Evaluation of Antifungal Susceptibility Testing with Microdilution and Etest Methods of Candida Blood Isolates

Abstract

Candida species that show an increasing number of clinical and/or microbiological resistance to several antifungals and are the most common agents of invasive fungal infections. The aim of this study was to investigate the in vitro susceptibility of Candida blood isolates to antifungal agents (amphotericin B, fluconazole, itraconazole, and voriconazole) by comparative use of the CLSI reference microdilution method and Etest. Four hundred Candida blood isolates (215 Candida albicans, 185 non-albicans Candida strains) were included in the study. The broth microdilution test was performed according to the CLSI M27 A2 document. Etest was carried out according to the manufacturer's instructions. The MIC results obtained with reference microdilution were compared with those obtained with the Etest by using percent and categorical agreements. According to MIK(90) values, voriconazole was the most active and itraconazole was the least active drug in vitro against all Candida species. Other than voriconazole, statistically significant differences were found when the susceptibility of Candida albicans and non-albicans Candida spp. to amphotericin B, fluconazole, and itraconazole were compared. These antifungal agents were found to be more active to C. albicans. Among the non-albicans Candida species, the lowest MIC values were obtained for Candida parapsilosis isolates. When the standard method was compared with Etest, the total agreement was higher for C. albicans than for non-albicans species, especially for fluconazole and voriconazole. In view of the findings, it was concluded that itraconazole showed the lowest activity against all Candida species. Etest could be an alternative method in assessing the in vitro antifungal susceptibility of Candida spp., but it is more convenient to use the microdilution method for studying in vitro susceptibility of non-albicans species, in particular for those possessing high MIC values against azoles.

Species distribution and antifungal susceptibility profile of <i>Candida spp</i> isolated from urine of hospitalized patients in Dschang District Hospital, Cameroon

“…This observation is uncommon compared with almost all the previously reported studies that indicated some degree of sensitivity to amphotericin B. Although, in a study conducted by Ruan et al (2008), the resistance was extremely high against amphotericin B in C. krusei strains (95%) and in C. glabrata strains (53%), in recent years, the low rates of amphotericin B resistance have been reported in the C. albicans, C. glabrata, C. parapsilosis, C. tropicalis and C. krusei isolates (Metin et al, 2011;Taj-Aldeen et al, 2014).…”

Antifungal Susceptibly Testing by Concentration Gradient Strip Etest Method for Fungal Isolates: A Review

“…Nevertheless, the overall EA between the CLSI and Etest RPMI agar was mostly >96% within the acceptable ±2 dilution range (1994 to 2011) for the most prevalent Candida species (C. albicans, C. glabrata, C. parapsilosis, and C. tropicalis) [30,31,[34][35][36] and C. neoformans [37] (Table 1). The exceptions were the lower percentages of EA in one study where the Etest data were evaluated at both 24 and 48 h versus the CLSI method [38], for various species, including C. lusitaniae and C. neoformans [30,39]. The Etest was also evaluated for testing C. krusei with amphotericin B with an acceptable EA [30,34].…”

“…The published EA percentages between both CLSI and Etest fluconazole MICs for six species of Candida and C. neoformans [31,34,35,[38][39][40][41][42][43] and the EUCAST [25,32] are presented in Table 3. Although the EA for fluconazole was >90% versus the Etest data for Candida spp.…”

Identification and Antifungal Susceptibility Patterns of Candida Strains Isolated From Blood Specimens in Iran

“…Nevertheless, other Candida species have emerged as clinically important opportunistic pathogens (3)(4)(5)(6). Resistance to antifungal agents is becoming increasingly prevalent in Candida species (7). For example, C. lusitaniae, C. guilliermondii, and C. kefyr have been reported as resistant to amphotericin B (8).…”