gold standard, sediment evaluation had a diagnostic sensitivity of 58.5% and specificity of 98.3% (diagnostic accuracy 94.9%). An additional cost of $60 per patient was incurred, leading to average annual costs of $11,668 for reflex bacterial cultures of all samples with low USG, regardless of collection method. Within our study population, 10 urine samples needed to be cultured for each true positive result. Conclusions: The sensitivity of urine sediment evaluation is low for UTI in dilute urine samples; however, reflex bacterial culture does not appear to be cost‐effective in dogs with USG≤1.013 in the absence of active urine sediment or high clinical suspicion for UTI.     

Cystocentesis is essential for reliable diagnosis of urinary tract infections in cats

Urine samples were taken from 79 cats with clinical signs of acute feline lower urinary tract disease (FLUTD) by means of cystocenthesis, catheterization, or at voiding and were cultured. No bacteria were cultured from 79% of the samples taken by cystocenthesis, 55% of the samples obtained by catheterization, and 17% of the samples obtained at voiding. Samples obtained by cystocenthesis most often yielded pure cultures, whereas the voided samples were often contaminated, yielding mixed cultures. Therefore, it is difficult to interpret culture results for voided or catheterized urine samples, which may lead to overdiagnosis of urinary tract infections. E. coli was the most prevalent bacterial species. Numbers of bacteria were low (10(2) to 10(3)/ml) in three out of eight culture-positive samples taken by cystocenthesis, indicating that the number of bacteria present in the bladder of cats with urinary tract infections may be low. This may lead to underdiagnosis of urinary tract infections when interpreting culture results for voided and catheterized samples, because bacterial counts lower than 10(3) colony-forming units/ml of urine are generally considered not clinically relevant. In conclusion, cystocenthesis is the preferred method of sampling for the evaluation of cats with suspected urinary tract infection.     

Medical dissolution of feline struvite urocystoliths

The efficacy of a diet designed to facilitate dissolution of feline magnesium ammonium phosphate (struvite) uroliths was evaluated in 30 cases of urolithiasis, sterile struvite uroliths dissolved in a mean of 36 days after initiation of dietary treatment. In 5 cases of urolithiasis, struvite urocystoliths associated with urease-negative bacterial urinary tract infection dissolved in a mean of 23 days after initiation of dietary and antimicrobial treatment. In 3 cases of urolithiasis, struvite urocystoliths associated with urease-positive staphylococcal urinary tract infection dissolved in a mean of 79 days after initiation of dietary and antimicrobial treatment. Dissolution of uroliths in cats fed the treatment diet was associated with concomitant remission of dysuria, hematuria, and pyuria, and reduction in urine pH and struvite crystalluria. In one case, a urocystolith composed of 100% ammonium urate, and in another case, a urolith composed of 60% calcium phosphate, 20% calcium oxalate, and 20% magnesium ammonium phosphate did not dissolve.     

Persistent urinary tract infections and reinfections in 100 dogs (1989-1999)

A retrospective study was performed of 100 dogs with persistent urinary tract infections (UTIs) or reinfections presenting to the North Carolina State University (Raleigh, NC) Veterinary Teaching Hospital between 1989 and 1999. Criteria for selection included > or = 2 positive urine cultures within a 6-month period. Signalment, presence of predisposing disorders, urinalysis and urine culture results, and treatment strategies were extracted from the medical records. Dogs were a median age of 7 years when the UTI was 1st diagnosed. Dogs younger than 3 and older than 10 years were at increased and decreased risks, respectively, for reinfections or persistent UTIs. Spayed females were more common in the UTI population. More than half of the dogs were asymptomatic for a UTI at 1st presentation. Urine sediment examinations identified hematuria, pyuria, and bacteriuria in 47, 72, and 85% of the samples, respectively. The most commonly isolated organisms were Escherichia coli and Streptococcus/Enterococcus spp.; multiple isolates also were common. Of the isolates, 29.5% were resistant to achievable serum concentrations of all antibiotics commonly prescribed for PO administration. Dogs with abnormal micturition were more likely to have infections by organisms resistant to commonly prescribed antibiotics. Potentially predisposing disorders were identified in 71 dogs. A correction of these disorders was accomplished in 35% of these 71 dogs. Dogs given standard antibiotic therapy without addressing predisposing disorders experienced poor control of their UTIs; 74.5% of these dogs had an apparent disease-free interval (ADFI) of < 8 weeks. By comparison, dogs in which predisposing disorders were corrected or those that were treated with low-dose, long-term antibiotic regimens subjectively had better control.     

Urinary tract infections in cats with hyperthyroidism, diabetes mellitus and chronic kidney disease

The prevalence of urinary tract infections (UTIs) in cats with hyperthyroidism (n=90), diabetes mellitus (DM) (n=57) and chronic kidney disease (CKD) (n=77) was evaluated retrospectively. It was found to be 12% in cats with hyperthyroidism and DM, respectively, and 22% in cats with CKD. Associations between UTIs and clinical signs, biochemical markers in serum and urinalyses were investigated. Many of the cats with UTIs had no clinical signs of lower urinary tract disease or changes in their laboratory values indicative of infection. Therefore, a urinalysis alone should not be used to exclude UTIs in these cats. UTIs are relatively common in cats with hyperthyroidism, DM and CKD, and urine cultures are recommended as part of the basic diagnostic plan for cats suspected of suffering from these conditions.     

Frequency of urinary tract infection in catheterized dogs and comparison of bacterial culture and susceptibility testing results for catheterized and noncatheterized dogs with urinary tract infections

OBJECTIVE: To determine frequency of urinary tract infections (UTIs) in catheterized dogs that had intervertebral disk disease (IVDD) or disease other than IVDD and compare bacterial culture and susceptibility testing results for catheterized and noncatheterized dogs with UTIs. DESIGN: Retrospective cohort study. ANIMALS: 147 catheterized dogs (105 with IVDD and 42 with other diseases) and 99 noncatheterized dogs with UTIs. PROCEDURES: Medical records were reviewed for signalment, history, clinical problem, duration of urinary tract catheterization, administration of drugs, and urine bacterial culture and susceptibility testing results. RESULTS: Forty-two percent (44/105) of dogs with IVDD and 55% (23/42) of dogs with other diseases had UTIs; this difference was not significant. For catheterized dogs, the odds of UTI were increased by 20% for each year increase in age, 27% for each day increase in duration of catheterization, and 454% with antimicrobial administration. Escherichia coli and Proteus spp were more frequently isolated from noncatheterized dogs, whereas Enterobacter spp and Staphylococcus spp were more frequently isolated from catheterized dogs. There was no significant difference in frequency of 1, 2, or 3 isolates between groups. Proportions of antimicrobials to which the most frequently isolated bacteria were resistant were not significantly different between groups. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that urinary tract catheterization is a reasonable alternative for management of dogs with urinary bladder dysfunction, but that duration of catheterization should be minimized and indiscriminate antimicrobial administration to dogs with indwelling urinary catheters should be avoided.     

Evaluation of catheter-associated urinary tract infections and multi-drug-resistant Escherichia coli isolates from the urine of dogs with indwelling urinary catheters

OBJECTIVE: To determine the frequency of urinary tract infections (UTIs) in dogs with indwelling urinary catheters in an intensive care unit (ICU) and the frequency of multi-drug-resistant (MDR) Escherichia coli UTIs in those dogs. DESIGN: Prospective study. ANIMALS: All dogs in the ICU with an indwelling urinary catheter from January 2003 through December 2003. PROCEDURES: Urine samples and rectal swab specimens were collected at admission and every 3 days until discharge from the hospital. Escherichia coli isolates from urine samples and rectal swab specimens and those from dogs that were temporally or spatially associated with dogs with MDR E coli UTIs underwent antimicrobial susceptibility testing. Pulsed-field gel electrophoresis was performed on MDR isolates from urine and rectal swab specimens. RESULTS: Urinary catheters were placed in 137 dogs. Twenty-six UTIs were diagnosed, 15 on the day of admission and 11 after 3 or more days of catheterization. Of 12 dogs with E coli UTIs, 6 were infected at admission and 6 acquired the infection in the ICU. Two MDR E coli UTIs were detected, 1 of which was acquired in the ICU. One MDR E coli urinary isolate had an electrophoresis pattern similar to that of rectal isolates from the same dog. Urinary E coli isolates were most frequently resistant to ampicillin and cephalothin. CONCLUSIONS AND CLINICAL RELEVANCE: The ICU-acquired MDR E coli UTI likely originated from the dog's intestinal flora during hospitalization. Dogs that have been referred from a community practice may have MDR E coli UTIs at the time of admission.     

Interrelations of organism prevalence, specimen collection method, and host age, sex, and breed among 8,354 canine urinary tract infections (1969-1995)

Selected information was compiled from canine urinalyses and urine cultures conducted between January 1969 and December 1995. Eight thousand three hundred fifty-four microbial isolates (bacteria and fungi) included 4,873 isolates from females and 3,481 from males. Ten bacterial genera accounted for 96.3% of the urinary isolates, including Escherichia coli (44.1%), Staphylococcus spp. (11.6%), Proteus spp. (9.3%), Klebsiella spp. (9.1%), Enterococcus spp. (8.0%), and Streptococcus spp. (5.4%) as the 6 most common isolates in both genders of dogs. Among these 6 genera, female dogs were generally predisposed over males, although males had more urinary tract infections (UTIs) caused by Klebsiella spp. Distributions of ages at UTI diagnosis tended to be similar between genders. Infection with a single microbial species was responsible for >72% of UTIs in both genders. Among females, 40 breeds and a mixed-breed group represented 90.2% of all positive urine cultures, 88.4% of the individual dogs with UTIs. and 88.2% of the microbial isolations. Among males, these same 41 breed groups represented 87.9% of all positive urine cultures, 87.6% of the individual dogs, and 88.2% of the microbial isolations.     

Clinical evaluation of a leukocyte esterase test-strip for detection of feline pyuria

Commercial macroscopic test-strips (dipsticks) that indirectly detect urine leukocytes by quantifying leukocyte esterase (LE) activity have been advocated as a simple, rapid, and inexpensive alternative to microscopic examination for detection of significant pyuria in urine specimens. The purpose of this study was to evaluate the diagnostic performance of a commercial LE test-strip for detection of feline pyuria. Two hundred and thirteen consecutive urine specimens were collected from 188 different feline patients and analyzed for LE activity with a LE test-strip (Multistix 2 Reagent Strips:Ames Division, Bayer Corp., Elkhart, IN). Results of the LE test-strip were compared with those of standard urine biochemical and microscopic sediment evaluations. Compared with urine sediment leukocyte counts, the LE test-strip had a sensitivity of 77%, a specificity of 34%, positive and negative predictive values of 14 and 91 % respectively, and an overall test efficiency of 39%. Multivariable logistic regression analysis did not reveal significant associations between pyuria (>5 WBC/hpf) and a positive LE test- strip reaction; however, hematuria, lipiduria, increasing age, and decreasing urine specific gravity were associated with a significantly increased risk for positive LE test-strip reactions. We conclude that the LE test-strip evaluated in this study is highly nonspecific for detection of significant pyuria in feline urine specimens and should not replace routine microscopic urine sediment examination in this species.     

Bacteriuria in cats with feline lower urinary tract disease: a clinical study of 134 cases in Norway

Feline lower urinary tract disease (FLUTD) is considered to be one of the most common diagnoses in feline patients. Several authors have concluded that feline idiopathic cystitis is the most common cause of FLUTD, whereas infectious cystitis is diagnosed in only 2% of the cases. In the period from January 2003 to February 2005, 134 cats that presented with signs of lower urinary tract disorders were included in a study at the Norwegian School of Veterinary Science. Ninety-seven percent were first opinion cases. All the cats went through a physical examination, and blood samples were collected for haematology and clinical chemistry. The urine analysis included urine stix, specific gravity, microscopic examination of the sediment and microbiological culturing. The urine samples were collected as voided mid-stream urine samples, by catheter or by cystocentesis and the method used was registered. Of the 134 cats included in the study, 37% were diagnosed as having obstructive and 63% as having non-obstructive FLUTD. In total 44 cats (33%) were diagnosed with bacteriuria, exceeding 10(3) colony forming units per millilitre (cfu/ml) and 33 (25%) of these cats had bacterial growth exceeding 10(4) cfu/ml, either alone or in combination with crystals and/or uroliths. Six cats (18%) with bacterial growth exceeding 10(4) cfu/ml were older than 8 years. No significant difference was found between the sampling methods performed with regard to bacteriuria. This study indicates that bacteriuria may have been underdiagnosed in Norwegian cats with clinical signs of FLUTD. It also confirms the importance of microbiological culturing in first opinion cases with FLUTD and that a skilled operator can get representative samples regardless the choice of method.     

Prevalence of Urinary Tract Infection in Dogs after Surgery for Thoracolumbar Intervertebral Disc Extrusion

Background: Urinary tract infection (UTI) is a common complication in people with spinal cord injury (SCI). Dogs with acute intervertebral disc extrusion (IVDE) have similar risk factors for UTI when compared with human SCI patients and have a high perioperative prevalence of UTI. Objectives: Determine the prevalence of UTI in dogs for 3 months after surgery for thoracolumbar IVDE and identify risk factors for development of UTI. Animals: Twenty‐five dogs treated surgically for 26 acute disc extrusions. Methods: Prospective study. Urinalysis and urine culture were performed perioperatively. At home, owners monitored urine with dipsticks every 48 hours for 1 month then once a week until 3 months. Dogs returned for assessment of motor function, urinalysis, and urine culture at 1 and 3 months after surgery. Presence of UTI over the 3‐month period was correlated to potential risk factors. Results: Ten dogs (38%) developed 12 UTIs over the 3‐month period, with the majority occurring between weeks 1 and 6; 60% of the UTIs were occult. Hematuria in the absence of pyuria or UTI was a common finding in the perioperative period. Sex, breed, and ambulatory status influenced the risk of developing a UTI. Conclusions and Clinical Importance: There is a high prevalence of UTIs, many of which are occult, in the 3 months after surgery for thoracolumbar IVDE. These dogs should be routinely monitored for UTI with urine culture regardless of urinalysis results.     

In vitro antimicrobial activity of nitrofurantoin against Escherichia coli and Staphylococcus pseudintermedius isolated from dogs and cats

Minimum inhibitory concentrations (MIC) of nitrofurantoin were determined by agar dilution in 269 canine and feline isolates of Escherichia coli and Staphylococcus pseudintermedius, two of the most common bacterial species associated with urinary tract infection (UTI) in small animals. The MIC90 for E. coli and S. pseudintermedius were 32 and 16 μg/ml, respectively. All isolates, including multidrug-resistant strains of known genetic background, displayed MICs below the drug concentrations reported in canine urine following oral administration of nitrofurantoin. Preliminary data on mutant prevention concentration (MPC) and many years of nitrofurantoin usage in human medicine suggest that emergence of resistant mutants during treatment is not a critical issue for this drug. The study provides species-specific data on nitrofurantoin MIC distribution that can be used for setting dog- and cat-specific breakpoints. Although nitrofurantoin is not an appropriate first-line agent for empirical treatment of canine UTI due to toxicity and poor pharmacokinetic properties, it may be indicated for treatment of UTI caused by multidrug-resistant bacteria, which are otherwise difficult to treat using conventional veterinary antimicrobial agents.     

Antimicrobial Susceptibility Patterns in Urinary Tract Infections in Dogs (2010–2013)

Background

Urinary tract infections (UTIs) are common in dogs. The responsible bacterial populations have evolved with increasing resistance to many antimicrobials.

Objective

To characterize the antimicrobial susceptibility patterns of canine urinary tract isolates over a 51‐month period.

Animals

One thousand six hundred and thirty‐six bacterial isolates from 1,028 dogs.

Methods

Aerobic bacterial isolate growth and susceptibility data from urine cultures of dogs were identified, retrospectively. Medical records were reviewed to obtain signalment, comorbidities, and antimicrobial use in the previous 30 days. The UTIs were further categorized as uncomplicated, complicated, or pyelonephritis.

Results

Common bacterial isolates identified were Escherichia coli (52.5%), Staphylococcus spp. (13.6%), and Enterococcus spp. (13.3%). In vitro susceptibility among all isolates varied for commonly prescribed antimicrobials (amoxicillin [59%], amoxicillin/clavulanic acid [76%], cephalexin [66%], enrofloxacin [74%] and trimethoprim‐sulfamethoxazole [86%]). For all antimicrobials tested (except aminoglycosides), in vitro susceptibility was higher in uncomplicated versus complicated infections (P < .05). Uncomplicated infection isolate susceptibility rates remained ≤90% for PO administered antimicrobials. Administration of amoxicillin, doxycycline, and enrofloxacin, but not amoxicillin/clavulanic acid in the previous 30 days was associated with resistance to that antimicrobial. Multidrug resistant isolates of E. coli and Staphylococcus spp. were more common in dogs with complicated than uncomplicated UTIs (36% versus 21%, P < .0001).

Conclusions and Clinical Importance

In vitro susceptibility was highly variable and no PO administered antimicrobial had >90% efficacy among isolates tested. Multidrug resistance was frequent among isolates tested suggesting that routine culture and susceptibility testing is indicated. Previously prescribed antimicrobials may affect empirical choices made pending susceptibility testing.     

Thinking outside the box: feline elimination

Feline elimination problems are the leading behavioral complaint of cat owners. When presented with a feline elimination problem there are three main diagnostic categories: medical problems, marking or toileting problems. It is important to first perform diagnostic tests to rule out and/or address underlying medical issues and all feline house soiling patients should receive a comprehensive physical examination. When the elimination problem persists after a medical problem has either been ruled out or remedied, a behavioral diagnosis should be obtained. The primary distinction that must be made in a behavioral diagnosis is whether the cat is engaging in marking behavior or selecting a spot other than the litterbox for elimination (a toileting problem). The motivation for urine marking may be territorial behavior or anxiety/stress whereas toileting problems are often triggered by medical causes, aversions, preferences or anxiety. Marking animals should be neutered and additional treatment measures may include reducing conflict and stress in the environment. Drug therapy has been long used to help control urine marking and recent studies have furthered our knowledge about the most appropriate treatments. Treatment for toileting problems should focus on providing an attractive litterbox while reducing the attractiveness or accessibility of inappropriate target spots.     

Retrospective evaluation of urinary tract infection in 42 dogs with hyperadrenocorticism or diabetes mellitus or both

A retrospective study was performed to determine the proportion of dogs with hyperadrenocorticism or diabetes mellitus or both that had urinary tract infection (UTI) and to describe clinical and laboratory findings. Dogs with these endocrine disorders were included if results of quantitative urine culture were available and dogs were not receiving antimicrobials. Dogs with positive urine cultures were considered to have UTI and dogs with negative urine cultures were used as controls. Information including history, clinical signs, physical examination findings, and results of laboratory tests and urine culture was extracted from all records. Findings in dogs with UTI were compared with control dogs. There were 101 dogs with hyperadrenocorticism or diabetes mellitus or both that met inclusion criteria; 42 (41.6%) had UTI and 59 (58.4%) did not. UTI was present in 46% of dogs with hyperadrenocorticism, 37% of dogs with diabetes mellitus, and 50% of dogs with both endocrine disorders. There was no association between endocrine group and occurrence of UTI. Escherichia coli was the most common bacteria isolated, and cultures from 29 dogs (69%) showed growth of this organism. Of dogs with UTI, <5% had stranguria, pollakiuria, or discolored urine, whereas 60% had pyuria and 69% had bacteriuria. We conclude that UTIs are common in dogs with hyperadrenocorticism, diabetes mellitus, or both diseases. Clinical signs of UTI, however, are uncommon and results of urinalysis may be normal. Therefore, it is appropriate to recommend urine culture as part of the evaluation of dogs with these endocrine disorders.