Spot Indole Test Research Articles

Epidemiology of Klebsiella oxytoca-Associated Diarrhea Detected by Simmons Citrate Agar Supplemented with Inositol, Tryptophan, and Bile Salts

We studied the clinical and epidemiological characteristics of Klebsiella oxytoca-associated diarrhea in hospitalized patients in Hong Kong. Between 1 November 2009 and 30 April 2011, all inositol-fermenting colonies found on Simmons citrate agar supplemented with inositol, tryptophan, and bile salts (SCITB agar) used for the culturing of diarrheal stool samples were screened by a spot indole test for K. oxytoca. The overall sensitivity of SCITB agar plus the spot indole test (93.3%) for the detection of K. oxytoca in stool samples was superior to that of MacConkey agar (63.3%), while the specificities were 100% and 60.4%, respectively. The former achieved a 23-fold reduction in the workload and cost of subsequent standard biochemical identifications. Cytotoxin production and the clonality of K. oxytoca were determined by a cell culture cytotoxicity neutralization assay using HEp-2 cells and pulsed-field gel electrophoresis (PFGE), respectively. Of 5,581 stool samples from 3,537 patients, K. oxytoca was cultured from 117/5,581 (2.1%) stool samples from 104/3,537 (2.9%) patients. Seventy-six of 104 (73.1%) patients with K. oxytoca had no copathogens in their diarrheal stool samples. Twenty-four (31.6%) of 76 patients carried cytotoxin-producing strains, which were significantly associated with antibiotic therapy after hospital admission (50% versus 21.2%; P = 0.01). Health care-associated diarrhea was found in 44 (42%) of 104 patients with K. oxytoca, but there was no epidemiological linkage suggestive of a nosocomial outbreak, and PFGE showed a diverse pattern. None of the patients with cytotoxin-producing K. oxytoca developed antibiotic-associated hemorrhagic colitis, suggesting that K. oxytoca can cause a mild disease manifesting as uncomplicated antibiotic-associated diarrhea with winter seasonality.

Evaluation of a new chromogenic medium, Uriselect 4, for the isolation and identification of urinary tract pathogens

Aims: To compare the performance of a new chromogenic medium, Uriselect 4, with cystine lactose electrolyte deficient (CLED) agar and an established chromogenic agar, CPS ID 2 medium, for detection...

Emended descriptions of indole negative and indole positive isolates of Brachyspira (Serpulina) hyodysenteriae

Two type/reference strains of Brachyspira (B.) hyodysenteriae, 14 Belgian and German indole negative, and 14 Belgian, German and Swedish indole positive field isolates of strongly β-haemolytic intestinal spirochaetes were compared by pulsed-field gel electrophoresis (PFGE) patterns, biochemical reaction patterns, 16S rDNA sequences and MIC determinations of six antibacterial substances. Three tests for indole production, including a spot indole test, were compared with congruent results. All field isolates were classified as B. hyodysenteriae due to a high genetic and phenotypic similarity with the type strains. The Belgian and German indole negative isolates had identical and unique PFGE patterns for the tested restriction enzymes MluI and SalI, as well as identical 16S rDNA sequences, and they could not be differentiated by any of the methods used. Seven unique PFGE patterns were achieved from the 14 indole positive field isolates. The patterns were identical and unique for epidemiologically related isolates. Type/reference strains and isolates without known relation to other tested isolates showed unique banding patterns. The MICs of tylosin, tiamulin, erythromycin, clindamycin, carbadox and virginiamycin were determined in broth for all isolates. In contrast to Belgian and German isolates, the majority of the Swedish field isolates were susceptible to tylosin, erythromycin and clindamycin. Probable pathways of infection for some of the Swedish isolates were determined. The PFGE patterns of epidemic clones of B. hyodysenteriae remained stable for a period of up to 8 years. In vivo development of resistance to macrolide and lincosamide antibiotics due to use of tylosin was clearly indicated for two epidemic clones.

Evaluation of the Cobas-Bact® System for Direct and Rapid Identification and Antimicrobial Susceptibility Testing of Enterobacteriaceae from Positive Urine Specimens

A direct antimicrobial susceptibility test and a direct identification of Gram-stained urine specimens positive for Enterobacteriaceae using a new instrument (Cobas-Bact®) were compared by means of the conventional Kirby-Bauer agar diffusion disk method and the spot indole test, an in-house set of identification tests or API 20E. Bacteria from 191 cases of monomicrobial bacteriuria due to members of the family Enterobacteriaceae were tested. Direct susceptibility testing was performed in 180 cases (94%), providing 1649 antibiotic-microorganism combinations. A complete agreement was reached in 82% and essential agreement in 92% of cases. Minor discrepancies were found in 163 (9.9%) major ones in 125 (7.6%) and very major ones in 10 (0.6%) of examinations. 72% of all minor and 71 of all major discrepancies were caused by two antibiotics: cephalothin and nitrofurantoin. Of the very major discrepancies, 50% were due to amoxicillin. Of 171 direct identifications obtained, 130 (76%) were “2high-confidence” correct identifications (percentage of likelihood p ⩾ 80%), 25 (14.6%) “low-confidence” identifications (percentage of likelihood p ⩾ 80%) and 16 (9.4%) misidentifications. On the whole, this direct and rapid Cobas-Bact® identification and susceptibility testing procedure provided satisfying information within 5–6 h after collection of urine specimens positive for members of the Enterobacteriaceae family.

Untersuchungen zu methodischen problemen beim nachweis der indolbildung durch anaerobe krankheitserreger

The demonstration of indole formation is of great value for the identification of pathogenic anaerobes. A reduction of the pH to values below the critical range of 5.1–5.3 in complex media 5.5 in simple testing substrates, respectively, which is caused by the presence of fermentable carbohydrates and will result in false-negative reactions. For this reason, the indol test should be performed with an adequate buffer capacity and an addition of fermentable carbohydrates should be avoided. Strains showing a false-negative reaction in the spot indole test can be reliably accounted for by means of the rapid test in buffered tryptophan solution described here without having to use additional anaerobic culture methods.

Comparison of Methods for Identification of Hemophilus influenzae

Several methods for identification of Hemophilus influenzae—the satellite test using a strain of Staphylococcus aureus or X, V, and XV factor strips, the Hemophilus identification quadrant plate, the spot indole test, and the 8-amino levulinic acid (ALA) test for porphyrin synthesis using laboratory prepared reagent or a commercial ALA disk—were compared for sensitivity, specificity, ease of performance, and cost. The ALA test using a laboratoryprepared reagent on a filter paper strip was highly sensitive and specific as well as being easy to perform and inexpensive.

The spot indole test for identification of swarming Proteus.

The authors evaluated the use of the spot indole test for rapid speciation of swarming Proteus from the primary isolation plate. One hundred seventy-two consecutive isolates of swarming Proteus were studied, 163 Proteus mirabilis and nine Proteus vulgaris. One hundred fifty-six isolates (95.7%) of Proteus mirabilis gave a negative spot indole. Seven (4.3%) gave a positive spot indole test, but all seven isolates were from cultures in which other indole-producing organisms also were present. If only isolates representing single gram-negative strains in the specimens were tested, the predictive value was greater than 99%. Eight of the nine (88.9%) Proteus vulgaris isolates gave a positive spot indole test; one (11.1%) gave a negative result. This isolate also failed to produce indole by conventional methods but was ornithine decarboxylase negative, and additional biochemical testing was consistent with the Proteus vulgaris identification. All Proteus vulgaris isolates were resistant to ampicillin, and 94.2% of the Proteus mirabilis tested were ampicillin susceptible. The spot indole test is a rapid, accurate, simple, and cost-effective means of speciating swarming Proteus strains isolated as the only gram-negative bacilli in a specimen. The spot indole test should be used in conjunction with an ampicillin susceptibility test result or other confirmatory test information if other gram-negative bacilli are present in the culture.

Use of and cost savings with morphologic criteria and the spot indole test as a routine means of identification of Escherichia coli

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 (<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.

Development and evaluation of a miniaturised method as an aid to the identification of clinically important anaerobic bacteria.

A miniaturised method for the identification of anaerobic bacteria is described which employs microtitre fermentation tests, a spot indole test and a nitrate reduction disc test. The results obtained are directly comparable with those produced by a standard conventional method in use at present.

An evaluation of the practicality of the spot-indole test for the identification of Escherichia coli in the clinical microbiology laboratory.

Colony morphology and the spot-indole test were evaluated to assess the practicality of the rapid identification of Escherichia coli isolates directly from primary isolation plates. One hundred ninety-one lactose-fermenting, gram-negative bacilli were identified by standard testing procedures (either API-20E, Micro-ID, or a 5-test biochemical battery). These isolates also were tested with the spot-indole test, using either a 1% or 5% p-dimethylaminobenzaldehyde or 1% p-dimethylaminocinnamaldehyde reagent. Of the total 191 E. coli isolated, 128 (67.0%) were single-colony types on the primary plates, and 112 (58.6%) met the morphologic criteria and were positive and spot-indole testing. Of these 112, 111 (99.1%) were identified accurately as E. coli by the morphologic criteria/spot-indole approach. This method can be recommended as a practical diagnostic aid in the clinical microbiology laboratory as it allows significant cost and time savings for the majority of the most frequently isolated gram-negative bacilli.

Simplified scheme for identification of prompt lactose-fermenting members of the Enterobacteriaceae.

A brief, simplified scheme involving the spot indole test and colonial morphology was evaluated for genus level identification of prompt lactose-fermenting (PLF) members of the Enterobacteriaceae. One hundred and ninety-four consecutive, clinically important PLF gram-negative rods isolated in a clinical microbiology laboratory were identified by this simplified scheme, as well as by standard biochemical tests, and the API 20E (Analytab Products, Inc., Plainview, N.Y.) system. In the simplified scheme a flat, spot indole-positive colony was identified as Escherichia coli. Spot indole-negative organisms forming nucoid colonies were identified as Klebsiella sp. or Enterobacter sp. on the basis of semisolid motility and ornithine decarboxylase tests. Approximately 94% of the study isolates followed reactions typical for E. coli, Klebsiella sp., and Enterobacter sp. as defined by this simplified scheme. When compared with the standard and Analytab Products Inc. identifications, the overall accuracy was 97.4%. The accuracy of identification of E. coli, Klebsiella sp., and Enterobacter sp. was 98.1%, 95.6%, and 87.5%, respectively. This simplified scheme is recommended for identification of selected PLF isolates in the clinical microbiology laboratory.