agar and indole

Escherichia coli is the most common gram-negative microbe isolated and identified in clinical microbiology laboratories. It can be identified within 1 h by oxidase, indole, lactose, and beta-glucuronidase tests. The oxidase and indole tests are performed as spot tests, and lactose fermentation is read directly from MacConkey agar. It was found that 4-methylumbelliferyl-beta-D-glucuronide could be incorporated directly into a modified MacConkey agar to directly detect the presence of beta-glucuronidase. Other characteristics of MacConkey agar were not affected. The incorporation of 4-methylumbelliferyl-beta-D-glucuronide into modified agar obviated the need for manufacture, quality control, and incubation of reagent-containing test tubes. The time needed to identify E. coli strains was reduced from 1 h to 5 min, and the ability to detect this species in mixed specimens was also enhanced.

Topics: Agar; Culture Media; Escherichia coli; Fermentation; Fluorescence; Glucuronates; Glucuronidase; Hymecromone; Indoles; Lactose; Oxidoreductases; Time Factors

The use of primary isolation plate colonial morphologic criteria (CMC) of a flat, nonmucoid, lactose-fermenting, gram-negative rod on MacConkey agar and the spot indole (SI) test from the sheep blood agar plate was evaluated as a means for identification of Escherichia coli in comparison to kit (Micro-ID, API-20E) and conventional biochemical testing. In this preliminary phase of comparison of accuracy, 427 isolates of E. coli (69.8%) from a total of 612 isolates of lactose-fermenting gram-negative rods were evaluated. Of these E. coli isolates, 357 (83.6%) fit the CMC and were SI positive; 3 (less than 1% error rate) were not E. coli. In the second phase of the evaluation, using CMC and SI alone as a means for identification of E. coli, 472 (57.6%) E. coli isolates from a total of 820 Enterobacteriaceae isolates were assessed. Of these E. coli isolates, 326 could be identified using only CMC and SI (69.1% of the E. coli isolates and 39.8% of all Enterobacteriaceae isolates); 146 (30.9%) required additional biochemical testing because of atypical colonial morphology, because of the investigator's inability to differentiate colony types on both media or lack of isolated colonies on either of the two required media, or because as isolates from sterile body sites they were processed directly to Micro-ID kits. A minimum of 40% savings on Enterobacteriaceae identification schemes without compromising accuracy was calculated. As of November 1983, a direct (labor and materials) cost savings of approximately +200.80 per 100 Enterobacteriaceae identifications was projected.

Topics: Agar; Bacteriological Techniques; Cost-Benefit Analysis; Enterobacteriaceae; Escherichia coli; Indoles; Reagent Kits, Diagnostic

The biochemical characteristics of six strains of Klebsiella pneumoniae that produced H2S in TSI slants are described. All were biotypical except for the consistent characteristic of indole production. It is suggested that the qualities of H2S and indole production are linked biochemical features acquired by episomal transfer. The attention of bacteriology laboratory workers is directed to these strains, which are easily distinguished biochemically from other H2S-producing organisms by their otherwise biotypical pattern.

Topics: Agar; Animals; Biomarkers; Culture Media; Humans; Hydrogen Sulfide; Indoles; Iron; Klebsiella Infections; Klebsiella pneumoniae