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.