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Journal of Clinical Microbiology, Sep 1995, 2316-2323, Vol 33, No. 9
JR Johnson, FS Tiu and WE Stamm
Despite its theoretical advantages, direct antimicrobial susceptibility
testing (DST) of urine specimens remains controversial largely because of
concerns regarding its accuracy, particularly with mixed cultures. To
evaluate the performance of DST in the setting of acute urinary tract
infection (UTI), we performed DST using 25 traditional and contemporary
antimicrobial agents on urine specimens from 162 women with suspected acute
uncomplicated UTI, and compared these results with the results of
standardized disk diffusion susceptibility tests done on the same
specimens. Direct tests were interpretable for 129 specimens, i.e., 80% of
all specimens and 85% of the 152 specimens that met the culture criteria
for UTI. Of the 2,983 individual comparisons between the direct and
standard tests, 0.8% represented very major errors, 0.6% represented major
errors, 3.1% represented minor errors, and 95.5% were in agreement. Errors
were more common in association with older antimicrobial agents and agents
with a high prevalence of antimicrobial resistance, non-Escherichia coli
strains, low urine bacterial concentrations, sparse or mixed growth in the
direct test, and the presence of multiple significant organisms in urine.
The urine leukocyte concentration was > or = 15/mm3 in all subjects and
did not differentiate between specimens that gave an interpretable direct
test and those that did not. Calculation of the sensitivity of DST in
identifying antimicrobial resistance supplemented conventional error rate
analysis. We conclude that when used selectively and interpreted carefully,
DST of urine specimens offers an efficient, rapid, and accurate method for
antimicrobial susceptibility determination for acute UTI, particularly when
the urine bacterial concentration is > 10(5) CFU/ml.
Copyright © 1995 by the American Society for Microbiology. All rights reserved.
Direct antimicrobial susceptibility testing for acute urinary tract infections in women
Department of Medicine, University of Minnesota, Minneapolis, USA.
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