UA & Microbio Summary

EVALUATION FOR BACTERIAL OR YEAST OTITIS

Sample Collection Method

  1. Cotton-Tipped Applicator Usage: Insert a cotton-tipped applicator into the otic canal and gently rotate to remove debris from the canal.

    • Sample Collection: Collect samples from both ears, and roll each sample onto a glass slide.
    • Time-Saving Tip: Roll samples from each ear onto the same slide to minimize the need to dip multiple slides. Conventionally, place the left ear sample on the left side of the slide and the right ear sample on the right side, ensuring clarity.
    • Sample Preparation: It is important to note that samples do NOT need to be heat fixed prior to staining.

  2. Staining Process: Stain the prepared slide using Diff-Quik stain and allow it to air dry.

  3. Initial Observation: Start scanning the stained slide using a 10X objective lens to identify representative areas. After finding suitable regions, switch to a 100X objective lens as yeast and bacteria typically localize around or are found atop clumps of keratinocytes.

  4. Estimation of Organisms: Carefully examine 5-10 areas to assess the quantity of infectious organisms present. It is considered normal to find:

    • 0-2 yeast per 40X field
    • 0-4 or 5 cocci per 40X field

Findings

  • Normal Ear Swab: Healthy keratinocytes along with beaded oily or waxy debris, with no infectious organisms present.
  • Typical Yeast Infection: Observations might include the presence of neutrophils, which could be scarce or absent. An example slide may show a single keratinocyte positioned within the field of view.

BACTERIAL AND YEAST IDENTIFICATION

Bacterial Morphology

  • Cocci and Rods: Both cocci (spherical bacteria) and rods (bacilli) are typically present in samples. Rods are noted to sometimes form elongated chains during infections.

  • Diplococci: Refers to certain strains of bacterial cocci that pair together, forming groups of two.

    • Cocci can be identified visually as purple dots under the microscope.

  • Yeast Appearance: Yeast can appear to have a footprint shape, indicating their individual structure and budding process. Yeast bodies can be classified as either budded or non-budded, with budding indicating active growth.

Inflammatory Response

  • Neutrophils: In samples, streaming neutrophils may be observed, which present as ribbons of nuclear material resulting from ruptured neutrophils. These findings are consistent with rod bacterial infections, often caused by Pseudomonas, which typically yield visibly yellow pus in affected ears. High concentrations of white blood cells, predominantly neutrophils, may appear intact or as strands of nuclear debris from disintegrated cells.

YEAST DERMATITIS

  • Sample Collection Method: A slide impression can be made, or clear acetate tape may be used to capture samples from dry skin.
    • In skin samples, finding even a couple of yeast cells suffices to diagnose yeast dermatitis, contrasting with ear cytology where occasional yeast presence is considered normal.
    • Inflamed skin samples are characteristically rich in neutrophils, and with prolonged inflammation, macrophages may be recruited to the area. The observed foamy macrophage may be noted as actively consuming a neutrophil.

DERMATOPHYTOSIS

Common Fungal Agents in Canine and Feline Patients

  • The three primary dermatophytes (fungi causing skin infections) observed in dogs and cats include:
    1. Microsporum canis: This is the most frequent dermatophyte causing ringworm in these animals and possesses the ability to fluoresce under a Wood's lamp.
    2. Microsporum gypseum: Does not fluoresce and is less commonly encountered.
    3. Trichophyton mentagrophytes: Generally does not fluoresce either.
  • Infection Routes: Animals can contract dermatophytes through contact with infected hair or scales, exposure to infected individuals, or coming into contact with contaminated soil or objects (fomites).
  • Hair Examination: To diagnose Microsporum canis, infected hairs may fluoresce when examined with a Wood's lamp. When sampling, pluck hair from around an observable lesion, then prepare it on a glass slide with a drop of mineral oil and cover with a slip for viewing under a 10X objective. Infected hairs exhibit a greater diameter than normal hairs because they are coated with fungal spores, creating a phenomenon known as ectothrix invasion characterized by the production of spores around the hair shafts.

URINARY CRYSTALS IN CANINES AND FELINES

Struvite Crystals

  • Chemical Composition: Also referred to as magnesium ammonium phosphate or triple phosphate, struvite crystals are most prevalent in canine and feline urine and can sometimes be found in normal urine.
  • Morphology: Struvite crystals are identifiable by their envelope shape, distinguishing them from calcium oxalate crystals which possess different characteristics. Struvite stones are formed by bacterial activity that breaks down urea into ammonium and phosphate, leading to increased urine pH.
  • Clinical Pearl: Almost all struvite stones in dogs result from a urease-positive bacterial infection. Management includes eliminating the underlying infection and implementing a dissolution diet that lowers urine pH. After successful dissolution of stones and resolution of urinary tract infections (UTI), dogs do not require ongoing special diets. In contrast, cats often develop sterile struvite stones and will benefit from long-term dietary management to maintain optimal urinary pH and minimize dietary ash content.

Calcium Oxalate Crystals

  • Types Identified: Calcium oxalate crystals can be categorized as dihydrate or monohydrate:

    • Dihydrate: Typically seen as square-shaped with intersecting lines and represent the most common form.
    • Monohydrate: Present as a dumbbell shape or, less commonly, a picket fence formation primarily associated with ethylene glycol toxicity.

  • Formation Factors: These crystals can manifest in normal urine but are more prevalent in cases of urine supersaturation with calcium. Pre-disposing factors include hypercalcemia due to conditions like hyperparathyroidism or lymphoma. Certain medications may increase calcium excretion, leading to crystallization. Miniature Schnauzers especially show a predisposition to form calcium oxalate stones. Picket fence shaped monohydrate crystals observed with acute kidney failure raise concerns for ethylene glycol toxicity.

Ammonium Biurate and Bilirubin Crystals

  • Ammonium Biurate: Characterized as yellow-brown irregularly shaped crystals with spiky projections, described metaphorically as 'thorny apples.' These are rarely observed in healthy dogs or cats except in certain predisposed breeds (e.g., Dalmatians, English Bulldogs). Liver disease may also elevate renal excretion of ammonium urate. Dietary management through a purine-restricted alkalinizing diet, such as U/D, can assist in dissolving urate stones. A notable statistic is that 60% of urate stones occur in Dalmatians.
  • Bilirubin Crystals: Commonly found in canine urine (sometimes present in healthy, concentrated samples) but are abnormal in felines, warranting investigation for potential liver disease.

Cystine Crystals

  • Genetic Basis: Cystine crystals arise from a genetic disorder affecting renal tubular reabsorption of cystine and other amino acids without compromising renal function. Cystine crystals exhibit a flat, hexagonal shape with six sides—distinct from struvite crystals, which may also be flat but have a different morphology.

Calcium Phosphate Crystals

  • Characterization: Calcium phosphate crystals manifest in neutral or alkaline urine. They are generally uncommon and may result from dietary excesses or metabolic conditions promoting elevated calcium levels, such as hyperparathyroidism.

COMMON AND UNCOMMON URINE CRYSTALS IN VETERINARY PRACTICE

  • Common Crystals:

    • Struvite
    • Bilirubin
    • Calcium Carbonate
    • Calcium Oxalate dihydrate
    • Calcium Oxalate monohydrate (including dumbbell and hemp seed forms).

  • Uncommon Crystals:

    • Ammonium biurate
    • Cystine

URINALYSIS IN CANINES AND FELINES

Dipstick Evaluation and General Principles

  • Renal analysis begins with the assessment of a urine dipstick. Key insight: the test pads for urine specific gravity, urobilinogen, nitrate, and leukocytes do not provide reliable results in veterinary contexts.
  • pH Measurement: Normal urine pH values range from 6 to 7.5. Values exceeding 7.5 may indicate urinary infections involving urease-producing bacteria and necessitate deeper investigation for infection markers.
  • Protein Content: In healthy urine, protein content should be minimal. The kidneys' filtration units (glomeruli) usually prevent the passage of substantial plasma proteins (e.g., albumin and globulin). A negative test result is considered reliable, although false positives can occur. For cases with persistent positive protein results, urine protein concentration can be further quantified using the urine protein:creatinine ratio; normal values are UPC <0.5 for dogs and UPC <0.4 for cats.
  • Blood Testing: This dipstick test can identify heme-containing substances such as lysed red blood cells or myoglobin from muscular damage, which should be further corroborated with urine sediment analysis.
  • Bilirubin Detection: In