The influence of sample processing time on the performance of Microsporum canis cultures in cats

BACKGROUND

Fungal culture is widely used as a diagnostic tool for detecting dermatophytosis. However, the presence of fungal contaminants can influence the culture's performance and compromise the diagnosis.

OBJECTIVE

To verify whether the sample processing time can affect the performance of fungal culture for the diagnosis of Microsporum canis infection in cats.

ANIMALS

Forty Persian cats.

METHODS AND MATERIALS

Hair and scale samples were collected by combing the coat using a 5 × 5 cm sterile polyester carpet. The carpets were assigned randomly to four groups based on time point of processing samples after collection (i.e. used for culture on a selective agar medium for dermatophytes): Group 1: 8 h (n = 10); Group 2: 24 h (n = 10); Group 3: 48 h (n = 10); and Group 4: 72 h (n = 10). Cultures were compared regarding the degree of fungal invasion by either M. canis or nondermatophytic contaminant moulds (NDM).

RESULTS

Processing samples after 24 h of storage resulted in increased isolation rates of NDM and decreased isolation rates of M. canis. Samples processed after 48 h and 72 h presented more than half of the plates with a high degree of fungal contamination (i.e. NDM occupying ≥50% of the total fungal mass). However, samples processed after 8 h and 24 h presented a lower degree (P < 0.05) of NDM plate invasion and higher recovery rates of M. canis when compared to samples processed after 48 h and 72 h.

CONCLUSIONS AND CLINICAL IMPORTANCE

Delayed processing time is closely associated with the overgrowth of contaminants and with lower recovery rates of M. canis.

Comparison of carpet and toothbrush techniques for the detection of Microsporum canis in cats

OBJECTIVES

The aim of this study was to evaluate the diagnostic concordance between the toothbrush and carpet techniques for the detection of Microsporum canis in cats in a field study.

METHODS

Thirty-nine Persian cats from a cattery were used. Fungal culture samples from the haircoat of each cat were collected by stroking the coat with a sterile toothbrush and a 5 × 5 cm-sized sterile carpet square (n = 78 total samples). Specimens were inoculated onto Mycosel Agar and incubated at 25°C for 21 days. Both techniques were compared using the following parameters: number of plates without fungal growth, number of plates with contaminant growth and number of plates positive for dermatophytes.

RESULTS

The feline population in the study cattery was 39. Thirty (77%) were symptomatic and nine (23%) asymptomatic. The diagnosis was made via carpet and toothbrush methods and 78 cultures were performed. On day 21, M canis was detected in all culture plates. No contaminant molds were observed.

CONCLUSIONS AND RELEVANCE

The concordance rate between the carpet and toothbrush techniques among the 78 evaluable culture plates was 100%. Both methods are equally effective for collecting material for M canis culture. Additionally, both techniques are inexpensive and easy to perform in feline clinical practice.