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Journal of Clinical Microbiology, January 1998, p. 153-156, Vol. 36, No. 1
University of Texas Health Science Center at
San Antonio1 and
Audie Murphy
Division, South Texas Veterans Health Care
System,2 San Antonio, Texas
Received 14 July 1997/Returned for modification 22 September
1997/Accepted 10 October 1997
Trailing endpoints remain a problem in antifungal susceptibility
testing using the National Committee for Clinical Laboratory Standards
(NCCLS) method. For isolates for which trailing endpoints are found,
MICs of
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Interpretation of Trailing Endpoints in Antifungal
Susceptibility Testing by the National Committee for Clinical
Laboratory Standards Method
1 µg/ml at 24 h and of >64 µg/ml at 48 h are usually observed. In a study of human immunodeficiency virus
(HIV)-infected patients with oropharyngeal candidiasis, we identified
three patients with multiple serial isolates for which trailing
endpoints were observed with fluconazole. At 24 h, MICs were
generally
1 µg/ml by both broth macro- and microdilution methods.
However, at 48 h, MICs were >64 µg/ml, while the organism
remained susceptible by agar dilution testing with fluconazole. Most
episodes of oropharyngeal candidiasis with trailing-endpoint isolates
responded to doses of fluconazole as low as 100 mg/day. Two patients
had both susceptible and trailing-endpoint isolates by NCCLS broth
macro- and microdilution testing; these isolates were found to be the
same strain by pulsed-field gel electrophoresis using restriction
fragment length polymorphisms. Another patient had two different
strains, one for which trailing endpoints were observed and one which
was susceptible at 48 h. Trailing endpoints may be seen with
selected isolates of a strain or may be a characteristic finding for
most or all isolates of a strain. In addition, with isolates for which
trailing endpoints are observed, reading the endpoint for the NCCLS
method at 24 h may be more appropriate.
*
Corresponding author. Mailing address: University of
Texas Health Science Center at San Antonio, Department of
Medicine/Infectious Diseases, 7703 Floyd Curl Dr., San Antonio, TX
78284-7881. Phone: (210) 567-4823. Fax: (210) 567-3303. E-mail:
REVANKAR{at}UTHSCSA.EDU.
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