Evaluation of the Minitek System for Identification of Enterobacteriaceae

Clinical isolates (869) and stock cultures (35) of Enterobacteriaceae were tested in parallel with the Minitek and conventional systems. The Minitek correctly identified 822 of 904 cultures. When a deoxyribonuclease plate was inoculated along with the Minitek, it was possible to speciate Enterobacteriaceae within 24 h. False-positive hydrogen sulfide reactions were the major fault with this system. Reactions were clear-cut and easy for technologists to read.     

Identification of Enterobacteriaceae with the Minitek system

A total of 417 strains (361 Enterobacteriaceae, 56 Vibrionaceae) was examined in all the available Minitek system tests. The results were processed through four successive identification schemes devised by the manufacturer and the proportion of strains correctly identified, not identified or incorrectly identified determined for each scheme. From the results, a probability matrix was constructed incorporating all 35 Minitek tests. Test results for each strain were then processed through this matrix to determine its success in identification. From the matrix the order of separating value of the tests was determined. Forty-three of the strains were each tested three times to assess the level of test reproducibility; the corrected error rate was 0.85%.     

Identification of Enterobacteriaceae with the Minitek system

A total of 417 strains (361 Enterobacteriaceae, 56 Vibrionaceae) was examined in all the available Minitek system tests. The results were processed through four successive identification schemes devised by the manufacturer and the proportion of strains correctly identified, not identified or incorrectly identified determined for each scheme. From the results, a probability matrix was constructed incorporating all 35 Minitek tests. Test results for each strain were then processed through this matrix to determine its success in identification. From the matrix the order of separating value of the tests was determined. Forty-three of the strains were each tested three times to assess the level of test reproducibility; the corrected error rate was 0.85%.     

Evaluation of the Auxotab Enteric 1 System for Identification of Enterobacteriaceae

An evaluation of the accuracy and convenience of the Auxotab Enteric 1 System for identification of Enterobacteriaceae was performed with 160 bacteria. Identification at the species level was correct in 134 (83.8%) instances and at the generic level in 144 (90%) instances. Sixty strains failed to achieve the minimal concentration of organisms required to complete the identification process within 7 hr. The system was judged to be laborious and to present a potential hazard to those working with it.     

Evaluation of the Modified R/B System for Identification of Enterobacteriaceae

In comparison with conventional procedures, a modified R/B Enteric Differential System permitted more accurate identification of enteric bacteria than did the original R/B system.     

Evaluation of Accuracy of Multitest Micromethod System for Identification of Enterobacteriaceae

The Analytab system of 20 biochemical tests for identification of Enterobacteriaceae was evaluated in parallel with conventional tests on 128 Enterobacteriaceae, 5 Aeromonas, and 1 Yersinia enterocolitica. The results of tests for H(2)S and indole production, citrate utilization, lysine and ornithine decarboxylase, arginine dihydrolase, nitrate reduction, beta-galactosidase, and fermentation of arabinose, rhamnose, mannitol, and glucose showed almost complete agreement between the two systems. Eighty-eight per cent of Enterobacteriaceae were correctly speciated with the Analytab system; on repeat testing with heavier inocula of organisms failing to ferment glucose initially, the proportion of Enterobacteriaceae correctly speciated became 93%.     

Evaluation of the Enterotube System for Identification of Members of the Family Enterobacteriaceae

The Enterotube system was evaluated, in parallel with conventional bacteriological procedures for the identification of members of the family Enterobacteriaceae, by using bacterial strains from a variety of clinical specimens and from stock cultures. Excellent agreement between the two test systems was obtained with the following reactions: hydrogen sulfide, indole, Simmons' citrate, glucose, and lactose. Agreement was not as good (<85%) with the urea, phenylalanine deaminase, and dulcitol reactions. The Enterotube lysine decarboxylase test was unsatisfactory. The Enterotube method will correctly identify strains of the family Enterobacteriaceae approximately 50% of the time; if identification only as Klebsiella-Enterobacter-Serratia group is needed, the method will be correct 85% of the time. On the basis of this evaluation, the Enterotube system appears to be both simple and rapid for the presumptive identification of these bacteria. Because of the limited usefulness of the lysine decarboxylase test, the results obtained by this test system are less reliable than those obtained by conventional methods.     

Evaluation of Modified R-B System for Identification of Members of the Family Enterobacteriaceae

In a paired, double-blind study, the modified ("Beckford tube") R-B system was compared with conventional bacteriological procedures for the identification of members of the family Enterobacteriaceae from clinical isolates and stock cultures. The tests in the R-B system yielding positive reactions comparable to those predicted by Ewing's taxonomic classification of Enterobacteriaceae were production of hydrogen sulfide and presence of lysine and ornithine decarboxylasè activities. The test reactions in the R-B system found to be comparable to those in the conventional method were fermentation of glucose, hydrogen sulfide production, and lysine and ornithine decarboxylase activities. The production of gas from glucose was positive in the R-B system more often than in the conventional method; however, the motility test and the production of indole were positive less often in the R-B system. Adequate preliminary identification of the Enterobacteriaceae with the R-B system is enhanced if Simmons' citrate and Christensen's urea tests are used concomitantly. These findings emphasize the manufacturer's instructions that, in interpretation of results, colonial morphology and biochemical reactions must be used concurrently to make an accurate identification.     

Evaluation of the Minitek system for characterization of Bacillus species

Minitek (BBL Microbiology Systems, Cockeysville, Md.) substrate disks were evaluated as alternatives to conventional tests for the characterization of Bacillus species. Results were compared for 10 reference isolates and 87 isolates from food sources. The overall agreement of results between the Minitek and conventional tests was 92% for reference strains and 86% for food isolates.     

Evaluation of the Improved Auxotab 1 System for Identifying Enterobacteriaceae

The improved Auxotab Enteric 1 System is more accurate in identifying Enterobacteriaceae than is the original product, and results correlate better with those obtained with conventional tests.     

Evaluation of the Minitek system for characterization of Bacillus species.

Minitek (BBL Microbiology Systems, Cockeysville, Md.) substrate disks were evaluated as alternatives to conventional tests for the characterization of Bacillus species. Results were compared for 10 reference isolates and 87 isolates from food sources. The overall agreement of results between the Minitek and conventional tests was 92% for reference strains and 86% for food isolates.     

R/B Enteric Differential System for Identification of Enterobacteriaceae

The R/B Enteric Differential System for identifying enteric bacteria has been evaluated with 451 "unknown" cultures from the stock culture collection of the Center for Disease Control. An average of 89.6% of these cultures were correctly identified by the R/B system, when used as recommended by the manufacturer but without the assistance of serology. This percentage ranged, however, from 47% for Klebsiella to 100% for Serratia and Providencia. Of 11 groups or genera of Enterobacteriaceae tested, only three (Enterobacter, Serratia, and Providencia) were identified with 95% or better accuracy. Four groups (Arizona, Citrobacter, Escherichia, and Salmonella) attained 90 to 95% accuracy of identification, and three groups (Edwardsiella, Proteus, and Shigella) scored between 85 and 90% accuracy. We recommend the R/B system as a screening device which is reasonably successful in grouping bacteria but not as a substitute for more exacting conventional procedures.     

API System: a Multitube Micromethod for Identification of Enterobacteriaceae

The API system for identification of Enterobacteriaceae was evaluated with 366 cultures. Overall accuracy of identification was 96.4%; of the 13 cultures misidentified, 7 were atypical strains.     

Identification of Members of the Family Enterobacteriaceae by the R-B System

The R-B system was evaluated in parallel with conventional bacteriological procedures for the identification of members of the family Enterobacteriaceae by using bacterial strains from a variety of clinical specimens and from stock cultures. The R-B tests found to be reliable were, in decreasing order, the reactions for phenylalanine deaminase, hydrogen sulfide, and indole, the production of gas from glucose, and the decarboxylation of ornithine. The reactions in the R-B system found to be unreliable were motility, the decarboxylation of lysine, and the fermentation of both glucose and lactose. In addition, the reactions of the R-B system were more difficult to read and interpret than those of the conventional system. On the basis of this evaluation, it was concluded that the R-B system is not an acceptable alternative to the conventional methods in the identification of the Enterobacteriaceae.     

Numerical Diagnostic Key for the Identification of Enterobacteriaceae

A numerical diagnostic key for enteric organisms is described which permits the identification of typical strains and of biochemical variants with high accuracy. Unknown strains are inoculated into a basic set of five media which permit the testing of eight biochemical reactions. The positive reactions are assigned points, and the score of a strain is added up, after which the identification of the strain is obtained from a table. In many instances, the final identification is obtained with this set of biochemical tests; and, in other instances, a small number of additional tests are required to distinguish between organisms giving the same score in the basic set of biochemical tests. The key permits an accurate, rapid, and economical differentiation of the typical and the more common atypical biotypes of enteric organisms in the clinical laboratory.     

Rapid Ornithine Decarboxylase Test for the Identification of Enterobacteriaceae

Conventional methods for detecting ornithine decarboxylase activity require an extended period of incubation. However, with a few simple modifications, accurate results were obtained within a few hours rather than several days. The broth medium was modified, primarily by omitting glucose and by decreasing the pH to 5.5. A 1-ml amount of this broth was inoculated with one colony and then overlaid with sterile mineral oil. Within 2 to 4 hr, the pH increased if ornithine was decarboxylated, thus changing the color of the internal pH indicator to a dark purple. If the amino acid was not decarboxylated, the pH decreased to pH 5.0 to 5.2, enough to give a definite yellow color. With 347 selected clinical isolates, the rapid test gave results identical to those obtained in 1 to 4 days with Moeller's decarboxylase medium. Less reliable results were obtained with Difco's decarboxylase medium with 0.3% agar which was stabinoculated and read after 18 to 24 hr without a mineral oil seal. The rapid ornithine decarboxylase test represents a simple, accurate technique which is well suited for the clinical microbiology laboratory.     

Efficiency of a Multitest System (Enterotube) for Rapid Identification of Enterobacteriaceae

Enterotube, a multiple-test system which combines nine biochemical tests useful in the identification of members of the family Enterobacteriaceae, was tested and compared with the PathoTec test system in the identification of gram-negative bacilli isolated from clinical specimens. It was found that both the Enterotube and the PathoTec systems rapidly and accurately defined the position of the organisms in the major groups of the family Enterobacteriaceae. Discrepancies were noted between the results of citrate tests on Simmons' citrate-agar and in the Enterotube, as well as between Simmons' citrate-agar and the PathoTec citrate test. It was concluded that the Enterotube system provides a simple, reliable, and rapid method for the presumptive identification of Enterobacteriaceae. The major advantage of the Enterotube is that all tests are done simultaneously by inoculation from a single isolated colony.     

Microfermentation Series for Identification of Single Colonies of Enterobacteriaceae

Microfermentation tests for members of the family Enterobacteriaceae were devised by using agar solutions in disposable, multi-welled, plastic trays. The tests could be made directly from isolated colonies picked from agar plates and represented a considerable saving in time, labor, and materials over the conventional methods. Tests were formulated for determining carbohydrate fermentations, citrate utilization, motility, amino acid decarboxylation, and production of H(2)S, indole, urease, and acetyl-methyl-carbinol.     

Identification of Enterobacteriaceae in the Clinical Microbiology Laboratory

A total of 5,137 enterobacterial clinical isolates were examined with three series of biochemical tests. The data were analyzed with respect to the use of economical and practical procedures for the accurate identification of lactose-fermenting and -nonfermenting Enterobacteriaceae within 24 hr after isolation.