Comparative evaluation of three chromogenic agars for detection and rapid identification of aerobic Gram-negative bacteria in the normal intestinal microflora

To compare three different chromogenic agars and MacConkey agar for the detection of aerobic Gram-negative bacteria in the normal intestinal microflora and to assess the accuracy of the chromogenic agars for the direct identification of Escherichia coli. A total of 164 Gram-negative clinical isolate...

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Bibliographic Details
Published in:Clinical microbiology and infection 2003-09, Vol.9 (9), p.912-918
Main Authors: Filius, P.M.G., van Netten, D., Roovers, P.J.E., Vulto, A.G., Gyssens, I.C., Verbrugh, H.A., Endtz, H.P.
Format: Article
Language:English
Subjects:
Agar
Bacteriological methods and techniques used in bacteriology
Bacteriology
Biological and medical sciences
Chromogenic Compounds
Chromogenic media
Culture Media
detection
Enterobacter
Escherichia coli
Escherichia coli - growth & development
Escherichia coli - isolation & purification
Escherichia coli Infections - blood
Escherichia coli Infections - microbiology
Feces - microbiology
Fundamental and applied biological sciences. Psychology
Gram-negative bacteria
Gram-Negative Bacteria - growth & development
Gram-Negative Bacteria - isolation & purification
Humans
identification
Intestinal Diseases - diagnosis
Intestinal Diseases - microbiology
Klebsiella
Microbiology
Morganella
normal intestinal microflora
Predictive Value of Tests
Proteus
Pseudomonas
stool specimens
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Summary:To compare three different chromogenic agars and MacConkey agar for the detection of aerobic Gram-negative bacteria in the normal intestinal microflora and to assess the accuracy of the chromogenic agars for the direct identification of Escherichia coli. A total of 164 Gram-negative clinical isolates (E. coli, Proteus, Klebsiella, Enterobacter, Morganella and Pseudomonas species) and 30 stool specimens were inoculated in parallel on four media: Chromagar E. coli/Coliform, Chromogenic urinary tract infection UTI medium, CHROMagar Orientation and MacConkey agar. All colonies that differed by color and/or morphology were selected for further identification by VITEK 1 and/or API 20E from each medium. On E. coli/Coliform agar five out of 32 (16%) E. coli strains failed to produce the color as described by the manufacturer. No remarkable discrepancies were found for the other clinical isolates. There was no significant difference in detection rate (DR) of aerobic Gram-negative bacteria in stool specimens between the different chromogenic agars and MacConkey agar. The overall DR was about 84%, and varied from 100% for monomicrobial specimens to 33% for polymicrobial specimens. The positive predictive values (PPV) for the direct identification of E. coli on Chromagar E. coli/Coliform, Chromogenic UTI medium and CHROMagar Orientation were 1.00, 0.93 and 0.93, respectively. The negative predictive values (NPV) were 0.53, 0.68 and 0.69, respectively. Chromogenic UTI medium and CHROMagar Orientation are the preferred media because of the higher NPV. The high PPV of these agars allows accurate and rapid identification of E. coli.
ISSN:1198-743X
1469-0691
DOI:10.1046/j.1469-0691.2003.00667.x