Onychomycosis: clinical,mycological and in vitro susceptibility testing of isolates of Trichophyton rubrum

BACKGROUND

Onychomycosis or nail fungal infection is the most common nail disease.Despite the wide range of studies on this condition, it remains difficult toestablish the correct diagnosis and effective treatment.

OBJECTIVES

To evaluate the efficacy of classical laboratory methods for the diagnosisof onychomycosis, and the in vitro susceptibility of the its mainetiological agent to antifungals used in routine.

METHODS

Nail samples of 100 patients with clinically suspected feet onychomycosiswere collected to confirm the diagnosis by direct mycological examinationand fungal culture. In vitro antifungal susceptibility testing was performedagainst strains of the main dermatophyte isolated by microdilution,according to the standardized protocol (M38-A2 - CLSI)

RESULTS

Clinical diagnosis of onychomycosis was confirmed by laboratory analysis in59% of patients. Of these, 54.2% were positive only in direct mycologicalexamination, 44.1% in direct mycological examination and culture, and onecase (1.7%) was positive only in culture, resulting in weak agreementbetween these tests (Kappa = 0.385; p <0.001) High minimum inhibitoryconcentration values of fluconazole and itraconazole were observed in 66.7%and 25.0% of isolates of T. rubrum tested. Additionally,high MIC values of terbinafine and ciclopirox was detected in only oneisolate, and this was one of the strains in which in vitro activity ofitraconazole and fluconazole has not been proven.

CONCLUSIONS

Poor agreement was observed between direct mycological examination andculture for the diagnosis of onychomycosis, with direct mycologicalexamination being significantly more sensitive. Except for fluconazole, theother three antifungals tested showed good in vitro activity againstclinical isolates of T. rubrum.