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editorial
. 1998 May;36(5):1464. doi: 10.1128/jcm.36.5.1464-1464.1998

Evaluation of BBL CHROMagar and CPS ID2 Media for Detection and Presumptive Identification of Urinary Tract Pathogens

Subhash C Arya 1
PMCID: PMC104857  PMID: 9574734

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, Hammann R, Fahr A-M. Evaluation of BBL CHROMagar Orientation medium for detection and presumptive identification of urinary tract pathogens. J Clin Microbiol. 1997;35:2773–2777. doi: 10.1128/jcm.35.11.2773-2777.1997. [DOI] [PMC free article] [PubMed] [Google Scholar]
J Clin Microbiol. 1998 May;36(5):1464.

AUTHORS’ REPLY

Dr A-M Fahr 1,2, Dr R Hammann 1,2

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.

Articles from Journal of Clinical Microbiology are provided here courtesy of American Society for Microbiology (ASM)

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