Comparação da técnica de microdiluição em caldo e ETEST para o cetoconazol frente à Malassezia pachydermatis

Abstract

Malassezia pachydermatis is recognized as a normal inhabitant and an opportunistic pathogen of the external ear canal and skin of dogs and cats. In special clinical conditions, and mainly in the cases of therapeutic failure related to external otitis and dermatitis complicated by this yeast, is recommended testing susceptibility to antifungal drugs. Different approaches of evaluating the susceptibility of yeasts faced to antifungals in laboratory exist, some of them are commercial approaches and others previously standardized by the CLSI (NCCLS, 2002). The purpose of this study was to evaluate the susceptibility of 17 samples of M. pachydermatis from canine external otitis using two different in vitro antifungal susceptibility methods: the Etest ® and the broth Microdilution Method (MD) with ketoconazole. The mean MIC observed between the 17 samples were 0.103mg/mL to ETEST and 0.0012mg/mL to MD ranging from 0.004 to 0.75mg/ mL in ETEST and 0.0019 and 0.03mg/mL in MD using the same samples. By ETEST, two (11.8%) samples were resistant, eight (47.1%) susceptible and seven (41.1%) showed intermediate susceptibility. Through the MD it was observed four (23.5%) resistant samples, seven (41.2%) susceptible and six (35.3%) samples with intermediate susceptibility. Despite of the percentages being equivalent in each rank of susceptibility through the two techniques, the results do not correspond to the same sample. These results showed that there is an urgent need to standardize those values considered as parameters for growth inhibition of this yeast. Then a simple and efficient method could be used routinely in the laboratory practice.

Antifungal Resistance Regarding Malassezia pachydermatis: Where Are We Now?

“…Some studies [21][22][23][24][49][50][51]58,59,61,62,67,70,86,87] evaluating the antifungal susceptibility of M. pachydermatis reported variable percentages of isolates resistant to various agents (Document S1) based on different interpretive breakpoints. However, in none of these studies were the in vitro values correlated with the lack of response to therapy.…”

“…In some cases [21,22,58,59,61,62,67], breakpoints were selected taking into account the MIC 50 /MIC 90 values (MIC 50 and MIC 90 are the MICs required to inhibit the growth of at least 50% and 90% of the isolates tested, respectively. MIC 50 corresponds to the median).…”

“…Moreover, the percentage of resistant isolates would be fixed at no more than 10%, given that the MIC 90 encompasses at least 90% of the strains tested by definition. In this regard, how the percentage of resistant isolates in some studies [21,22,67] employing the MIC 50 /MIC 90 criterion could be over 10% is unclear (Document S1).…”

“…In particular, a standard procedure for in vitro susceptibility testing-which is essential in order to obtain reproducible and clinically significant measurements of antifungal activity-has not been developed yet [20]. Based on different in vitro tests, some studies have reported high resistance rates for various agents [21][22][23][24]. According to some authors, the appearance of resistant strains would be a concern [25], while a low azole susceptibility of the yeast would be a well-documented phenomenon [26].…”