New skin test to find bacteria on dogs with skin disease

Abstract

BACKGROUND: Cytological examination of the skin is an important diagnostic technique in dermatology for disease diagnosis and monitoring of treatment. Impression smear and tape-strip preparation are gold standard cytological techniques. This study introduces a novel cytological method, slurry preparation, in which debris collected from the skin surface is macerated in warm sterile water and dried on the slide. HYPOTHESIS/OBJECTIVES: To compare organism yield between a novel and two standard cytological collection techniques by evaluating bacteria and Malassezia yeast counts. ANIMALS: Thirty client-owned dogs diagnosed with atopic dermatitis and lesions consistent with pyoderma and/or Malassezia dermatitis. MATERIALS AND METHODS: In a prospective, blinded comparison study, dermatological lesions from each dog were sampled using impression smear, tape-strip and slurry preparation methodologies. Ten random reticle fields per lesion, accounting for a total area of 6.25 × 10 mm(equivalent to ˜5% of a typical ×40 field), were evaluated by light microscopy for each cytological method. Bacterial and Malassezia organisms were measured as counts/sample. The slurry preparation was compared to each of the standard methodologies separately using paired Student's t-tests. RESULTS: The slurry preparation was demonstrated to be more sensitive than gold standard techniques in detecting bacteria, with mean differences of 12.7 and 13.5 additional bacteria per cytological sample, compared to the impression and tape-strip preparations, respectively. The slurry preparation did not differ significantly in detecting Malassezia organisms compared with impression smear preparation. The tape-strip preparation was demonstrated to be more sensitive than the slurry preparation in the detection of Malassezia organisms, finding a mean difference of 0.22 more organisms per sample. CONCLUSION: Slurry preparation presents advantages over the gold standard techniques in the detection of bacteria which can help to manage canine pyoderma more appropriately. Performing a slurry preparation in cases of suspected canine pyoderma could be considered as an alternative to the gold standard techniques.