JCM Accepts, published online ahead of print on 8 January 2014 J. Clin. Microbiol. doi:10.1128/JCM.03044-13 Copyright © 2014, American Society for Microbiology. All Rights Reserved.
1
The Impact of New Antifungal Breakpoints on Antifungal Resistance in Candida
2
Species
3
Annette W. Fothergill, Deanna A. Sutton, Dora I. McCarthy, Nathan P. Wiederhold
4
Fungus Testing Laboratory, Department of Pathology, University of Texas Health
5
Science Center at San Antonio, San Antonio, TX
6 7
Abstract Word Count: 74
8
Keywords: antifungal breakpoints, Candida species, resistance
Manuscript Word Count: 1237
9 10
Corresponding Author:
11
Nathan P. Wiederhold, Pharm.D.
12
Associate Professor
13
UTHSCSA
14
Department of Pathology, MC 7750
15
7703 Floyd Curl Drive
16
San Antonio, TX 78229
17
Phone: 210-567-4086
18
Email: [email protected]
19 20 21 22 23
1
24
ABSTRACT
25
We reviewed our antifungal susceptibility data for micafungin, anidulafungin,
26
fluconazole, and voriconazole against Candida species, and compared resistance rates as
27
determined by the previous and recently revised CLSI antifungal breakpoints. With the
28
new breakpoints, resistance was significantly increased for micafungin (from 0.8% to
29
7.6%), anidulafungin (0.9% to 7.3%) and voriconazole (6.1% to 18.4%) against C.
30
glabrata. Resistance was also increased for fluconazole against C. albicans (2.1% to
31
5.7%).
32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
2
47
The Clinical and Laboratory Standards Institute (CLSI) recently revised the azole
48
and echinocandin clinical breakpoints against Candida species (1). These new
49
breakpoints are now both drug and species specific, whereas the previous breakpoints
50
were not. For most species, with the exception of C. parapsilosis and C. guilliermondii
51
against the echinocandins, the breakpoints have been lowered, such that previously
52
susceptible minimum inhibitory concentrations (MIC) are now classified as resistant. In
53
addition, C. glabrata isolates are no longer considered susceptible to fluconazole, but are
54
rather classified only as either susceptible dose-dependent or resistant. The breakpoint
55
revisions were made based on information from clinical studies, case reports describing
56
clinical failure at MIC values below the previous breakpoints, results from
57
pharmacokinetic/pharmacodynamics studies, and epidemiologic cut-off values (2, 3).
58
Additionally, a goal of harmonizing the antifungal breakpoints with those set by
59
EUCAST was sought. Epidemiologic cut-off values for individual species are used to
60
optimize the detection of non-wild type strains and thus the acquisition of resistance
61
mechanisms, and to prevent the breakpoints from dividing wild-type populations (2-4).
62
The impact of the revised clinical breakpoints regarding categorical placement of
63
Candida strains as resistant is unknown. Our objective was to evaluate what effect the
64
new antifungal clinical breakpoints may have on azole and echinocandin resistance
65
patterns in Candida species.
66
The antifungal susceptibility database in the Fungus Testing Laboratory at the UT
67
Health Science Center at San Antonio was reviewed. Susceptibility data for fluconazole,
68
voriconazole, anidulafungin, and micafungin against C. albicans, C. glabrata, C.
69
tropicalis, C. krusei, and C. parapsilosis isolates sent to our laboratory for testing
3
70
between January 1, 2008 and December 31, 2012 were reviewed. During this period,
71
antifungal powders were obtained from the appropriate manufacturers (Pfizer and
72
Astellas), and stock solutions were prepared in water for agents with aqueous solubility,
73
or in DMSO as recommended (1, 5). Susceptibility testing was performed by broth
74
microdilution methodology in RPMI according to the CLSI M27-A3 guidelines (5), and a
75
50% inhibition of growth compared to the growth control well was used as the endpoint
76
for all agents. Candida krusei ATCC 6258 and C. parapsilosis ATCC 22019 served as
77
the quality control isolates for each testing run, and the results were consistently within
78
the range specified by the CLSI. Isolates were classified as resistant based on both the
79
previous and recently revised CLSI clinical breakpoints (Table 1) (1). For voriconazole
80
against C. glabrata the epidemiologic cut-off value of 0.5 μg/mL was used for the new
81
threshold for resistance, as the CLSI has not set clinical breakpoints for this triazole
82
against this species (1, 6, 7). Thus, C. glabrata isolates with a voriconazole MIC above
83
this value (i.e., > 1 μg/mL) were classified as resistant. Differences in resistance rates
84
between the previous and revised breakpoints were assessed for significance by Fischer’s
85
exact test, and a p-value of < 0.05 was considered to be significant.
86
The number of each Candida species tested with each drug, the MIC range,
87
MIC50 and MIC90 values, and the percent of isolates classified as resistant per the
88
previous and revised breakpoints are shown in Table 2, and the MIC distributions are
89
shown in Table 3. As shown in this table and in Figure 1, resistance did increase with the
90
new breakpoints. For the echinocandins anidulafungin and micafungin, the most marked
91
changes occurred against C. glabrata. For this species, the number of isolates classified
92
as resistant increased from 1 (0.9%) to 8 (7.3%) of 110 isolates (p = 0.0353) for
4
93
anidulafungin and from 3 (0.8%) to 27 (7.6%) of 354 isolates (p < 0.0001) for
94
micafungin when the new CLSI clinical breakpoints were applied. Our rates of
95
micafungin and anidulafungin resistance with the new CLSI clinical breakpoints are
96
higher than those recently reported in the SENTRY study (1.3% and 1.6%, respectively)
97
(6). However, others have found higher rates of echinocandin resistance for this species,
98
with rates of micafungin and anidulafungin resistance reported to range from 9% to 12%
99
between 2007 and 2010 at a large medical center in the U.S. (8). Against the other
100
Candida species, the number of isolates considered to be resistant remained relatively
101
low, and for anidulafungin against C. parapsilosis, the number actually decreased slightly
102
from 2 to 0 isolates (2.4% to 0%), although this reduction was not statistically significant.
103
This was not unexpected against this species, as the CLSI echinocandin breakpoints
104
against C. parapsilosis were raised from > 4 μg/mL as non-susceptible to > 8 μg/mL as
105
resistant.
106
The azoles fluconazole and voriconazole were also affected by the revised
107
breakpoints. Against C. albicans, the number of isolates classified as resistant to
108
fluconazole by the new breakpoints significantly increased from 25 (2.1%) to 68 (5.7%)
109
of a total of 1196 strains tested (p < 0.0001; Table 2 and Figure 1) compared to the
110
previous threshold for resistance. This rate of fluconazole resistance in C. albicans is
111
higher than what was recently reported in isolates from North American institutions in
112
the SENTRY study (0.6%) (6). There were also trends for increased resistance to
113
fluconazole with the new breakpoints against C. tropicalis (19 to 32 of 327 isolates [6%
114
to 9.9%]; p = 0.0557) and C. parapsilosis (3 to 11 of 497 isolates [0.6% to 2.2%]; p =
115
0.0793). A similar observation was also found for voriconazole against C. albicans (17
5
116
to 27 of 593 isolates [2.9% to 4.6%]; p = 0.17), although this difference was not
117
significant. In contrast, only minor increases in voriconazole resistance against C.
118
tropicalis (30 to 36 of 205 isolates [14.6% to 17.6%]), and C. krusei (4 to 7 of 98 isolates
119
[4.1% to 12.2%]) were observed when the new breakpoints were applied. A significant
120
increase in the number of C. glabrata isolates that were classified as resistant to
121
voriconazole (32 to 96 of 522 isolates [6.1% to 18.4%]; p < 0.0001) was observed when
122
the epidemiologic cut-off value was used. The revised CLSI breakpoints for the azoles
123
are supported by epidemiologic cut-off values and the results of various
124
pharmacodynamics analyses (9-12), as well as by the cross-resistance observed among
125
different members of this class in Candida species (13-16). For most species, our rates of
126
fluconazole and voriconazole resistance were higher than those reported in the SENTRY
127
study (6). This may be a reflection of the nature of our reference laboratory in that we
128
may often be sent isolates from patients exposed to antifungals who are failing therapy.
129
Thus, some of the isolates we receive for susceptibility testing may be more likely be
130
non-wild type strains. However, the overall MIC distributions from our study shown in
131
Table 3 are similar to those reported by others including those from large surveillance
132
studies (6, 7, 17).
133
The results from our laboratory demonstrate that the rates of resistance for the
134
echinocandins and the azoles may be increased with the use of the new CLSI antifungal
135
breakpoints. These changes were especially marked for micafungin, anidulafungin, and
136
voriconazole against C. glabrata and for fluconazole against C. albicans. One limitation
137
of this study is that we did not determine if the isolates harbored mechanisms of acquired
138
antifungal resistance. Although this information is important, it would not change how
6
139
an isolate is classified as susceptible or resistant by the CLSI breakpoints, which is
140
determined by the phenotypic MIC. The clinical relevance of our findings is unknown.
141
Studies have indicated that in vitro resistance may be indicative of clinical failure (8, 18,
142
19). The results from other laboratories and institutions are needed to confirm our
143
observations.
144 145
TRANSPARENCY DECLARATION
146
NPW has received research support from Pfizer, Merck, Basilea, Astellas, Viamet,
147
bioMerieux, and Medicis, and has served on advisory boards for Merck, Astellas,
148
Toyama, and Viamet.
149 150
ACKNOWLEDGEMENTS
151
This work was presented, in part, at the 53rd Interscience Conference on Antimicrobial
152
Agents and Chemotherapy (Denver, CO, 2013). The authors would like to thank Carmita
153
Sanders for her assistance with this work.
154 155
REFERENCES
156
1.
CLSI. 2012. Reference Method for Broth Dilution Antifungal Susceptibility
157
Testing of Yeasts; Fourth Informational Supplement. CLSI document M27-S4.
158
Clinical and Laboratory Standards Institute, Wayne, PA.
159
2.
Pfaller MA, Andes D, Diekema DJ, Espinel-Ingroff A, Sheehan D, Testing
160
CSfAS. 2010. Wild-type MIC distributions, epidemiological cutoff values and
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species-specific clinical breakpoints for fluconazole and Candida: time for
7
162
harmonization of CLSI and EUCAST broth microdilution methods. Drug Resist
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Update 13:180-195.
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3.
Pfaller MA, Diekema DJ, Andes D, Arendrup MC, Brown SD, Lockhart SR,
165
Motyl M, Perlin DS, Testing CSfA. 2011. Clinical breakpoints for the
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echinocandins and Candida revisited: integration of molecular, clinical, and
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microbiological data to arrive at species-specific interpretive criteria. Drug Resist
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Update 14:164-176.
169
4.
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Pfaller MA. 2012. Antifungal drug resistance: mechanisms, epidemiology, and consequences for treatment. Am J Med 125:S3-13.
5.
CLSI. 2008. Reference method for broth dilution antifungal susceptibility testing
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of yeasts; Approved standard - Third Edition. CLSI document M27-A3. Clinical
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and Laboratory Standards Institute, Wayne, PA.
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6.
Pfaller MA, Messer SA, Woosley LN, Jones RN, Castanheira M. 2013.
175
Echinocandin and triazole antifungal susceptibility profiles for clinical
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opportunistic yeast and mold isolates collected from 2010 to 2011: application of
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new CLSI clinical breakpoints and epidemiological cutoff values for
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characterization of geographic and temporal trends of antifungal resistance. J Clin
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Microbiol 51:2571-2581.
180
7.
Pfaller MA, Boyken LB, Hollis RJ, Kroeger J, Messer SA, Tendolkar S,
181
Diekema DJ. 2011. Validation of 24-hour posaconazole and voriconazole MIC
182
readings versus the CLSI 48-hour broth microdilution reference method:
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application of epidemiological cutoff values to results from a global Candida
184
antifungal surveillance program. J Clin Microbiol 49:1274-1279.
8
185
8.
Alexander BD, Johnson MD, Pfeiffer CD, Jimenez-Ortigosa C, Catania J,
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Booker R, Castanheira M, Messer SA, Perlin DS, Pfaller MA. 2013.
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Increasing echinocandin resistance in Candida glabrata: clinical failure correlates
188
with presence of FKS mutations and elevated minimum inhibitory concentrations.
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Clin Infect Dis 56:1724-1732.
190
9.
Pfaller MA, Diekema DJ, Sheehan DJ. 2006. Interpretive breakpoints for
191
fluconazole and Candida revisited: a blueprint for the future of antifungal
192
susceptibility testing. Clin Microbiol Rev 19:435-447.
193
10.
Cuesta I, Bielza C, Cuenca-Estrella M, Larranaga P, Rodriguez-Tudela JL.
194
2010. Evaluation by data mining techniques of fluconazole breakpoints
195
established by the Clinical and Laboratory Standards Institute (CLSI) and
196
comparison with those of the European Committee on Antimicrobial
197
Susceptibility Testing (EUCAST). Antimicrob Agents Chemother 54:1541-1546.
198
11.
Clancy CJ, Yu VL, Morris AJ, Snydman DR, Nguyen MH. 2005. Fluconazole
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MIC and the fluconazole dose/MIC ratio correlate with therapeutic response
200
among patients with candidemia. Antimicrob Agents Chemother 49:3171-3177.
201
12.
Rodriguez-Tudela JL, Almirante B, Rodriguez-Pardo D, Laguna F, Donnelly
202
JP, Mouton JW, Pahissa A, Cuenca-Estrella M. 2007. Correlation of the MIC
203
and dose/MIC ratio of fluconazole to the therapeutic response of patients with
204
mucosal candidiasis and candidemia. Antimicrob Agents Chemother 51:3599-
205
3604.
9
206
13.
Panackal AA, Gribskov JL, Staab JF, Kirby KA, Rinaldi M, Marr KA. 2006.
207
Clinical significance of azole antifungal drug cross-resistance in Candida
208
glabrata. J Clin Microbiol 44:1740-1743.
209
14.
Pfaller MA, Messer SA, Boyken L, Rice C, Tendolkar S, Hollis RJ, Diekema
210
DJ. 2004. Cross-resistance between fluconazole and ravuconazole and the use of
211
fluconazole as a surrogate marker to predict susceptibility and resistance to
212
ravuconazole among 12,796 clinical isolates of Candida spp. J Clin Microbiol
213
42:3137-3141.
214
15.
Pfaller MA, Messer SA, Boyken L, Rice C, Tendolkar S, Hollis RJ, Diekema
215
DJ. 2007. Use of fluconazole as a surrogate marker to predict susceptibility and
216
resistance to voriconazole among 13,338 clinical isolates of Candida spp. Tested
217
by clinical and laboratory standards institute-recommended broth microdilution
218
methods. J Clin Microbiol 45:70-75.
219
16.
Pfaller MA, Messer SA, Boyken L, Tendolkar S, Hollis RJ, Diekema DJ.
220
2008. Selection of a surrogate agent (fluconazole or voriconazole) for initial
221
susceptibility testing of posaconazole against Candida spp.: results from a global
222
antifungal surveillance program. J Clin Microbiol 46:551-559.
223
17.
Pfaller MA, Messer SA, Rhomberg PR, Jones RN, Castanheira M. 2013. In
224
vitro activities of isavuconazole and comparator antifungal agents tested against a
225
global collection of opportunistic yeasts and molds. J Clin Microbiol 51:2608-
226
2616.
10
227
18.
Pfeiffer CD, Garcia-Effron G, Zaas AK, Perfect JR, Perlin DS, Alexander
228
BD. 2010. Breakthrough invasive candidiasis in patients on micafungin. J Clin
229
Microbiol 48:2373-2380.
230
19.
Baddley JW, Patel M, Bhavnani SM, Moser SA, Andes DR. 2008. Association
231
of fluconazole pharmacodynamics with mortality in patients with candidemia.
232
Antimicrob Agents Chemother 52:3022-3028.
233 234 235 236 237 238
11
239
TABLE 1. Previous and recently revised CLSI antifungal clinical breakpoints (CBP) for resistance for fluconazole, voriconazole,
240
anidulafungin, and micafungin against Candida species. Breakpoints are in μg/mL. The epidemiologic cut-off value was used for
241
voriconazole against C. glabrata. Previous or
C. albicans
C. glabrata
C. tropicalis
C. krusei
C. parapsilosis
Previous
>4
>4
>4
>4
>4
Revised
>1
> 0.5
>1
>1
>8
Previous
>4
>4
>4
>4
>4
Revised
>1
> 0.25
>1
>1
>8
Previous
> 64
> 64
> 64
> 64
> 64
Revised
>8
> 64
>8
>8
>8
Previous
>4
>4
>4
>4
>4
Revised
>1
>1
>1
>2
>1
revised CBP Anidulafungin
Micafungin
Fluconazole
Voriconazole
242
12
243
Table 2. MIC50 and MIC90 ranges and percentage of Candida albicans and Candida
244
glabrata isolates classified as resistant based on the previous and recently revised CLSI
245
clinical breakpoints for antifungals. AFG – anidulafungin, MFG – micafungin, FLU –
246
fluconazole, VOR - voriconazole Species
Candida albicans
Candida glabrata
Antifungal
AFG
MFG
FLU
VOR
AFG
MFG
FLU
VOR
No. Strains MIC Range
118
433
1196
593
110
354
882
522
MIC50
1
The Impact of New Antifungal Breakpoints on Antifungal Resistance in Candida
2
Species
3
Annette W. Fothergill, Deanna A. Sutton, Dora I. McCarthy, Nathan P. Wiederhold
4
Fungus Testing Laboratory, Department of Pathology, University of Texas Health
5
Science Center at San Antonio, San Antonio, TX
6 7
Abstract Word Count: 74
8
Keywords: antifungal breakpoints, Candida species, resistance
Manuscript Word Count: 1237
9 10
Corresponding Author:
11
Nathan P. Wiederhold, Pharm.D.
12
Associate Professor
13
UTHSCSA
14
Department of Pathology, MC 7750
15
7703 Floyd Curl Drive
16
San Antonio, TX 78229
17
Phone: 210-567-4086
18
Email: [email protected]
19 20 21 22 23
1
24
ABSTRACT
25
We reviewed our antifungal susceptibility data for micafungin, anidulafungin,
26
fluconazole, and voriconazole against Candida species, and compared resistance rates as
27
determined by the previous and recently revised CLSI antifungal breakpoints. With the
28
new breakpoints, resistance was significantly increased for micafungin (from 0.8% to
29
7.6%), anidulafungin (0.9% to 7.3%) and voriconazole (6.1% to 18.4%) against C.
30
glabrata. Resistance was also increased for fluconazole against C. albicans (2.1% to
31
5.7%).
32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
2
47
The Clinical and Laboratory Standards Institute (CLSI) recently revised the azole
48
and echinocandin clinical breakpoints against Candida species (1). These new
49
breakpoints are now both drug and species specific, whereas the previous breakpoints
50
were not. For most species, with the exception of C. parapsilosis and C. guilliermondii
51
against the echinocandins, the breakpoints have been lowered, such that previously
52
susceptible minimum inhibitory concentrations (MIC) are now classified as resistant. In
53
addition, C. glabrata isolates are no longer considered susceptible to fluconazole, but are
54
rather classified only as either susceptible dose-dependent or resistant. The breakpoint
55
revisions were made based on information from clinical studies, case reports describing
56
clinical failure at MIC values below the previous breakpoints, results from
57
pharmacokinetic/pharmacodynamics studies, and epidemiologic cut-off values (2, 3).
58
Additionally, a goal of harmonizing the antifungal breakpoints with those set by
59
EUCAST was sought. Epidemiologic cut-off values for individual species are used to
60
optimize the detection of non-wild type strains and thus the acquisition of resistance
61
mechanisms, and to prevent the breakpoints from dividing wild-type populations (2-4).
62
The impact of the revised clinical breakpoints regarding categorical placement of
63
Candida strains as resistant is unknown. Our objective was to evaluate what effect the
64
new antifungal clinical breakpoints may have on azole and echinocandin resistance
65
patterns in Candida species.
66
The antifungal susceptibility database in the Fungus Testing Laboratory at the UT
67
Health Science Center at San Antonio was reviewed. Susceptibility data for fluconazole,
68
voriconazole, anidulafungin, and micafungin against C. albicans, C. glabrata, C.
69
tropicalis, C. krusei, and C. parapsilosis isolates sent to our laboratory for testing
3
70
between January 1, 2008 and December 31, 2012 were reviewed. During this period,
71
antifungal powders were obtained from the appropriate manufacturers (Pfizer and
72
Astellas), and stock solutions were prepared in water for agents with aqueous solubility,
73
or in DMSO as recommended (1, 5). Susceptibility testing was performed by broth
74
microdilution methodology in RPMI according to the CLSI M27-A3 guidelines (5), and a
75
50% inhibition of growth compared to the growth control well was used as the endpoint
76
for all agents. Candida krusei ATCC 6258 and C. parapsilosis ATCC 22019 served as
77
the quality control isolates for each testing run, and the results were consistently within
78
the range specified by the CLSI. Isolates were classified as resistant based on both the
79
previous and recently revised CLSI clinical breakpoints (Table 1) (1). For voriconazole
80
against C. glabrata the epidemiologic cut-off value of 0.5 μg/mL was used for the new
81
threshold for resistance, as the CLSI has not set clinical breakpoints for this triazole
82
against this species (1, 6, 7). Thus, C. glabrata isolates with a voriconazole MIC above
83
this value (i.e., > 1 μg/mL) were classified as resistant. Differences in resistance rates
84
between the previous and revised breakpoints were assessed for significance by Fischer’s
85
exact test, and a p-value of < 0.05 was considered to be significant.
86
The number of each Candida species tested with each drug, the MIC range,
87
MIC50 and MIC90 values, and the percent of isolates classified as resistant per the
88
previous and revised breakpoints are shown in Table 2, and the MIC distributions are
89
shown in Table 3. As shown in this table and in Figure 1, resistance did increase with the
90
new breakpoints. For the echinocandins anidulafungin and micafungin, the most marked
91
changes occurred against C. glabrata. For this species, the number of isolates classified
92
as resistant increased from 1 (0.9%) to 8 (7.3%) of 110 isolates (p = 0.0353) for
4
93
anidulafungin and from 3 (0.8%) to 27 (7.6%) of 354 isolates (p < 0.0001) for
94
micafungin when the new CLSI clinical breakpoints were applied. Our rates of
95
micafungin and anidulafungin resistance with the new CLSI clinical breakpoints are
96
higher than those recently reported in the SENTRY study (1.3% and 1.6%, respectively)
97
(6). However, others have found higher rates of echinocandin resistance for this species,
98
with rates of micafungin and anidulafungin resistance reported to range from 9% to 12%
99
between 2007 and 2010 at a large medical center in the U.S. (8). Against the other
100
Candida species, the number of isolates considered to be resistant remained relatively
101
low, and for anidulafungin against C. parapsilosis, the number actually decreased slightly
102
from 2 to 0 isolates (2.4% to 0%), although this reduction was not statistically significant.
103
This was not unexpected against this species, as the CLSI echinocandin breakpoints
104
against C. parapsilosis were raised from > 4 μg/mL as non-susceptible to > 8 μg/mL as
105
resistant.
106
The azoles fluconazole and voriconazole were also affected by the revised
107
breakpoints. Against C. albicans, the number of isolates classified as resistant to
108
fluconazole by the new breakpoints significantly increased from 25 (2.1%) to 68 (5.7%)
109
of a total of 1196 strains tested (p < 0.0001; Table 2 and Figure 1) compared to the
110
previous threshold for resistance. This rate of fluconazole resistance in C. albicans is
111
higher than what was recently reported in isolates from North American institutions in
112
the SENTRY study (0.6%) (6). There were also trends for increased resistance to
113
fluconazole with the new breakpoints against C. tropicalis (19 to 32 of 327 isolates [6%
114
to 9.9%]; p = 0.0557) and C. parapsilosis (3 to 11 of 497 isolates [0.6% to 2.2%]; p =
115
0.0793). A similar observation was also found for voriconazole against C. albicans (17
5
116
to 27 of 593 isolates [2.9% to 4.6%]; p = 0.17), although this difference was not
117
significant. In contrast, only minor increases in voriconazole resistance against C.
118
tropicalis (30 to 36 of 205 isolates [14.6% to 17.6%]), and C. krusei (4 to 7 of 98 isolates
119
[4.1% to 12.2%]) were observed when the new breakpoints were applied. A significant
120
increase in the number of C. glabrata isolates that were classified as resistant to
121
voriconazole (32 to 96 of 522 isolates [6.1% to 18.4%]; p < 0.0001) was observed when
122
the epidemiologic cut-off value was used. The revised CLSI breakpoints for the azoles
123
are supported by epidemiologic cut-off values and the results of various
124
pharmacodynamics analyses (9-12), as well as by the cross-resistance observed among
125
different members of this class in Candida species (13-16). For most species, our rates of
126
fluconazole and voriconazole resistance were higher than those reported in the SENTRY
127
study (6). This may be a reflection of the nature of our reference laboratory in that we
128
may often be sent isolates from patients exposed to antifungals who are failing therapy.
129
Thus, some of the isolates we receive for susceptibility testing may be more likely be
130
non-wild type strains. However, the overall MIC distributions from our study shown in
131
Table 3 are similar to those reported by others including those from large surveillance
132
studies (6, 7, 17).
133
The results from our laboratory demonstrate that the rates of resistance for the
134
echinocandins and the azoles may be increased with the use of the new CLSI antifungal
135
breakpoints. These changes were especially marked for micafungin, anidulafungin, and
136
voriconazole against C. glabrata and for fluconazole against C. albicans. One limitation
137
of this study is that we did not determine if the isolates harbored mechanisms of acquired
138
antifungal resistance. Although this information is important, it would not change how
6
139
an isolate is classified as susceptible or resistant by the CLSI breakpoints, which is
140
determined by the phenotypic MIC. The clinical relevance of our findings is unknown.
141
Studies have indicated that in vitro resistance may be indicative of clinical failure (8, 18,
142
19). The results from other laboratories and institutions are needed to confirm our
143
observations.
144 145
TRANSPARENCY DECLARATION
146
NPW has received research support from Pfizer, Merck, Basilea, Astellas, Viamet,
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bioMerieux, and Medicis, and has served on advisory boards for Merck, Astellas,
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Toyama, and Viamet.
149 150
ACKNOWLEDGEMENTS
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This work was presented, in part, at the 53rd Interscience Conference on Antimicrobial
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Agents and Chemotherapy (Denver, CO, 2013). The authors would like to thank Carmita
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Sanders for her assistance with this work.
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TABLE 1. Previous and recently revised CLSI antifungal clinical breakpoints (CBP) for resistance for fluconazole, voriconazole,
240
anidulafungin, and micafungin against Candida species. Breakpoints are in μg/mL. The epidemiologic cut-off value was used for
241
voriconazole against C. glabrata. Previous or
C. albicans
C. glabrata
C. tropicalis
C. krusei
C. parapsilosis
Previous
>4
>4
>4
>4
>4
Revised
>1
> 0.5
>1
>1
>8
Previous
>4
>4
>4
>4
>4
Revised
>1
> 0.25
>1
>1
>8
Previous
> 64
> 64
> 64
> 64
> 64
Revised
>8
> 64
>8
>8
>8
Previous
>4
>4
>4
>4
>4
Revised
>1
>1
>1
>2
>1
revised CBP Anidulafungin
Micafungin
Fluconazole
Voriconazole
242
12
243
Table 2. MIC50 and MIC90 ranges and percentage of Candida albicans and Candida
244
glabrata isolates classified as resistant based on the previous and recently revised CLSI
245
clinical breakpoints for antifungals. AFG – anidulafungin, MFG – micafungin, FLU –
246
fluconazole, VOR - voriconazole Species
Candida albicans
Candida glabrata
Antifungal
AFG
MFG
FLU
VOR
AFG
MFG
FLU
VOR
No. Strains MIC Range
118
433
1196
593
110
354
882
522
MIC50
