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Journal of Clinical Microbiology, October 1998, p. 2882-2886, Vol. 36, No. 10
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Direct Antimicrobial Susceptibility Testing of
Gram-Negative Bacilli in Blood Cultures by an Electrochemical
Method
Ay Huey
Huang,1
Jiunn Jong
Wu,2
Yu Mei
Weng,2
Hwia Cheng
Ding,3 and
Tsung Chain
Chang2,*
Division of Clinical Microbiology, Department
of Pathology, National Cheng Kung University
Hospital,1 and
Department of Medical
Technology, National Cheng Kung University Medical College, Tainan
701,2 and
Food Industry Research and
Development Institute, Hsinchu 300,3 Taiwan,
Republic of China
Received 3 March 1998/Returned for modification 22 May
1998/Accepted 13 July 1998
 |
ABSTRACT |
Nonfastidious aerobic gram-negative bacilli (GNB) are commonly
isolated from blood cultures. The feasibility of using an
electrochemical method for direct antimicrobial susceptibility testing
of GNB in positive blood cultures was evaluated. An aliquot (10 µl)
of 1:10-diluted positive blood cultures containing GNB was inoculated into the Bactometer module well (bioMérieux Vitek, Hazelwood, Mo.) containing 1 ml of Mueller-Hinton broth supplemented with an
antibiotic. Susceptibility tests were performed in a breakpoint broth
dilution format, with the results being categorized as resistant, intermediate, or susceptible. Seven antibiotics (ampicillin,
cephalothin, gentamicin, amikacin, cefamandole, cefotaxime, and
ciprofloxacin) were used in this study, with each agent being tested at
the two interpretive breakpoint concentrations. The inoculated modules were incubated at 35°C, and the change in impedance in each well was
continuously monitored for 24 h by the Bactometer. The MICs of the
seven antibiotics for each blood isolate were also determined by the
standardized broth microdilution method. Of 146 positive blood cultures
(1,022 microorganism-antibiotic combinations) containing GNB tested by
the direct method, the rates of very major, major, and minor errors
were 0, 1.1, and 2.5%, respectively. The impedance method was simple;
no centrifugation, preincubation, or standardization of the inocula was
required, and the susceptibility results were normally available within
3 to 6 h after inoculation. The rapid method may allow proper
antimicrobial treatment almost 30 to 40 h before the results of
the standard methods are available.
| |
INTRODUCTION |
The isolation of any significant
microorganism from a blood culture is an occurrence that requires
careful evaluation by the clinician, and prompt action is usually
necessary. If the results of clinical microbiological analyses are to
contribute in a meaningful way to the diagnosis and management of
patients with bacteremia, they must be made available to the clinician
in a relevant time frame (1, 3, 15).
Most clinical laboratories use liquid media for the detection of
microorganisms in blood, and the antimicrobial susceptibility tests are
performed with colonies obtained on subculture plates. After a positive
blood culture is detected, the standard procedures may take as long as
2 days to provide the susceptibility results. Recognizing this, efforts
have been made to devise analytical procedures which can provide
results more quickly.
Rapid techniques for testing the susceptibilities of organisms in blood
cultures include the direct disk diffusion test (3, 4, 9, 11,
16) and automated or semiautomated instrument systems. Direct
disk diffusion susceptibility testing of the organisms in positive
blood cultures has been shown to be reliable for most microorganisms
and antimicrobial agents (4, 6, 16, 24); this technique can
save 18 to 24 h compared to the times required for the
standardized protocols. Additional time savings can be obtained by
early reading (6 to 10 h) of the plates after direct incubation
(1, 12, 13); however, the test accuracy is sacrificed and
some plates may not be readable due to limited bacterial growth.
Several automated systems for antimicrobial susceptibility testing have
been described. These systems include the Vitek system (bioMérieux Vitek, Hazelwood, Mo.) (17, 20, 22),
MicroScan (Baxter MicroScan, West Sacramento, Calif.) (14,
22), and the MS-2 system (Abbott Laboratories, Irving, Tex.)
(2, 19). Although direct inoculation of positive blood
culture broths into these systems has been suggested, serial steps of
blood cell lysis, differential centrifugation, or preincubation in a
broth followed by adjustment of the inoculum are recommended before
inoculation. These additional procedures are subject to contamination
and are impractical for routine analyses.
A novel method that uses electrochemical measurement was recently
proposed for the direct detection of oxacillin-resistant Staphylococcus aureus in blood culture bottles
(25). The method is based on the phenomenon that electrical
changes (e.g., impedance, conductance, or capacitance) will occur in
the media, provided that the test microorganism can grow to a
population of approximately 106 to 107 CFU/ml
(7). The method is simple and rapid and has a high degree of
accuracy.
The purpose of this study was to evaluate the feasibility of direct
antimicrobial susceptibility testing of nonfastidious aerobic
gram-negative bacilli (GNB) in positive blood cultures by the
electrochemical method.
| |
MATERIALS AND METHODS |
Selection of electrical signal for susceptibility testing.
The measurement of electrical changes in the culture broth was
conducted with the Bactometer M-128 (bioMérieux Vitek)
instrument. Three electrical signals (impedance, conductance, and
capacitance) were available from the instrument. To determine which
signal was best for monitoring the bacterial growth, the three signals were obtained for two clinical isolates (Escherichia coli
1966 and Klebsiella pneumoniae 1374). Each module
(bioMérieux Vitek) well contained 1 ml of Mueller-Hinton broth
and was inoculated with 50 µl of a 1:10-diluted bacterial suspension
with a turbidity equivalent to that of a 0.5 McFarland standard. The
inoculated modules (each module contained 16 wells) were inserted into
the Bactometer incubator set at 35°C. The change in the electrical signals in the module wells was continuously monitored by the instrument at 6-min intervals for 24 h, and the results were
graphically displayed as the percent changes in the three signals.
The detection time (DT; in hours) for each module well was
automatically determined by the instrument software when three consecutive readings of the signal change exceeded the default value in
the instrument or was manually determined by locating the inflection
point (where an accelerating change in the signal was evident) on the
growth curve.
Validation of the electrochemical method for susceptibility
testing.
To verify the electrochemical technique for
susceptibility testing, the MICs for 5 strains of GNB were determined
with the Bactometer, with each strain being tested against two randomly selected antimicrobial agents. The strains (antibiotics) tested were
E. coli ATCC 23501 (cephalothin and gentamicin),
Pseudomonas aeruginosa ATCC 27853 (gentamicin and amikacin),
K. pneumoniae 9367 (gentamicin and ciprofloxacin),
Enterobacter cloacae 9950 (cephalothin and amikacin), and
Citrobacter freundii 8311 (amikacin and ciprofloxacin). The
procedures were the same as those described above, except that the
culture broth was supplemented with various concentrations of an
antimicrobial agent and impedance was used to monitor the growth of the
bacteria. The MIC was defined as the lowest concentration of an
antibiotic that completely abolished the change in the impedance during
an incubation period of 20 h at 35°C.
Direct susceptibility testing of positive blood cultures.
Blood specimens were collected at the National Cheng Kung University
Hospital during a 6-month period in 1997. The BACTEC Aerobic and
Aerobic Plus bottles (Becton Dickinson Microbiology Systems, Sparks,
Md.) were normally inoculated with 5 to 10 ml of blood from the
patients, inserted into BACTEC NR-9240 instruments (Becton Dickinson
Microbiology Systems), and incubated at 37°C. Samples from positive
bottles showing growth of GNB, as determined by Gram staining, were
used for direct inoculation into the Bactometer. Smears showing mixed
cultures were excluded from the study.
Seven antimicrobial agents were used for susceptibility testing, with
each agent being tested at the two interpretive breakpoint concentrations (ampicillin, cephalothin, and cefamandole, 8 and 32 µg/ml; gentamicin, 4 and 16 µg/ml; amikacin, 16 and 64 µg/ml; cefotaxime, 8 and 64 µg/ml; ciprofloxacin, 1 and 4 µg/ml) as
defined by the National Committee for Clinical Laboratory Standards
(18). The positive culture broths containing GNB were
diluted 1:10 with sterile water, and 10 µl of the diluted samples was
inoculated into each module well. The inoculated modules were incubated
at 35°C. A positive control (no antibiotic in the inoculated well) and a negative control (culture broth only) were included in tests with
each blood specimen. Interpretive categorization of the blood isolate
by the direct method was based on the inhibition of the microorganism
at the two breakpoint concentrations (18).
All blood isolates obtained on subculture plates were identified by
conventional microbiological procedures. The MICs of the
seven
antimicrobial agents for each isolate were determined by
the
standardized broth microdilution method (
18). The MIC data
for each isolate were used for categorization of the interpretive
susceptibility (
18).
Analysis of discrepancy.
The results from the direct
impedance tests were compared with those from the microdilution method,
and discrepancies were classified as very major, major, or minor errors
(4). A very major error was a susceptible result by the
direct method and a resistant result by the standard method. A major
error was a resistant result by the direct method and a susceptible
result by the standard method. A minor error was any change involving an intermediate result.
| |
RESULTS |
Selection of electrical signal.
The growth curves for E. coli 1966, as monitored with the three electrical signals, are
shown in Fig. 1. Usually, the capacitance change during the growth of bacteria was most prominent, followed by
changes in the impedance and conductance. However, the DTs (2.5 h) were
not influenced by the use of any of these signals. Similar results were
obtained for K. pneumoniae 1374 (data not shown). For some
GNB isolates, the change in the capacitance signal was so large that an
overscale response was encountered, whereas the change in the
conductance signal for some strains (e.g., Acinetobacter and
Stenotrophomonas) was too small to reveal active growth.
Therefore, the impedance signal was used in the following
susceptibility experiments.
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FIG. 1.
Growth curves for E. coli 1966 (a clinical
isolate) as measured by the changes in capacitance (curve A), impedance
(curve B), and conductance (curve C). The change in the capacitance
signal was most prominent, followed by changes in the impedance and
conductance signals.
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Validation of the impedance method for susceptibility testing.
At the beginning of the study, it was necessary to prove that the MICs
determined by the electrochemical method were comparable to those
obtained by standardized procedures. The comparison was conducted with
five strains of GNB (E. coli, P. aeruginosa,
K. pneumoniae, E. cloacae, and C. freundii), with each strain being tested with two randomly
selected antibiotics. It appeared that the MICs determined by the
impedance method were comparable or equivalent to those obtained by the
microdilution method (Table 1).
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TABLE 1.
Comparison of the MICs for five strains of GNB determined
by the impedance method and the broth microdilution method
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Direct antimicrobial susceptibility testing by the impedance
method.
A total of 150 positive blood cultures containing GNB were
analyzed by the impedance method, with each culture being tested with
seven antibiotics. Among the 150 blood cultures, 4 samples contained
mixed cultures and were excluded from the data analysis. The
distribution of microorganisms in the 146 blood cultures is shown in
Table 2, with E. coli (51 strains; 35%) being the most frequently occurring isolate, followed by
K. pneumoniae (29 strains; 19.8%) P. aeruginosa
(14 strains; 9.6%), E. cloacae (10 strains; 6.8%), and
other minor species.
Figure
2 shows typical growth curves
obtained with the impedance signal and generated by direct inoculation
of a positive
blood culture into the Bactometer. The impedance
measurement was
obtained by a real-time, on-line process. It was
evident that
the strain in the culture bottle (
E. coli 8892)
was resistant
to ampicillin (32 µg/ml; curve B) and ciprofloxacin (4 µg/ml;
curve C) but was susceptible to gentamicin (16 µg/ml; curve
D).
The DT for the positive control (no antibiotic in the inoculated
well; curve A) was only 2.3 h, and at about this time the
susceptibility
of the organism to other antibiotics was readily
discernible.
Since most aerobic GNB from blood cultures were
fast-growing organisms,
the antimicrobial susceptibility patterns were
normally available
within 3 to 6 h after direct inoculation into
the Bactometer.
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FIG. 2.
Antimicrobial susceptibility patterns generated by
direct inoculation of a positive blood culture into the Bactometer. The
growth curves were monitored by detecting changes in impedance during
incubation. It was evident that the microorganism (E. coli
8892) in the blood culture was resistant to ampicillin (curve B) and
ciprofloxacin (curve C) but susceptible to gentamicin (curve D). It is
noteworthy that the DT for the positive control (no antibiotic in the
inoculated well; curve A) was only 2.3 h.
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Occasionally, a long delay in DT compared with that for the positive
control was found for some blood samples (Fig.
3); this
indicated the presence of a
heterogeneous resistant subpopulation
in the blood cultures. For
example, the isolate for which data
are presented in Fig.
3 (
E. cloacae 0333) was resistant to gentamicin
(16 µg/ml; curve B),
cefamandole (32 µg/ml; curve C), and cefotaxime
(64 µg/ml; curve
D); however curves C and D had DTs of 9.0 and
10.3 h,
respectively. The lag in DTs was about 6 h compared to
that for
the positive control (DT, 3.5 h). The microorganisms
in the module
wells containing cefamandole and cefotaxime were
subcultured, and the
MICs were determined to be 128 and 512 µg/ml,
respectively, by the
microdilution method. In contrast, the MICs
of cefamandole and
cefotaxime were only 16 and 1.0 µg/ml, respectively,
for colonies
obtained after subculture of the positive blood culture
on an agar
plate. The discrepancies caused by the direct inoculation
method and
the conventional method would be that the resistant
subpopulation,
which represented only a minor population in the
original bottle, grew
to a majority in the presence of an antibiotic.
However, the minor
resistant bacteria had little chance of being
sampled for MIC
determination after subculture on an agar plate.
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FIG. 3.
Detection of minor resistant subpopulation by direct
inoculation of a positive blood culture into the Bactometer. The blood
isolate (E. cloacae 0333) was resistant to gentamicin (curve
B), cefamandole (curve C), and cefotaxime (curve D). However, the DTs
in the presence of cefamandole (9 h) and cefotaxime (10.3 h) were much
longer than that (3.5 h) for the positive control. The MICs
(cefamandole, 128 µg/ml; cefotaxime, 512 µg/ml) determined for
subcultures obtained from the module wells were much higher than those
(cefamandole, 16 µg/ml; cefotaxime, 1 µg/ml) for organisms
subcultured from the original blood bottle. The detection time of
positive control (curve A) was 3.5 h.
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When 146 blood cultures containing aerobic GNB were tested against the
seven antimicrobial agents (a total of 1,022 microorganism-antibiotic
combinations) by the impedance method and the microdilution technique,
the overall agreement between the two methods in terms of the
interpretive categories (susceptible, intermediate, and resistant)
was
96.4%. There were 11 (1.1%) major errors and 26 (2.5%) minor
errors
caused by the direct method, but no very major error was
found. The
major discrepancies were observed for strains of
E. coli,
E. cloacae,
Acinetobacter spp., and
Stenotrophomonas maltophilia when testing cefamandole,
cefotaxime, or aminoglycosides (gentamicin
and amikacin) (Table
3).
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TABLE 3.
Results of major errors caused by the impedance method
after testing 146 positive cultures containing nonfastidious
aerobic GNB with seven antibiotics
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|
Among the 26 minor errors produced by the direct method, 19 were false
resistance, with the remaining 7 being false susceptibility.
Of these
minor errors, 21 were observed when testing
-lactam
antibiotics,
with the frequencies of occurrence being as follows:
ampicillin, three
samples; cephalothin, six samples; cefamandole,
eight samples;
cefotaxime, five samples; and other antibiotics,
four samples. No
specific microorganism-antibiotic combination
was responsible for these
minor discrepancies. The major and minor
errors caused by the direct
method were reconfirmed by testing
the colonies grown on subculture
plates by the E test (AB Biodisk,
Solna, Sweden).
Susceptibility tests with mixed cultures.
Although smears
apparently containing mixed cultures were not used in the direct
susceptibility test, four blood samples appeared to contain multiple
species, as revealed on subculture plates and identified by
conventional procedures. Three of the four specimens contained two
different species of GNB, with the remaining specimen containing two
different strains of E. coli. Table
4 demonstrates the susceptibility test
results for two of the four mixed cultures. When a polymicrobial
infection was encountered, the impedance method detected the more
resistant side of the mixed flora. For example, a mixed blood culture
(specimen 9758) contained E. coli (cephalothin resistant)
and K. pneumoniae (cephalothin susceptible), and the
impedance method detected resistance when cephalothin was tested.
| |
DISCUSSION |
A direct antimicrobial susceptibility test based on the
measurement of changes in impedance was developed for blood cultures containing aerobic GNB. The method was performed in a breakpoint broth
dilution format with results expressed in the form of susceptibility categories (resistant, intermediate, and susceptible). Under most conditions, the susceptibility results were available within 3 to
6 h after inoculation by the direct method, whereas by routine procedures results are available in an average of 40 to 48 h. This
allowed the susceptibility patterns to be available on the same day
that the positive blood culture bottles were detected in the clinical
laboratories. The direct method had a level of agreement of 96.4% with
the standardized microdilution technique performed with pure cultures
grown on subculture plates. The frequencies of major errors (1.1%) and
minor errors (2.5%) by the impedance method were low.
The impedance technique described here was simple; only a single step
of inoculating 10 µl of a 1:10-diluted positive culture broth into
the module wells was required. Among the seven antimicrobial agents
tested, ampicillin, cephalothin, and gentamicin represented group A
antibiotics, with the remaining four (amikacin, cefamandole, cefotaxime, and ciprofloxacin) being group B antibiotics; both groups
are recommended by the National Committee for Clinical Laboratory
Standards for routine testing and reporting (18).
Since trimethoprim-sulfamethoxazole is also commonly used for the
treatment of bacteremia caused by GNB, at the end of this study 28 blood cultures containing GNB were tested with this antimicrobial agent
combination. The results demonstrated that the direct method had only
one minor error and a 96.3% agreement with the reference microdilution
method (data not shown). It seems that the impedance method can be
applied to a broad spectrum of microorganisms and antimicrobial agents.
The impact of rapid antimicrobial susceptibility testing on infectious
disease outcome has been systematically assessed by Doern et al.
(5). The benefits include significant reductions in the
numbers of microbiology tests, subsequent positive blood cultures,
serum antibiotic assays, some imaging procedures, and days of
intubation and reductions in the length of time spent in an intensive
care area. It was important to find that the mortality rate was much
lower (8.8%) for the rapid test group than for the control group
(15.3%) for which conventional overnight techniques were used for
susceptibility testing (5). Trenholme et al. (21)
also demonstrated that rapid susceptibility testing of blood isolates
could result in an earlier initiation of an appropriate therapy or a
change to the use of more effective and less expensive antibiotics. In
addition, the rapid availability of susceptibility information was more
likely to be followed by the treatment of patients by clinicians.
Direct disk diffusion susceptibility testing of the organisms found in
blood cultures has been shown to be reliable for most microorganism-antimicrobial agent combinations (6, 16, 24). Before direct inoculation, some investigators proposed that positive blood samples should be subcultured in a liquid broth followed by
adjustment of the inoculum density. However, several studies with
inocula taken directly from positive blood bottles also obtained good
results (3, 4), but an incubation period of 16 to 20 h
is normally required for the direct disk diffusion test.
Several instrument-assisted susceptibility test systems have been
developed, and these systems were claimed to provide results in a
matter of hours rather than days. These instruments include MicroScan,
the Vitek Automicrobic system, and the Cobasbact system (10, 14,
21-23). However, several steps including sample centrifugation, blood cell lysis, and standardization of the inoculum are recommended before direct inoculation into these systems (2, 19, 20), or
a preincubation step followed by adjustment of the inoculum density is
required (11). The detection principles for these systems
are usually based on the measurement of changes in optical properties
(turbidity or fluorescence) and are more sensitive to interferences
from the blood specimens.
The present impedance method has two advantages. The first is that the
measurement of an electrical property was basically not influenced by
the color or turbidity of the blood samples. The second was that signal
detection in the Bactometer was a continuous, real-time process, and
susceptibility patterns could be obtained by a real-time comparison
with the growth curve for the positive control.
Direct susceptibility testing has an additional advantage for the
testing of a broader representation of the bacterial population present
in blood cultures (8) and is more likely to detect the
heterogeneous resistant bacteria which represent only a minor subpopulation in positive blood culture bottles. Theoretically, about
105 cells were inoculated into each module well of the
Bactometer, whereas only three to five colonies on subculture plates
were sampled for inoculum preparation by the conventional microdilution protocol (18). This might explain the observation that on
most occasions in which discrepant results occurred the direct method detected the more-resistant organism of the mixed cultures and very
major errors were not found.
Although polymicrobial infections were excluded from the data analysis
in this study, it was interesting that the impedance method detected
the more resistant side of the mixed flora (Table 4). This result would
be desirable if the direct method were used to guide a clinician in
starting antimicrobial therapy for patients.
In view of the high rate of isolation of aerobic GNB from patients with
bacteremia and the high mortality rates from bacteremia caused by
aerobic GNB, a rapid method for the antimicrobial susceptibility testing of GNB may be beneficial for patients with bacteremia. The
impedance method is proposed as a test that can be used as a supplement
to the standardized procedures for the earlier determination of the
susceptibility patterns of aerobic GNB from blood cultures.
| |
ACKNOWLEDGMENTS |
This project was supported by a grant (grant NSC
88-2314-B-006-078) from the National Science Council, Taipei, Taiwan,
and by a grant (NCKUH 87-065) from National Cheng Kung University Hospital, Tainan, Taiwan, Republic of China.
| |
FOOTNOTES |
*
Corresponding author. Mailing address: Department of
Medical Technology, National Cheng Kung University Medical College, 1 University Rd., Tainan 701, Taiwan, Republic of China. Phone: 886-6-2353535, ext. 5790. Fax: 886-6-2363956. E-mail:
tsungcha{at}mail.ncku.edu.tw.
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REFERENCES |
| 1.
|
Coyle, M. B.,
L. A. McGonagle,
J. J. Plorde,
C. R. Clausen, and F. D. Schoenknecht.
1984.
Rapid antimicrobial susceptibility testing of isolates from blood cultures by direct inoculation and early reading of disk diffusion tests.
J. Clin. Microbiol.
20:473-477[Abstract/Free Full Text].
|
| 2.
|
Dipersio, J. R.,
S. M. Ficorilli, and F. J. Varga.
1984.
Direct identification and susceptibility testing of gram-negative bacilli from BACTEC bottles by use of the MS-2 system with updated bacterial identification software.
J. Clin. Microbiol.
20:1202-1204[Abstract/Free Full Text].
|
| 3.
|
Doern, G. V.,
D. R. Scott, and A. L. Rashad.
1982.
Clinical impact of rapid antimicrobial susceptibility testing of blood culture isolates.
Antimicrob. Agents Chemother.
21:1023-1024[Abstract/Free Full Text].
|
| 4.
|
Doern, G. V.,
D. R. Scott,
A. L. Rashad, and K. S. Kim.
1981.
Evaluation of a direct blood culture disk diffusion antimicrobial susceptibility test.
Antimicrob. Agents Chemother.
20:696-698[Abstract/Free Full Text].
|
| 5.
|
Doern, G. V.,
R. Vautour,
M. Gaudet, and B. Levy.
1994.
Clinical impact of rapid in vitro susceptibility testing and bacterial identification.
J. Clin. Microbiol.
32:1757-1762[Abstract/Free Full Text].
|
| 6.
|
Fay, D., and J. E. Oldfather.
1979.
Standardization of direct susceptibility test for blood cultures.
J. Clin. Microbiol.
9:347-350[Abstract/Free Full Text].
|
| 7.
|
Firstenberg-Eden, R., and G. Eden.
1984.
Impedance microbiology, p. 7-90.
John Wiley & Sons, Inc., New York, N.Y.
|
| 8.
|
Hong, T., and J. Ndamukong.
1996.
Direct application of Etest to gram-positive cocci from blood cultures: quick and reliable minimum inhibitory concentration data.
Diagn. Microbiol. Infect. Dis.
25:21-25[Medline].
|
| 9.
|
Johnson, J. E., and J. A. Washington, III.
1976.
Comparison of direct and standardized antimicrobial susceptibility testing of positive blood cultures.
Antimicrob. Agents Chemother.
10:211-214[Abstract/Free Full Text].
|
| 10.
|
Kamm, W., and J. Bille.
1985.
Evaluation of the Cobasbact system for rapid antimicrobial susceptibility testing of positive blood culture broths.
Eur. J. Clin. Microbiol.
4:579-582[Medline].
|
| 11.
|
Kiehn, T. E.,
C. Capitolo, and D. Armstrong.
1982.
Comparison of direct and standard microtiter broth dilution susceptibility testing of blood culture isolates.
J. Clin. Microbiol.
16:96-98[Abstract/Free Full Text].
|
| 12.
|
Kluge, R. M.
1975.
Accuracy of Kirby-Bauer susceptibility tests read at 4, 8, and 12 hours of incubation: comparison with readings at 18 to 20 hours.
Antimicrob. Agents Chemother.
8:139-145[Abstract/Free Full Text].
|
| 13.
|
Liberman, D. F., and R. G. Robertson.
1975.
Evaluation of a rapid Bauer-Kirby antibiotic susceptibility testing for bacteria isolated from blood.
Antimicrob. Agents Chemother.
7:250-255[Abstract/Free Full Text].
|
| 14.
|
McGregor, A.,
F. Schio,
S. Beaton,
V. Boulton,
M. Perman, and G. Gilbert.
1995.
The MicroScan WalkAway diagnostic microbiology system an evaluation.
Pathology
27:172-176[Medline].
|
| 15.
|
Mirrett, S.
1994.
Antimicrobial susceptibility testing and blood cultures.
Clin. Lab. Med.
14:171-179[Medline].
|
| 16.
|
Mirrett, S., and L. B. Reller.
1979.
Comparison of direct and standard antimicrobial disk susceptibility testing for bacteria isolated from blood.
J. Clin. Microbiol.
10:482-487[Abstract/Free Full Text].
|
| 17.
|
Moore, D. F.,
S. S. Hamada,
E. Marso, and W. J. Martin.
1981.
Rapid identification and antimicrobial susceptibility testing of gram-negative bacilli from blood cultures by the AutoMicrobic system.
J. Clin. Microbiol.
13:934-939[Abstract/Free Full Text].
|
| 18.
|
National Committee for Clinical Laboratory Standards.
1997.
Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically, 4th ed. Approved standard M7-A4.
National Committee for Clinical Laboratory Standards, Wayne, Pa.
|
| 19.
|
Nolte, F. S.,
P. B. Contestable,
D. Lincalis, and A. Punsalang, Jr.
1986.
Rapid, direct antibiotic susceptibility testing of blood culture isolates using the Abbott Advantage System®.
Am. J. Clin. Pathol.
86:665-669[Medline].
|
| 20.
|
Sahm, D. L.,
S. Boonlayangoor, and J. A. Morello.
1987.
Direct susceptibility testing of blood culture isolates with the AutoMicrobic system (AMS).
Diagn. Microbiol. Infect.
8:1-11.
|
| 21.
|
Trenholme, G. M.,
R. L. Kaplan,
P. H. Karakusis,
T. Stine,
J. Fuhrer,
W. Landan, and S. Levin.
1989.
Clinical impact of rapid identification and susceptibility testing of bacterial blood culture isolates.
J. Clin. Microbiol.
27:1342-1345[Abstract/Free Full Text].
|
| 22.
|
Visser, M. R.,
L. Bogaards,
M. Rozenberg-Arska, and J. Verhoef.
1992.
Comparison of the autoSCAN-W/A and Vitek Automicrobic systems for identification and susceptibility testing of bacteria.
Eur. J. Clin. Microbiol. Infect. Dis.
11:979-984[Medline].
|
| 23.
|
Waites, K. B.,
E. S. Brookings,
S. A. Moser,
M. L. McKinnon, and L. Van Pelt.
1996.
Direct susceptibility testing from positive BacT/Alert® blood culture specimens using MicroScan® overnight and rapid panels, abstr. C-313, p. 56.
In
Abstracts of the 96th General Meeting of the American Society for Microbiology 1996. American Society for Microbiology, Washington, D.C.
|
| 24.
|
Wegner, D. A.,
C. R. Mathis, and T. R. Neblett.
1976.
Direct method to determine the antibiotic susceptibility of rapidly growing blood pathogens.
Antimicrob. Agents Chemother.
9:861-862[Abstract/Free Full Text].
|
| 25.
|
Wu, J. J.,
A. H. Huang,
J. H. Dai, and T. C. Chang.
1997.
Rapid detection of oxacillin-resistant Staphylococcus aureus in blood cultures by an impedance method.
J. Clin. Microbiol.
35:1460-1464[Abstract].
|
Journal of Clinical Microbiology, October 1998, p. 2882-2886, Vol. 36, No. 10
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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Abstract
Introduction
