Abstract
We tested a global collection of Candida sp. strains against anidulafungin, caspofungin, and micafungin, using CLSI M27-A3 broth microdilution (BMD) methods, in order to define wild-type (WT) populations and epidemiological cutoff values (ECVs). From 2003 to 2007, 8,271 isolates of Candida spp. (4,283 C. albicans, 1,236 C. glabrata, 1,238 C. parapsilosis, 996 C. tropicalis, 270 C. krusei, 99 C. lusitaniae, 88 C. guilliermondii, and 61 C. kefyr isolates) were obtained from over 100 centers worldwide. The modal MICs (in μg/ml) for anidulafungin, caspofungin, and micafungin, respectively, for each species were as follows: C. albicans, 0.03, 0.03, 0.015; C. glabrata, 0.06, 0.03, 0.015; C. tropicalis, 0.03, 0.03, 0.015; C. kefyr, 0.06, 0.015, 0.06; C. krusei, 0.03, 0.06, 0.06; C. lusitaniae, 0.05, 0.25, 0.12; C. parapsilosis, 2, 0.25, 1; and C. guilliermondii, 2, 0.5. 05. The ECVs, expressed in μg/ml (percentage of isolates that had MICs that were less than or equal to the ECV is shown in parentheses) for anidulafungin, caspofungin, and micafungin, respectively, were as follows: 0.12 (99.7%), 0.12 (99.8%), and 0.03 (97.7%) for C. albicans; 0.25 (99.4%), 0.12 (98.5%), and 0.03 (98.2%) for C. glabrata; 0.12 (98.9%), 0.12 (99.4%), and 0.12 (99.1%) for C. tropicalis; 0.25(100%), 0.03 (100%), and 0.12 (100%) for C. kefyr; 0.12 (99.3%), 0.25 (96.3%), and 0.12 (97.8%) for C. krusei; 2 (100%), 0.5 (98.0%), and 0.5 (99.0%) for C. lusitaniae; 4 (100%), 1 (98.6%), and 4 (100%) for C. parapsilosis; 16 (100%), 4 (95.5%), and 4 (98.9%) for C. guilliermondii. These WT MIC distributions and ECVs will be useful in surveillance for emerging reduced echinocandin susceptibility among Candida spp. and for determining the importance of various FKS1 or other mutations.
The members of the echinocandin class of antifungal agents (anidulafungin, caspofungin, and micafungin) are now well recognized as the preferred, systemically active antifungal agents for the treatment of invasive candidiasis (IC), including candidemia (19). The in vitro activity of these agents against Candida spp. is also well-known (17, 24), and the Clinical and Laboratory Standards Institute (CLSI) Antifungal Subcommittee has established a clinical breakpoint (CBP) for susceptibility of ≤2 μg/ml for all three agents and all species of Candida (3, 4, 25). Recently, however, it has become evident that Candida infections involving strains with mutations in FKS1 (encodes the echinocandin target) do not necessarily have MICs above this CBP (2, 5-8, 14, 28). Likewise, kinetic studies of the glucan synthesis enzyme complex suggest that a lower MIC cutoff of 0.5 μg/ml may be more sensitive in detecting those strains with FKS1 mutations (7, 8). Given these considerations, we have conducted global surveillance of Candida spp. by using CLSI broth microdilution (BMD) methods to ascertain the wild-type (WT) MIC distribution for the three echinocandins and the eight most common species of Candida causing bloodstream infections (BSI). This information allows us to establish epidemiological cutoff values (ECVs) that may be used to assess the emergence of strains with FKS1 mutations and the decreased susceptibility to these agents (10, 27, 30).
MATERIALS AND METHODS
Organisms.
A total of 8,271 clinical isolates obtained from more than 100 medical centers worldwide from 2003 through 2007 were tested. The collection included 4,283 strains of Candida albicans, 1,236 of Candida glabrata, 1,238 of Candida parapsilosis, 996 of Candida tropicalis, 270 of Candida krusei, 99 of Candida lusitaniae, 88 of Candida guilliermondii, and 61 of Candida kefyr. All isolates were obtained from blood or other normally sterile sites and represented the incident isolate from individual infectious episodes. The isolates were collected at individual study sites and were sent to the University of Iowa (Iowa City) for identification and susceptibility testing as described previously (20-23). The isolates were identified by standard methods (9) and stored as water suspensions until used in the study. Prior to testing, each isolate was passaged at least twice onto potato dextrose agar (Remel) and Chromagar Candida medium (Becton Dickinson and Company, Sparks, MD) to ensure purity and viability.
Antifungal agents.
Reference powders of anidulafungin, caspofungin, and micafungin were obtained from their respective manufacturers. Stock solutions were prepared in water (caspofungin and micafungin) or dimethyl sulfoxide (anidulafungin), and serial 2-fold dilutions in RPMI 1640 medium (Sigma, St. Louis, MO) buffered to pH 7.0 with 0.165 M MOPS (morpholinepropanesulfonic acid) buffer (Sigma) were made.
Antifungal susceptibility testing.
BMD testing was performed in accordance with the guidelines in CLSI document M27-A3 (3) by using RPMI 1640 medium, an inoculum of 0.5 × 103 to 2.5 × 103 cells/ml, and incubation at 35°C. MICs were determined visually, after 24 h of incubation, as the lowest concentration of drug that caused a significant diminution (≥50% inhibition) of growth below control levels (16, 20, 25).
Quality control.
Quality control was performed by testing CLSI-recommended strains C. krusei ATCC 6258 and C. parapsilosis ATCC 22019 (3, 4).
Definitions.
The definitions of WT and ECVs were those outlined previously (10, 26, 29, 30). A WT organism is defined as a strain which does not harbor any acquired resistance to the particular antimicrobial agent being examined (29, 30). The typical MIC distribution for WT organisms covers three to four 2-fold dilution steps surrounding the modal MIC (1, 11). Inclusion of WT strains in the present study was ensured by testing only the incident isolate for each infectious episode.
The ECV for each echinocandin and each species of Candida was obtained as described by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) (10), by considering the WT MIC distribution, the modal MIC for each distribution, and the inherent variability of the test (usually within 1 log2 dilution). In general, the ECV should encompass at least 95% of isolates in the WT distribution (29, 30). Statistical determination of ECVs for each species and antifungal agent was performed as described previously (29). Organisms with acquired resistance mechanisms may be included among those for which the MICs are higher than the ECV (1, 10, 11, 26).
The CBPs for susceptibility (MIC, ≤2 μg/ml) for all three echinocandins used in this study were those defined by Pfaller et al. (25) and CLSI (4).
RESULTS AND DISCUSSION
The WT MIC distributions for the three echinocandins and each of the eight species of Candida are shown in Table 1. These distributions clearly show the very low MICs typical of WT strains of C. albicans, C. glabrata, C. tropicalis, C. krusei, and C. kefyr and the higher MICs typical of C. parapsilosis, C. guilliermondii, and C. lusitaniae for all three echinocandins.
TABLE 1.
WT MIC distributions of anidulafungin, caspofungin and micafungin for eight species of Candida, using CLSI BMD methods
| Species | Antifungal agent | No. of isolates tested | No. of isolates with MIC (μg/ml) of: |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0.007 | 0.015 | 0.03 | 0.06 | 0.12 | 0.25 | 0.5 | 1 | 2 | 4 | >8 | |||
| C. albicans | Anidulafungin | 4,283 | 338 | 1,278 | 1,542 | 896 | 216 | 12 | 1 | ||||
| Caspofungin | 4,283 | 92 | 1,181 | 2,037 | 898 | 68 | 6 | 1 | |||||
| Micafungin | 4,283 | 608 | 2,952 | 625 | 90 | 5 | 1 | 1 | |||||
| C. glabrata | Anidulafungin | 1,236 | 7 | 161 | 715 | 320 | 26 | 2 | 2 | 2 | 1 | ||
| Caspofungin | 1,236 | 132 | 731 | 329 | 26 | 8 | 7 | 1 | 2 | ||||
| Micafungin | 1,236 | 208 | 935 | 71 | 12 | 4 | 2 | 1 | 2 | 1 | |||
| C. tropicalis | Anidulafungin | 996 | 41 | 254 | 493 | 173 | 24 | 7 | 1 | 3 | |||
| Caspofungin | 996 | 17 | 318 | 482 | 161 | 12 | 4 | 1 | 1 | ||||
| Micafungin | 996 | 46 | 400 | 375 | 149 | 17 | 6 | 1 | 2 | ||||
| C. krusei | Anidulafungin | 270 | 4 | 159 | 91 | 14 | 1 | 1 | |||||
| Caspofungin | 270 | 1 | 140 | 79 | 40 | 8 | 2 | ||||||
| Micafungin | 270 | 4 | 28 | 211 | 21 | 6 | |||||||
| C. kefyr | Anidulafungin | 61 | 1 | 6 | 31 | 23 | |||||||
| Caspofungin | 61 | 8 | 47 | 6 | |||||||||
| Micafungin | 61 | 4 | 27 | 30 | |||||||||
| C. lusitaniae | Anidulafungin | 99 | 5 | 14 | 33 | 43 | 4 | ||||||
| Caspofungin | 99 | 3 | 2 | 42 | 46 | 4 | 2 | ||||||
| Micafungin | 99 | 1 | 4 | 9 | 52 | 31 | 1 | 1 | |||||
| C. parapsilosis | Anidulafungin | 1,238 | 1 | 2 | 1 | 1 | 14 | 49 | 319 | 765 | 86 | ||
| Caspofungin | 1,238 | 2 | 5 | 31 | 126 | 545 | 399 | 113 | 16 | 1 | |||
| Micafungin | 1,238 | 2 | 2 | 1 | 10 | 66 | 261 | 676 | 220 | ||||
| C. guilliermondii | Anidulafungin | 88 | 1 | 5 | 7 | 5 | 31 | 32 | 7 | ||||
| Caspofungin | 88 | 1 | 10 | 7 | 21 | 32 | 12 | 1 | 4 | ||||
| Micafungin | 88 | 2 | 5 | 8 | 16 | 31 | 23 | 2 | 1 | ||||
The modal MICs (percentage of isolates with MICs equal to the mode is shown in parentheses) for anidulafungin, caspofungin, and micafungin, respectively, and each species are as follows (Table 2): C. albicans, 0.03 μg/ml (36.0%), 0.03 μg/ml (47.6%), 0.015 μg/ml (68.9%); C. glabrata, 0.06 μg/ml (57.8%), 0.03 μg/ml (59.1%), 0.015 μg/ml (75.6%); C. tropicalis, 0.03 μg/ml (49.5%), 0.03 μg/ml (48.4%), 0.015 μg/ml (40.2%); C. krusei, 0.03 μg/ml (58.9%), 0.06 μg/ml (51.9%), 0.06 μg/ml (78.1%); C. kefyr, 0.06 μg/ml (50.8%), 0.015 μg/ml (77.0%), 0.06 μg/ml (49.2%); C. lusitaniae, 0.5 μg/ml (43.4%), 0.25 μg/ml (46.5%), 0.12 μg/ml (52.5%); C. parapsilosis, 2 μg/ml (61.8%), 0.25 μg/ml (44.0%), 1 (54.6%); C. guilliermondii, 2 μg/ml (36.4%), 0.5 μg/ml (36.4%), 0.5 μg/ml (35.2%).
TABLE 2.
ECVs for anidulafungin, caspofungin, and micafungin and eight species of Candida
| Species | Antifungal agent | No. of isolates tested | MIC (μg/ml) |
% Isolates with MIC of ≤2 μg/ml | ||
|---|---|---|---|---|---|---|
| Range | Mode | ECV (%a) | ||||
| C. albicans | Anidulafungin | 4,283 | 0.007-1 | 0.03 | 0.12 (99.7) | 100.0 |
| Caspofungin | 4,283 | 0.007-0.5 | 0.03 | 0.12 (99.8) | 100.0 | |
| Micafungin | 4,283 | 0.007-0.5 | 0.015 | 0.03 (97.7) | 100.0 | |
| C. glabrata | Anidulafungin | 1,236 | 0.015-4 | 0.06 | 0.25 (99.4) | 99.9 |
| Caspofungin | 1,236 | 0.015-8 | 0.03 | 0.12 (98.5) | 99.8 | |
| Micafungin | 1,236 | 0.007-2 | 0.015 | 0.03 (98.2) | 100.0 | |
| C. tropicalis | Anidulafungin | 996 | 0.007-2 | 0.03 | 0.12 (98.9) | 100.0 |
| Caspofungin | 996 | 0.007->8 | 0.03 | 0.12 (99.4) | 99.9 | |
| Micafungin | 996 | 0.007-1 | 0.015 | 0.12 (99.1) | 100.0 | |
| C. kefyr | Anidulafungin | 61 | 0.015-0.12 | 0.06 | 0.25 (100.0) | 100.0 |
| Caspofungin | 61 | 0.007-0.03 | 0.015 | 0.03 (100.0) | 100.0 | |
| Micafungin | 61 | 0.015-0.06 | 0.06 | 0.12 (100.0) | 100.0 | |
| C. krusei | Anidulafungin | 270 | 0.015-0.5 | 0.03 | 0.12 (99.3) | 100.0 |
| Caspofungin | 270 | 0.015-1 | 0.06 | 0.25 (96.3) | 100.0 | |
| Micafungin | 270 | 0.015-0.25 | 0.06 | 0.12 (97.8) | 100.0 | |
| C. lusitaniae | Anidulafungin | 99 | 0.06-1 | 0.5 | 2 (100) | 100.0 |
| Caspofungin | 99 | 0.03-1 | 0.25 | 0.5 (98.0) | 100.0 | |
| Micafungin | 99 | 0.007-1 | 0.12 | 0.5 (99.0) | 100.0 | |
| C. parapsilosis | Anidulafungin | 1,238 | 0.015-4 | 2 | 4 (100.0) | 93.1 |
| Caspofungin | 1,238 | 0.015-4 | 0.25 | 1 (98.6) | 99.9 | |
| Micafungin | 1,238 | 0.015-2 | 1 | 4 (100) | 100.0 | |
| C. guilliermondii | Anidulafungin | 88 | 0.06-4 | 2 | 16 (100.0) | 92.0 |
| Caspofungin | 88 | 0.03->8 | 0.5 | 4 (95.5) | 95.5 | |
| Micafungin | 88 | 0.015->8 | 0.5 | 4 (98.9) | 98.9 | |
Percentage of isolates for which MIC is less than or equal to the ECV.
The ECVs (percentage of isolates with MICs that were less than or equal to the ECVs is shown in parentheses) were calculated as described by Turnidge et al. (29), taking into consideration the WT MIC distributions and the inherent variability of the BMD test method, and were as follows for each species and anidulafungin, caspofungin, and micafungin, respectively (Table 2): 0.12 μg/ml (99.7%), 0.12 μg/ml (99.8%), and 0.03 μg/ml (97.7%) for C. albicans; 0.25 μg/ml (99.4%), 0.12 μg/ml (98.5%), and 0.03 μg/ml (98.2%) for C. glabrata; 0.12 μg/ml (98.9%), 0.12 μg/ml (99.4%), and 0.12 μg/ml (99.1%) for C. tropicalis; 0.25 μg/ml (100%), 0.03 μg/ml (100%), and 0.12 μg/ml (100%) for C. kefyr; 0.12 μg/ml (99.3%), 0.25 μg/ml (96.3%), and 0.12 μg/ml (97.8%) for C. krusei; 2 μg/ml (100%), 0.5 μg/ml (98.0%), and 0.5 μg/ml (99.0%) for C. lusitaniae; 4 μg/ml (100%), 1 μg/ml (98.6%), and 4 μg/ml (100%) for C. parapsilosis; and 16 μg/ml (100%), 4 μg/ml (95.5%), and 4 μg/ml (98.9%) for C. guilliermondii.
Compared to the CBP value of ≤2 μg/ml, the ECVs are between 8- and 66-fold lower for the three echinocandins and C. albicans, C. glabrata, C. tropicalis, C. krusei, and C. kefyr (Table 2). Whereas the CBP encompasses 99.9% to 100% of the isolates of these five species, the ECVs of each agent encompass 96% to 100% of the isolates, highlighting the small number of isolates of each species that fall outside of the WT distribution yet remain susceptible to each agent according to the CBP. In contrast, the ECVs for the three less susceptible species, C. lusitaniae, C. parapsilosis, and C. guilliermondii, are similar to the CBPs for all three of the echinocandins.
Generally speaking, CBPs are used to indicate those isolates that are likely to respond to treatment with a given antimicrobial agent administered at the approved dosing regimen for that agent, whereas the ECV can be used as the most sensitive measure of the emergence of strains with reduced susceptibility to a given agent (10, 11, 27). Although organisms whose MICs exceed the ECV show reduced susceptibility compared with the WT population and may exhibit one or more acquired resistance mechanisms, they may yet respond to clinical treatment, as their MIC may lie below the CBP (27).
Although the various clinical trials have shown that each of the three echinocandins can be used to treat candidemia and IC due to isolates of Candida spp. for which MICs are as high as 2 μg/ml (12, 13, 15, 18, 25), several recent reports of clinical resistance to caspofungin therapy (Table 3), as well as studies of glucan synthase (GS) enzyme kinetics (6-8), suggest that the CBP of ≤2 μg/ml may need to be adjusted to predict both clinical resistance as well as the emergence of strains with FKS1 mutations. In each of the cases shown in Table 3, clinical failure of caspofungin therapy was associated with FKS1 mutations and MICs for all three echinocandins that were elevated compared to the WT but not necessarily higher than the CBP of ≤2 μg/ml. Application of the ECVs in Table 2 would have recognized these strains as non-WT and thus likely to contain an acquired resistance mutation.
TABLE 3.
Clinical and in vitro resistance: caspofungin in candidiasis patientsb
| Species (reference) | Infection type | Antifungal treatmenta | Agents (MICs in μg/ml) | Comment(s) |
|---|---|---|---|---|
| C. glabrata (28) | Candidemia | CSF | CSF (2), ANF (0.5), MCF (0.25) | Mutation in FKS2, F659V |
| C. albicans (2) | Esophagitis | FLC, VRC, CSF, AMB | CSF (2), MCF (1) | Mutation in FKS1, F641S |
| C. tropicalis (6) | Candidemia | CSF, VRC | CSF (4), ANF (2), MCF (2) | Mutation, 50× increase in IC50 |
| C. tropicalis (6) | Candidemia | CSF, AMB | CSF (4), ANF (1), MCF (2) | Mutation, 50× increase in IC50 |
| C. tropicalis (6) | Candidemia | CSF, FLC | CSF (1), ANF (0.5), MCF (0.5) | Mutation, 38× increase in IC50 |
| C. albicans (14) | Esophagitis | CSF, AMB, FLC, VRC, ITZ, MCF | CSF (2), ANF (1), MCF (2) | Mutations, S645F and R1361H |
Antifungal agents administered to patient.
AMB, amphotericin B; ANF, anidulafungin; CSF, caspofungin; FLC, fluconazole; ITZ, itraconazole; MCF, micafungin; VRC, voriconazole; IC50, concentration that inhibits 50% of enzyme activity.
It is evident that only a small number (<4%) of isolates of C. albicans, C. glabrata, C. tropicalis, and C. krusei fall outside of the respective ECVs for each of the three echinocandins (Tables 1 and 2). Almost all would be classified as susceptible using the CBP criteria despite the possibility that they may have an acquired FKS1 mutation. The questions that must be answered are (i) what proportion of these isolates do in fact contain a target enzyme mutation and (ii) is the presence of a mutation that does not result in an MIC that is greater than the CBP meaningful or necessary to detect?
Garcia-Effron et al. (7, 8) demonstrated that clinically resistant isolates of C. albicans and C. glabrata with mutations in FKS1 and/or FKS2 showed elevated MICs and altered GS enzyme kinetics for all three echinocandins. Importantly, an MIC of >0.5 μg/ml identified those strains with resistant GS for anidulafungin, caspofungin, and micafungin.
Likewise, Wiederhold et al. (31) examined 12 strains of C. albicans for which the MICs of anidulafungin (MIC range, 0.12 to 1 μg/ml), caspofungin (MIC range, 2 to 8 μg/ml), and micafungin (MIC range, 0.5 to 4 μg/ml) were elevated relative to the control (WT) MIC for each agent (0.03 μg/ml, 0.125 μg/ml, and 0.06 μg/ml, respectively). All 12 isolates were found to contain mutations in FKS1; however, the MICs exceeded the CBPs for 0 of 12 strains with anidulafungin, 9 of 12 with caspofungin, and 2 of 12 with micafungin. In contrast, all 12 would have been considered to have reduced susceptibility to caspofungin and micafungin, and nine would have been considered to have reduced susceptibility to anidulafungin, using the ECVs shown in Table 2. Unfortunately, no clinical data concerning these strains were presented by the authors.
Thus, the ECVs determined for C. albicans, C. glabrata, C. tropicalis, C. krusei, and C. kefyr will be important in detecting the emergence of decreased susceptibility to the echinocandins in ongoing surveillance efforts. The CBPs for these agents may serve the same purpose for C. parapsilosis and C. guilliermondii but appear to be too insensitive to be of epidemiological value in monitoring the more susceptible species. Future studies must include molecular analysis of FKS1 and FKS2 for the mutant strains with values that fall between the ECV and CBP to better understand the frequency and clinical importance of such mutations. The establishment of the WT MIC distributions and ECVs for each echinocandin and species of Candida will be useful in resistance surveillance and may prove to be an important step in the development of species-specific CBPs for this important class of antifungal agents.
Acknowledgments
Caitlin Howard provided excellent support in the preparation of the manuscript. The input of Gunnar Kahlmeter is gratefully acknowledged.
This work was supported in part by grants from Astellas and Pfizer.
Footnotes
Published ahead of print on 18 November 2009.
REFERENCES
- 1.Arendrup, M. C., G. Kahlmeter, J. L. Rodriguez-Tudela, and J. P. Donnelly. 2009. Breakpoints for susceptibility testing should not divide wild-type distributions of important target species. Antimicrob. Agents Chemother. 53:1628-1629. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Baixench, M. T., N. Aoun, M. Desnos-Ollivier, D. Garcia-Hermosa, S. Bretagne, S. Ramires, C. Piketty, and E. Dannaoui. 2007. Acquired resistance to echinocandins in Candida albicans: case report and review. J. Antimicrob. Chemother. 59:1076-1083. [DOI] [PubMed] [Google Scholar]
- 3.Clinical and Laboratory Standards Institute. 2008. Reference method for broth dilution antifungal susceptibility testing of yeasts, 3rd ed. Approved standard M27-A3. Clinical and Laboratory Standards Institute, Wayne, PA.
- 4.Clinical and Laboratory Standards Institute. 2008. Reference method for broth dilution antifungal susceptibility testing of yeasts. Informational supplement M27-S3. Clinical and Laboratory Standards Institute, Wayne, PA.
- 5.Desnos-Ollivier, M., S. Bretagne, D. Raoux, D. Hoinard, F. Dromer, and E. Dannaoui. 2008. Mutations in the fks1 gene in Candida albicans, C. tropicalis, and C. krusei correlate with elevated caspofungin MICs uncovered in AM3 medium using the method of the European Committee on Antibiotic Susceptibility Testing. Antimicrob. Agents Chemother. 52:3092-3098. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Garcia-Effron, G., D. P. Kontoyiannis, R. E. Lewis, and D. S. Perlin. 2008. Caspofungin-resistant Candida tropicalis strains causing breakthrough fungemia in patients at high risk for hematologic malignancies. Antimicrob. Agents Chemother. 52:4181-4183. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Garcia-Effron, G., S. Park, and D. S. Perlin. 2009. Correlating echinocandin MIC and kinetic inhibition of fks1 mutant glucan synthases for Candida albicans: implications for interpretive breakpoints. Antimicrob. Agents Chemother. 53:112-122. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8.Garcia-Effron, G., S. Lee, S. Park, J. D. Cleary, and D. S. Perlin. 2009. Effect of Candida glabrata FKS1 and FKS2 mutations on echinocandin sensitivity and kinetics of 1,3-β-d-glucan synthase: implication for the existing susceptibility breakpoint. Antimicrob. Agents Chemother. 53:3690-3699. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Hazen, K. C., and S. A. Howell. 2007. Candida, Cryptococcus, and other yeasts of medical importance, p. 1762-1788. In P. R. Murray, E. J. Baron, J. H. Jorgensen, M. L. Landry, and M. A. Pfaller (ed.), Manual of clinical microbiology, 9th ed. ASM Press, Washington, DC.
- 10.Kahlmeter, G., D. F. J. Brown, F. W. Goldstein, A. P. McGowan, J. W. Mouton, A. Osterlund, A. Rodloff, M. Steinbakk, P. Urbaskova, and A. Vatopoulos. 2003. European harmonization of MIC breakpoints for antimicrobial susceptibility testing of bacteria. J. Antimicrob. Chemother. 52:145-148. [DOI] [PubMed] [Google Scholar]
- 11.Kahlmeter, G., and D. F. J. Brown. 2004. Harmonization of antimicrobial breakpoints in Europe—can it be achieved? Clin. Microbiol. Newsl. 26:187-192. [Google Scholar]
- 12.Kartsonis, M. N., J. Killar, L. Mixson, C. M. Hoe, C. Sable, K. Bartizal, and M. Motyl. 2005. Caspofungin susceptibility testing of isolates from patients with esophageal candidiasis or invasive candidiasis: relationship of MIC to treatment outcome. Antimicrob. Agents Chemother. 49:3616-3623. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Kuse, E. R., P. Chutchotisadk, C. A. da Cunha, M. Ruhnke, C. Barrios, D. Raghunadharao, J. S. Sekhon, A. Freire, V. Ramasubramanian, I. Demeyer, M. Nucci, A. Leelarasamee, F. Jacobs, J. Decruyenaere, D. Pittet, A. J. Ullman, L. Ostrosky-Zeichner, O. Lortholary, S. Kobling, H. Diekmann-Berndt, O. A. Cornely, and the Micafungin Invasive Candidiasis Working Group. 2007. Micafungin versus liposomal amphotericin B for candidaemia and invasive candidosis: a phase III randomized double-blind trial. Lancet 369:1519-1527. [DOI] [PubMed] [Google Scholar]
- 14.Laverdière, M., R. G. Lalonde, J. G. Baril, D. C. Sheppard, S. Park, and D. S. Perlin. 2006. Progressive loss of echinocandin activity following prolonged use for treatment of Candida albicans oesophagitis. J. Antimicrob. Chemother. 57:705-708. [DOI] [PubMed] [Google Scholar]
- 15.Mora-Duarte, J., R. Betts, C. Rotstein, A. L. Colombo, L. Thompson-Moya, J. Smietana, R. Lupinacci, C. Sable, N. Kartsonis, and J. Perfect. 2002. Comparison of caspofungin and amphotericin B for invasive candidiasis. N. Engl. J. Med. 347:2020-2029. [DOI] [PubMed] [Google Scholar]
- 16.Odds, F. C., M. Motyl, R. Androde, J. Bille, E. Canton, M. Cuenca-Estrella, A. Davidson, C. Durussell, D. Ellis, E. Foraker, A. W. Fothergill, M. A. Ghannoum, R. A. Giacobbe, M. Governado, R. Handkie, M. Laverdiere, W. Lee-Yang, W. G. Merz, L. Ostrosky-Zeichner, J. Peman, S. Perea, J. R. Perfect, M. A. Pfaller, L. Proia, J. H. Rex, M. G. Rinaldi, J. L. Rodriguez-Tudela, W. A. Schell, C. Sheilds, D. A. Sutton, P. E. Verweij, and D. W. Warnock. 2004. Interlaboratory comparison of results of susceptibility testing with caspofungin against Candida and Aspergillus species. J. Clin. Microbiol. 42:3475-3482. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 17.Ostrosky-Zeichner, L., J. H. Rex, P. G. Pappas, R. J. Hamill, R. A. Larsen, H. W. Horowitz, W. G. Powderly, N. Hyslop, C. A. Kauffman, J. Cleary, J. E. Mangeno, and J. Lee. 2003. Antifungal susceptibility survey of 2,000 bloodstream Candida isolates in the United States. Antimicrob. Agents Chemother. 47:3149-3154. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 18.Pappas, P. G., C. M. Rotstein, R. F. Betts, M. Nucci, D. Talwar, J. J. De Waele, J. A. Vasquez, B. F. Dupont, D. L. Horn, L. Ostrosky-Zeichner, A. C. Reboli, B. Suh, R. Digumarti, C. Wu, L. L. Kovanda, L. J. Arnold, and D. N. Buell. 2007. Micafungin versus caspofungin for treatment of candidemia and other forms of invasive candidiasis. Clin. Infect. Dis. 45:883-893. [DOI] [PubMed] [Google Scholar]
- 19.Pappas, P. G., C. A. Kauffman, D. Andes, D. K. Benjamin, T. F. Calandra, J. E. Edwards, S. G. Filler, J. F. Fisher, B. J. Kulhberg, L. Ostrosky-Zeichner, A. C. Reboli, J. H. Rex, T. J. Walsh, and J. D. Sobel. 2009. Clinical practice guidelines for the management of candidiasis: 2009 update by the Infectious Diseases Society of America. Clin. Infect. Dis. 48:503-535. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 20.Pfaller, M. A., S. A. Messer, L. Boyken, C. Rice, S. Tendolkar, R. J. Hollis, and D. J. Diekema. 2004. Further standardization of broth microdilution methodology for in vitro susceptibility testing of caspofungin against Candida species by use of an international collection of more than 3,000 clinical isolates. J. Clin. Microbiol. 42:3117-3119. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 21.Pfaller, M. A., L. Boyken, R. J. Hollis, S. A. Messer, S. Tendolkar, and D. J. Diekema. 2005. In vitro activities of anidulafungin against more than 2,500 clinical isolates of Candida spp., including 315 isolates resistant to fluconazole. J. Clin. Microbiol. 43:5425-5427. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 22.Pfaller, M. A., L. Boyken, R. J. Hollis, S. A. Messer, S. Tendolkar, and D. J. Diekema. 2006. In vitro susceptibilities of Candida spp. to caspofungin: four years of global surveillance. J. Clin. Microbiol. 44:760-763. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 23.Pfaller, M. A., L. Boyken, R. J. Hollis, S. A. Messer, S. Tendolkar, and D. J. Diekema. 2006. Global surveillance of in vitro activity of micafungin against Candida: a comparison with caspofungin by CLSI-recommended methods. J. Clin. Microbiol. 44:3533-3538. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 24.Pfaller, M. A., L. Boyken, R. J. Hollis, J. Kroeger, S. A. Messer, S. Tendolkar, and D. J. Diekema. 2008. In vitro susceptibility of invasive isolates of Candida spp. to anidulafungin, caspofungin, and micafungin: six years of global surveillance. J. Clin. Microbiol. 46:15-156. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 25.Pfaller, M. A., D. J. Diekema, L. Ostrosky-Zeichner, J. H. Rex, B. D. Alexander, D. Andes, S. D. Brown, V. Chaturvedi, M. A. Ghannoum, C. C. Knapp, D. J. Sheehan, and T. J. Walsh. 2008. Correlation of MIC with outcome for Candida species tested against caspofungin, anidulafungin, and micafungin: analysis and proposal for interpretive MIC breakpoints. J. Clin. Microbiol. 46:2620-2629. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 26.Rodriguez Tudela, J. L., J. P. Donnelly, M. C. Arendrup, S. Arikan, F. Barchiesi, J. Bille, E. Chryssanthou, M. Cuenca-Estrella, E. Dannaoui, D. Denning, W. Fegeler, P. Gaustad, N. Klimko, C. Lass-Florl, C. Moore, M. Richardson, A. Schmalreck, J. Stenderup, A. Velegraki, and P. Verweij. 2008. EUCAST technical note on fluconazole. Clin. Microbiol. Infect. 14:193-195. [DOI] [PubMed] [Google Scholar]
- 27.Simjee, S., P. Silley, H. O. Werling, and R. Bywater. 2008. Potential confusion regarding the term “resistance” in epidemiological surveys. J. Antimicrob. Chemother. 61:228-229. [DOI] [PubMed] [Google Scholar]
- 28.Thompson, G. R., III, N. P. Wiederhold, A. C. Vallor, N. C. Villareal, J. S. Lewis, and T. F. Patterson. 2008. Development of caspofungin resistance following prolonged therapy for invasive candidiasis secondary to Candida glabrata infection. Antimicrob. Agents Chemother. 52:3783-3785. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 29.Turnidge, J., G. Kahlmeter, and G. Kronvall. 2006. Statistical characterization of bacterial wild-type MIC value distributions and determination of epidemiological cut-off values. Clin. Microbiol. Infect. 12:418-425. [DOI] [PubMed] [Google Scholar]
- 30.Turnidge, J., and D. L. Paterson. 2007. Setting and revising antibacterial susceptibility breakpoints. Clin. Microbiol. Rev. 20:391-408. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 31.Wiederhold, N. P., J. L. Grabinski, G. Garcia-Effron, D. S. Perlin, and S. A. Lee. 2008. Pyrosequencing to detect mutations in FKS1 that confer reduced echinocandin susceptibility in Candida albicans. Antimicrob. Agents Chemother. 52:4145-4148. [DOI] [PMC free article] [PubMed] [Google Scholar]