Journal of Clinical Microbiology, May 1998, p. 1464-1464, Vol. 36, No. 5
0095-1137/98/$00.00+0
LETTERS TO THE EDITOR
Evaluation of BBL CHROMagar and CPS ID2 Media for Detection and
Presumptive Identification of Urinary Tract Pathogens
 |
LETTER |
The microbiological performance of BBL CHROMagar Orientation
medium and CPS ID2 agar was evaluated with 658 clinical urine specimens
from different sources from Heidelberg, Germany. Presumptive pathogen identifications were based on the activities of different bacterial enzymes, which were monitored by color changes in
chromogens incorporated in the BBL CHROMagar and ID2 media
(1). Chromogenic culture media emerged as excellent and
time-saving devices for the detection and quantification of patients'
urinary tract pathogens. However, it would be pertinent to study the
inhibition by different antibacterial substances on the various
bacteria present in a urinary specimen.
In the present series (1), antibacterial activity was
reported in 152 of the 658 urine specimens. Of the 152 samples, 78 had
>105 CFU of bacteria/ml and 34 had <105 CFU
of bacteria/ml, while there was no growth in 40 samples. Before the
switch to exclusive use of chromogenic culture media for diagnosis of
urinary tract infection is made, the inhibition by various
antibacterial agents in clinical specimens on the bacterial enzymes
responsible for color changes in chromogenic media should be
investigated fully. This could be done through characterization of the
antibacterial substance in the patient's urine and the antibiotic
susceptibility profile of the pathogenic or even saprophytic bacteria
in the specimen. The two should be correlated carefully lest a partial
or total inactivation of bacterial enzymes by the antibacterial
substance, though not necessarily an antibiotic, be associated with an
erroneous result with BBL CHROMagar or CPD 1D2 medium. Undoubtedly, an
identical approach with nonurine specimens (1) would
eliminate any false-negative reports attributable to the inhibition of
enzymes by an antibacterial substance in the pathological
specimens.
| |
REFERENCE |
| 1.
|
Hengstler, K. A.,
R. Hammann, and A.-M. Fahr.
1997.
Evaluation of BBL CHROMagar Orientation medium for detection and presumptive identification of urinary tract pathogens.
J. Clin. Microbiol.
35:2773-2777[Abstract].
|
| | | | |
Subhash C. Arya
Centre for Logistical Research and Innovation
M-122 (of Part 2), Greater Kailash-II
New Delhi 110048, India
|
| |
AUTHORS' REPLY |
We appreciate the comment of Dr. Arya on our paper and his concern
about the influence of the antimicrobial agents used for the therapy of
the urinary tract infections on the inhibition of bacterial enzymes,
which can possibly result in an incorrect identification when
chromogenic substrates are used. However, we would like to add the
following comments.
First, in about 23% of the specimens investigated, the identification
with the chromogenic substrates was performed not in the urine
specimens which contained the antimicrobial substances but on culture
media which were free of antimicrobials. Even if the isolates and their
enzymatic activities had been influenced by the agents present in the
urine, they had the chance to recover on the culture media.
Second, the isolation of bacteria from clinical specimens is generally
performed by culturing on media which are nonselective or selective
(possibly by antimicrobial agents) and which contain substrates and
indicators that detect a certain biochemical activity of the
isolate(s). The biochemical activities exhibited on differential media,
like those exhibited following inoculation of an identification system,
are used to identify the isolate. Nearly all of the tests used for the
classical identification of bacteria are based on bacterial enzymes.
Over many years, biochemical tests have been successfully used to
identify microorganisms, whether the isolates were derived from
specimens containing antimicrobial substances or not. If Dr. Arya
doubts the reliability of the identification on chromogenic media of
microorganisms isolated from specimens containing antimicrobials, he
must likewise doubt the reliability of the widely applied technique of
using biochemical tests for their identification in general.
Third, if the production of bacterial enzymes had been affected by the
antimicrobial agents, we would have recovered a much higher rate of
false-negative Escherichia coli isolates, enterococci, or
other isolates not exhibiting the expected colony color on the
chromogenic media, as all of the unstained organisms from the
chromogenic media had been subjected to a full biochemical identification.
For a routine diagnostic laboratory, it is usually impossible to obtain
data on the type of antimicrobial used for the treatment of a patient,
and many different compounds with several different mechanisms of
target action on the bacterial cell are used. We feel that one of the
results of our investigation was confirmation that the chromogenic
media tested worked well with urine samples of both pretreated and
untreated patients.
| | | | |
Dr. A.-M. Fahr
Laboratory Group
Department of Microbiology
Im Breitspiel 15
D-69126 Heidelberg, Germany
|
| | | | |
Dr. R. Hammann
Becton Dickinson Microbiology Systems Europe
R&D Microbiology
Tullastrasse 8-12
D-69126 Heidelberg, Germany
|
Journal of Clinical Microbiology, May 1998, p. 1464-1464, Vol. 36, No. 5
0095-1137/98/$00.00+0
Previous Article | Next Article 
Top
Letter
References
