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

Abstract

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&#x2009;canis infection in cats. ANIMALS: Forty Persian cats. METHODS AND MATERIALS: Hair and scale samples were collected by combing the coat using a 5&#x2009;&#xd7;&#x2009;5&#x2009;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&#x2009;h (n&#x2009;=&#x2009;10); Group 2: 24&#x2009;h (n&#x2009;=&#x2009;10); Group 3: 48&#x2009;h (n&#x2009;=&#x2009;10); and Group 4: 72&#x2009;h (n&#x2009;=&#x2009;10). Cultures were compared regarding the degree of fungal invasion by either M.&#x2009;canis or nondermatophytic contaminant moulds (NDM). RESULTS: Processing samples after 24&#x2009;h of storage resulted in increased isolation rates of NDM and decreased isolation rates of M.&#x2009;canis. Samples processed after 48&#x2009;h and 72&#x2009;h presented more than half of the plates with a high degree of fungal contamination (i.e. NDM occupying &#x2265;50% of the total fungal mass). However, samples processed after 8&#x2009;h and 24&#x2009;h presented a lower degree (P&#x2009;<&#x2009;0.05) of NDM plate invasion and higher recovery rates of M.&#x2009;canis when compared to samples processed after 48&#x2009;h and 72&#x2009;h. CONCLUSIONS AND CLINICAL IMPORTANCE: Delayed processing time is closely associated with the overgrowth of contaminants and with lower recovery rates of M.&#x2009;canis.