Week 6 Lesson 48 Lower Urinary Tract Infections – Diagnostic Testing

Systems 2: Urinary Tract and Water Balance

  • Lower Urinary Tract Infections – Diagnostic Testing

  • Dr. Sharianne Suepaul

  • ERSITAS, St. George's University, School of Veterinary Medicine, Grenada, West Indies

Pre-work Learning Outcomes

  • By the end of this session, students will be able to:

    • Identify diagnostic methods for bacterial UTIs.

    • Identify urine collection techniques for bacteriological culture of urine.

    • Describe urine collection techniques for bacteriological culture of urine.

Diagnosis of Bacterial UTIs

  • Methods Used:

    • Observation of Clinical Signs:

      • Assess symptoms and behavioral signs.

    • Urinalysis:

      • Examines properties of urine: color, turbidity, pH, specific gravity.

      • Detects compounds: blood, proteins, sugars, ketones, bilirubin.

      • Sediment analysis: looks for white blood cells, red blood cells, bacteria, crystals, renal casts.

    • Quantitative Urine Culture and Antimicrobial Sensitivity Testing:

      • Identifies bacterial species causing infection.

      • Determines effective antibiotics for treatment.

    • Molecular Techniques:

      • Polymerase Chain Reaction (PCR)

      • Next-generation sequencing techniques

    • Other Tests:

      • Blood tests may support UTI diagnosis.

      • X-rays or ultrasounds for further examination.

Urine Collection Techniques and Considerations

  • Sample Storage and Transportation:

    • Transport samples to lab within 24 hours; voided samples within 2 hours.

    • Refrigerate samples at 4°C.

    • Use tubes with preservatives for longer transportation (not ideal practice); requires adequate volume.

    • Proper labeling and containment to avoid contamination.

In-Class Learning Outcomes

  • At the end of this session, students will be able to:

    • Evaluate urine collection techniques.

    • Describe urine transportation and preservation.

    • Discuss the microbiome of the urinary tract.

    • Explain the rationale for antimicrobial susceptibility testing.

Guidelines on Urine Culture Sampling

  • When to Collect:

    • Aerobic bacterial urine culture is preferred for suspected bacterial cystitis.

    • In dogs with sporadic cystitis and limited previous antimicrobial exposure, empirical therapy may be justified.

    • For cats, always confirm bacterial cystitis through culture due to frequent non-bacterial conditions.

Treatment Considerations

  • Common Empirical Treatment Drugs:

    • Amoxicillin

    • Trimethoprim-sulphamethoxazole

    • Treatment duration typically 3-5 days.

    • Reserve stronger antibiotics (e.g. fluoroquinolones) for specific cases.

Quantitative Culture of Urine

  • Process:

    • Incubation of aerobic bacterial cultures for 24-48 hours.

    • Counting colonies for quantitative analysis.

Laboratory Culture Techniques

  • Materials for Culture:

    • Requires calibrated loop (0.001 ml) and culture plates (e.g. Blood Agar, MacConkey Agar).

    • Incubate and assess colony growth.

Results Interpretation

  • CFU Measurements:

    • Quantitative results are measured in colony-forming units (CFUs/ml).

    • Interpretation for infection depends on CFU count and collection method.

Antimicrobial Susceptibility Testing (AST)

  • Purpose:

    • Evaluate bacterial growth inhibition by antimicrobial drugs.

  • Methods:

    • Disc diffusion methods (e.g., Kirby-Bauer).

    • Zone of inhibition measured to determine susceptibility.

    • Broth dilution techniques for MIC determination.

Challenges in AST Results

  • Factors affecting treatment success:

    • Host immune status, location of infection, presence of biofilm, and residual antimicrobials.

Antimicrobial Treatment Considerations

  • Assess antibiotic penetration into urine and compare with MIC values for pathogens.

  • Include patient factors such as chronicity and cost in decisions for antimicrobial use.

Conclusion

  • Understand the significance of urine collection methods and their implications on UTI diagnosis and treatment.

  • Discuss the relevance of next-generation sequencing in identifying UTI causative agents.

References

  • Veterinary Microbiology and Microbial Disease, 2nd edition

  • Clinical Veterinary Microbiology, 2nd Edition

  • American Society for Microbiology, Kirby-Bauer Disk Diffusion Test Protocol

Questions

  • Contact Dr. Suepaul for inquiries: ssuepaul@sgu.edu.

Systems 2: Urinary Tract and Water Balance

Lower Urinary Tract Infections – Diagnostic Testing

Dr. Sharianne SuepaulERSITAS, St. George's University, School of Veterinary Medicine, Grenada, West Indies

Pre-work Learning Outcomes

By the end of this session, students will be able to:

  • Identify various diagnostic methods for bacterial urinary tract infections (UTIs) in animals.

  • Explain the appropriate urine collection techniques for the bacteriological culture of urine, including indications and potential pitfalls.

  • Describe in detail the methods for urine collection that ensure accurate diagnostic results in veterinary practice.

Diagnosis of Bacterial UTIs

Methods Used:

  1. Observation of Clinical Signs:

    • Carefully assess and document symptoms such as inappropriate urination, increased frequency of urination, straining to urinate, and changes in appetite or behavior that suggest discomfort.

  2. Urinalysis:

    • Conduct a thorough examination of urine properties, including color (e.g., pale yellow to amber), turbidity (clear vs. cloudy), pH levels (normal range is usually 6.0-7.5), and specific gravity (normal range is typically 1.012-1.030).

    • Detect and analyze the presence of abnormal compounds:

      • Blood (hematuria)

      • Proteins (proteinuria)

      • Sugars (glucosuria)

      • Ketones (indicative of metabolic disorders)

      • Bilirubin (may indicate liver issues)

    • Sediment analysis includes searching for white blood cells (inflammation), red blood cells (hemorrhage), bacteria (infection), crystals (potential urinary stones), and renal casts (kidney disease).

  3. Quantitative Urine Culture and Antimicrobial Sensitivity Testing:

    • Perform urine cultures to identify bacterial species responsible for the UTI. It is crucial for determining antimicrobial sensitivity to guide effective treatment.

  4. Molecular Techniques:

    • Employ advanced diagnostic methods such as Polymerase Chain Reaction (PCR) for identifying specific pathogens, which provides quicker and more accurate results compared to traditional culture methods, and Next-Generation Sequencing Techniques for comprehensive microbial profiling.

  5. Other Tests:

    • Consider additional blood tests to provide supportive data for UTI diagnosis, as well as imaging tests like X-rays or ultrasounds to examine urinary anatomy and rule out anatomical abnormalities or obstructions.

Urine Collection Techniques and Considerations

Sample Storage and Transportation:

  • To ensure accuracy, transport samples to the laboratory within 24 hours of collection; however, voided samples should ideally reach the lab within 2 hours.

  • For sample integrity, refrigerate samples at 4°C until analysis.

  • If extended transport is necessary, use tubes with preservatives cautiously, as this is not ideal practice and requires an adequate volume for subsequent testing.

  • Ensure proper labeling and containment to avoid contamination and misidentification.

In-Class Learning Outcomes

At the end of this session, students will be able to:

  • Evaluate and compare different urine collection techniques for effectiveness and reliability.

  • Describe the procedures and best practices for urine transportation and preservation to maintain sample quality.

  • Discuss the microbiome of the urinary tract and its role in health and disease.

  • Explain the significance of antimicrobial susceptibility testing in formulating effective treatment plans for UTIs.

Guidelines on Urine Culture Sampling

When to Collect:

  • An aerobic bacterial urine culture is preferred for diagnosing suspected bacterial cystitis.

  • In cases of dogs with sporadic cystitis and a history of limited previous antimicrobial exposure, empirical therapy may be justified in specific scenarios.

  • For cats, it is always essential first to confirm bacterial cystitis through culture due to the common occurrence of non-bacterial urinary conditions.

Treatment Considerations

Common Empirical Treatment Drugs:

  • Amoxicillin

  • Trimethoprim-sulphamethoxazole

  • Treatment duration typically spans 3-5 days, emphasizing the importance of following established guidelines based on culture results.

  • Reserve stronger antibiotics (e.g., fluoroquinolones) for specific cases where first-line treatments fail or if the patient has recurrent infections.

Quantitative Culture of Urine

Process:

  • The process involves the incubation of aerobic bacterial cultures for a duration of 24-48 hours.

  • An accurate counting of colonies is vital for quantitative analysis, significantly affecting treatment decisions.

Laboratory Culture Techniques

Materials for Culture:

  • Requires a calibrated loop (0.001 ml) for accurate sampling and culture plates, such as Blood Agar and MacConkey Agar, to support various bacterial growth.

  • Proper incubation conditions and assessment for colony growth are fundamental for accurate diagnosis.

Results Interpretation:

  • CFU Measurements: Quantitative results from cultures are expressed in colony-forming units (CFUs/ml), which should be interpreted considering both the CFU count and the urine collection method used. This aids in diagnosing possible infections accurately.

Antimicrobial Susceptibility Testing (AST)

Purpose:

  • Evaluate the effectiveness of antimicrobial drugs against bacterial growth, guiding proper treatment options.

Methods:

  • Disc diffusion methods (e.g., Kirby-Bauer) for assessing susceptibility.

  • Measurements of the zone of inhibition are used to determine the susceptibility results.

  • Broth dilution techniques are utilized for Minimum Inhibitory Concentration (MIC) determination, which defines the lowest concentration of the drug needed to inhibit bacterial growth.

Challenges in AST Results

Factors affecting treatment success:

  • Considerations include the host's immune status, the anatomical location of infection, the presence of biofilm, and residual antimicrobials from prior treatments.

Antimicrobial Treatment Considerations

  • Assess the penetration of antibiotics into urine and compare it with MIC values for pathogens to ensure therapeutic effectiveness.

  • Include patient-specific factors such as the chronicity of the infection and cost considerations when making decisions regarding antimicrobial use.

Conclusion

  • Understand the significance of urine collection methods and their implications on UTI diagnosis and treatment outcomes.

  • Highlight the relevance of next-generation sequencing in accurately identifying UTI causative agents and its potential impact on future treatment strategies.

References

  • Veterinary Microbiology and Microbial Disease, 2nd edition

  • Clinical Veterinary Microbiology, 2nd Edition

  • American Society for Microbiology, Kirby-Bauer Disk Diffusion Test Protocol

Questions

For any inquiries, please contact Dr. Suepaul at ssuepaul@sgu.edu.