In Vitro Activities of Echinocandins againstCandida kruseiDetermined by Three Methods: MIC and Minimal Fungicidal Concentration Measurements and Time-Kill Studies

Abstract

We evaluated the in vitro activities of anidulafungin, micafungin, and caspofungin against Candida krusei by determining MIC and minimum fungicidal concentration (MFC) measurements and by the time-kill method. The geometric mean (GM)-MIC/GM-MFC values were 0.1/0.34, 0.25/0.44, and 1/2.29, respectively. The mean times to reach 99.9% growth reduction were 19.1 ؎ 18.2 h (mean ؎ standard deviation) for 2 mg/liter anidulafungin, 37.4 ؎ 8.8 h for 2 mg/liter caspofungin, and 30.7 ؎ 12.2 h for 1 mg/liter micafungin. Anidulafungin exhibited the highest time-kill rate, followed by micafungin. The three echinocandins showed fungicidal activity at concentrations reached in serum.Candida krusei is isolated mainly from immunocompromised patients and those who have received fluconazole treatment. The isolation (2 to 60%) and mortality (30 to 60%) rates depend on the institution and on the unit to which the patient is admitted (10,13,14,17,20). Treatment of invasive C. krusei infections can be difficult due to its intrinsic resistance to fluconazole and its reduced susceptibility to amphotericin B and flucytosine (2, 15). In immunocompromised patients, fungicidal agents may be required to eradicate infection since the major host defense (phagocytic killing of neutrophils and monocytes/macrophages) is reduced (9).Anidulafungin, caspofungin, and micafungin are novel antifungals that share the same spectrum of activity but differ in their MICs. Although the fungicidal activities and killing rates of echinocandins have been previously evaluated (3,7,8,16), none of these studies performed a head-to-head comparison. However, these agents also may differ in their fungicidal activities. This study aimed to determine their relative antifungal activities against C. krusei by three measures: (i) MICs, (ii) minimal fungicidal concentrations (MFCs), and (iii) time-kill curves.Anidulafungin (Pfizer España, Madrid, Spain), caspofungin (Merck Sharpe & Dome, Madrid, Spain), and micafungin (Fugisawa Pharmaceutical Company, Japan) were provided by their manufacturers. Caspofungin and micafungin were dissolved in water and anidulafungin in dimethyl sulfoxide; further dilutions were prepared in standard RPMI 1640 medium (Sigma-Aldrich, Madrid, Spain). Final anidulafungin and micafungin drug concentrations ranged from 0.03 to 16 mg/liter, and that of caspofungin from 0.12 to 64 mg/liter. MIC and MFC values were obtained for 20 C. krusei bloodstream isolates, the caspofungin-resistant strain CY-118 (MIC Ͼ 8 mg/liter) (11), and C. krusei ATCC 6258. MICs were determined by following the CLSI M27-A3 microdilution

Comparison of Anidulafungin MICs Determined by the Clinical and Laboratory Standards Institute Broth Microdilution Method (M27-A3 Document) and Etest for Candida Species Isolates

“…has been associated with high MICs, mutations in the FKS1 gene, and therapeutic failure (2,4,8,13,14,20,25). MICs higher than those for other species are consistently observed for C. parapsilosis and C. guilliermondii (28), along with reduced glucan synthase sensitivity (19) and a lack of killing activity for C. guilliermondii (5,6,7).…”

“…The 143 isolates included caspofungin-resistant (six heterozygous and homozygous C. albicans mutants, one C. krusei isolate), caspofungin-susceptible (Table 1), and quality control (QC; C. parapsilosis ATCC 22019 and C. krusei ATCC 6258) isolates (8,15,23); anidulafungin MICs were within the established QC limits (12).…”

Amino Acid-Derived 1,2-Benzisothiazolinone Derivatives as Novel Small-Molecule Antifungal Inhibitors: Identification of Potential Genetic Targets

“…Although the BZT compounds were active against a panel of fungal pathogens described above, we next screened the BZT compounds against a variety of clinical or laboratory-constructed antifungal drug-resistant strains of C. albicans and C. glabrata and, when possible, their parental strains. Strains were selected to represent some of the mechanisms that are commonly found in clinically resistant isolates (10,16,17,19,22,34,38,39,46,56,59) (Tables 4 and 5). The MIC 50 values of all BZT compounds remained unchanged against C. albicans strains resistant to fluconazole.…”

Dose escalation studies with caspofungin against Candida glabrata

“…The fungicidal activity of caspofungin was defined as a 99.9% or higher reduction in viable cell count compared with the starting inoculum (Cantó n et al, 2009(Cantó n et al, , 2010Gil-Alonso et al, 2015). Killing kinetics at the tested concentrations were analysed in both media (RPMI and RPMI 1640 plus 50% serum), as described previously (Cantó n et al, 2009(Cantó n et al, , 2010Földi et al, 2012a, b;Gil-Alonso et al, 2015;Kovács et al, 2014a, b). An exponential equation was fitted to the mean data at each time point: N t 5N 0 |e 2kt , where N t is the number of viable yeasts at time t, N 0 is the number of viable yeasts in the initial inoculum, k is the killing rate and t is the incubation time.…”

“…The goodness of fit for each isolate was assessed by the r 2 value (r 2 w0.8). The mean times to achieve the fungicidal end point (T 99.9 53/k) were calculated from the k values for each isolate and concentrations in both media as described previously (Cantó n et al, 2009(Cantó n et al, , 2010Gil-Alonso et al, 2015;Kovács et al, 2014a, b). For control strains, the time to achieve a 1 log increase in c.f.u.…”