Comparison of the API rapid E four-hour system with the API 20E overnight system for the identification of routine clinical isolates of the family Enterobacteriaceae.

Four hundred forty-one clinical isolates of the family Enterobacteriaceae were identified in parallel by using the API Rapid E 4-h and the API 20E overnight procedures (Analytab Products, Plainview, N.Y.). The results obtained by using the API Rapid E were compared with those obtained by using the API 20E. Discrepancies were resolved by using standard biochemicals. The API 20E identified 98.9% (436 of 441) of the isolates without the use of additional biochemicals and was found to be correct in each case of a discrepancy among the 436 isolates. The API Rapid E gave the same identification as the API 20E for 94.0% (410 of 436) of the isolates, misidentified 3.0% (13 of 436), and gave a correct but low-selectivity answer for the remaining 3.0% (13 of 436). The API Rapid E is a suitable alternative for the rapid identification of the Enterobacteriaceae.     

Feasibility of same-day identification of members of the family Vibrionaceae by the API 20E system.

Sixty isolates, comprising nine species of the family Vibrionaceae, were tested with the API 20E 5-h same-day procedure (Analytab Products, Plainview, N.Y.). Included were 27 Aeromonas hydrophila isolates, 10 Aeromonas sobria isolates, 7 Aeromonas caviae isolates, 3 Plesiomonas shigelloides isolates, 3 Vibrio alginolyticus isolates, 3 Vibrio cholerae isolates, 1 Vibrio fluvialis isolate, 5 Vibrio parahaemolyticus isolates, and 1 Vibrio vulnificus isolate. The 5-h profile numbers were specific for the five Vibrio species and the Plesiomonas isolates. The three Aeromonas species shared seven 5-h profile numbers. Of the 63 5-h profile numbers generated by testing each isolate twice, 22 were identical to those found in the overnight analytical profile index. Of these, 20 were correct identifications, and two were incorrect. The remaining 41 5-h profile numbers were not found in the overnight analytical profile index. Because the 5-h analytical profile index does not contain any oxidase-positive organisms, the oxidase value was subtracted from the 63 5-h profile numbers to determine whether misidentifications could occur if the oxidase test was either not performed or not performed correctly. Only five of these factored profile numbers resulted in a possible misidentification. It is feasible, within limitations, to use the 5-h API 20E same-day procedure to identify the more commonly occurring members of the Vibrionaceae. The manufacturer should develop a data base for this purpose.     

Four hour identification of Enterobacteriaceae with the API Rapid 20E and Micro-ID systems.

One hundred strains of Enterobacteriaceae were examined in parallel with the API Rapid 20E and Micro-ID commercial four hour identification systems. With the API Rapid 20E system 78% of the strains were correctly identified, 15% were not identified, and 7% were misidentified. The respective figures with the Micro-ID system were 74%, 11%, and 15%.     

Reevaluation of the API 20E identification system versus conventional biochemicals for identification of members of the family Enterobacteriaceae: a new look at an old product.

The API 20E bacterial identification system has been used for 19 years, often as the standard with which other identification systems are compared. Because the accuracy of this system compared with conventional biochemical tests has not been determined in many years, we evaluated the API 20E linear strip by using 291 typical and atypical strains of the family Enterobacteriaceae taken from a culture collection. At 24 h, the API 20E correctly identified by genus and species 229 of 291 (78.7%) of the strains, using Salmonella and Shigella serotyping where indicated. At 48 h, 95.2% were correctly identified by using additional biochemical tests as recommended by the manufacturer. The API 20E misidentified eight (2.7%) strains; these strains were not limited to any particular genus. When 81 of these Enterobacteriaceae strains were arranged into a weighted assortment correlating to the frequency with which they might be found in a clinical laboratory, the API 20E correctly identified 71 (87.7%) at 24 h and 78 (96.3%) at 48 h. This evaluation concluded that the accuracy of the identification of Enterobacteriaceae strains at 24 h (78.7%) may be significantly lower than that of earlier evaluations. However, there is no significant difference in the ability of the API 20E to correctly identify "challenge" type organisms (229 of 291) versus routine hospital isolates (71 of 81) (P greater than 0.05), but the system is not as accurate as the conventional biochemical method of identification.     

Comparison of micro-ID and API 20E in rapid identification of Enterobacteriaceae.

The effectiveness of Micro-ID and API 20E as same-day identification systems for Enterobacteriaceae was evaluated in comparison with conventional identification by using 315 clinical isolates and 90 stock strains. The API 20E system was heavily inoculated according to manufacturer's recommendations for same-day identification. We found that 83 and 81% of isolates provided adequate inocula for Micro-ID and API 20E, respectively, and purity of the heavy inocula was not a problem with either system. Overall agreement with conventional identification at genus and species levels was 93.5% with Micro-ID and 90.2% with API 20E. However, when Klebsiella pneumoniae and K. oxytoca were considered as a single species and Proteus morganii was equated with Morganella morganii, agreement was 95.8 and 90.5%, respectively. Only 83.% of isolates were identified on the day of inoculation by API 20E, in contrast to 94.3% with Micro-ID. The remaining isolates required supplementary overnight testing. Provisional (low selectivity) determinations were constant with conventional identification with 49.3% of isolates with API 20E and 82.6% with Micro-ID. Telephone consultations with the manufacturers to resolve unprinted octal codes required a maximum of 15 min with Micro-ID and from 2 to greater than 48 h with API 20E.     

Evaluation of the DMS Rapid E system for identification of clinical isolates of the family Enterobacteriaceae.

A total of 387 unique clinical isolates of the family Enterobacteriaceae were examined with the new DMS Rapid E gram-negative identification system (DMS Laboratories, Inc., Flemington, N.J.) and the API 20E procedure (Analytab Products, Plainview, N.Y.). Altogether, 376 strains (97.2%) were correctly identified to species level within 4 h with the DMS Rapid E system; 366 strains (94.6%) were correctly identified with the API 20E after overnight incubation.     

Evaluation of the four-hour rapid 20E system for identification of members of the family Enterobacteriaceae

A study was conducted to compare the API Rapid 20E 4-h system (API System S.A., France; commercially available in the U.S.A. under the name DMS Rapid E System; DMS Laboratories, Darts Mill, Flemington, N.J.), the API 20E 18- to 24-h system (Analytab Products, Plainview, N.Y.), and a conventional media system to measure the ability of each to identify members of the family Enterobacteriaceae. Comparison tables rather than simple percentage agreement tables were generated to define the particular strengths and weaknesses of each system and to allow the laboratory to best use the data. The Rapid 20E compared quite favorably with conventional media. It yielded correct identifications with 95.9% of the isolates tested (API 20E, 98% identification rate). In 2.5% of the isolates, the Rapid 20E gave only genus identifications, and in 1.4% the organisms did not correspond to any key in the code book and could not be identified by the manufacturer's computer service. The ease of inoculation and the 4-h capability make the Rapid 20E system an extremely attractive development in the field of bacterial identification.     

Evaluation of the Quantum II and Rapid E identification systems.

A total of 492 clinical isolates from the family Enterobacteriaceae were tested in the API 20E, Rapid E, and Quantum II identification systems. Discrepant identifications among these three systems were resolved by repeat testing in the identification systems or use of conventional biochemical tests. Of these isolates, 94.1% were correctly identified with the API 20E and Rapid E systems, and 97.0% were correctly identified with the Quantum II system. An additional 48 non-Enterobacteriaceae isolates were tested with the Quantum II system, and 83.3% were correctly identified. The majority of incorrect identifications with the Rapid E and Quantum II systems were caused by a single aberrant biochemical reaction. Reproducibility of the biochemical reactions obtained with these two systems was evaluated by testing 40 organisms in triplicate. Identical biocodes for all three tests were obtained for 10 organisms with the Quantum II system and for 19 organisms with the Rapid E system. Reproducibility of the Quantum II test results was improved with a subsequent modification of the photometer of this system. Both the Rapid E and Quantum II systems were inexpensive and were technically easy to inoculate and interpret.     

Identification of clinically isolated vancomycin-resistant enterococci: comparison of API and BBL Crystal systems.

Twenty-eight phenotypically separate strains of clinically isolated vancomycin-resistant enterococci have been investigated with two API identification kit systems (20 Strep and Rapid ID 32 Strep) and two BBL Crystal kits (Gram Positive and Rapid Gram Positive). All strains were identified as Enterococcus faecium by a reference laboratory. The Rapid ID 32 kit positively identified 15 of 28 strains (54%), but only two (7%) were identified correctly: 11 were identified as 'doubtful' or 'to genus level' and two gave 'unacceptable' profiles. The API 20 Strep kit identified 27 strains (96%), but only 16 (57%) were identified correctly as E. faecium. The Rapid ID 32 kit erred by either positively misidentifying vancomycin-resistant E. faecium as E. casseliflavus or E. gallinarum, or indicated that this was the most likely identification, while the API 20 Strep kit more commonly produced a misidentification as E. casseliflavus. The Crystal Gram Positive and Rapid Gram Positive kits correctly identified 26 (93%) and 27 (96%) of the strains, respectively.     

Evaluation of the Phoenix 100 ID/AST system and NID panel for identification of Enterobacteriaceae, Vibrionaceae, and commonly isolated nonenteric gram-negative bacilli

The Phoenix 100 ID/AST system (Becton Dickinson Co., Sparks, Md.) is an automated system for the identification and antimicrobial susceptibility testing of bacterial isolates. This system with its negative identification (NID) panel was evaluated for its accuracy in the identification of 507 isolates of the family Enterobacteriaceae, 57 other nonenteric gram-negative isolates that are commonly isolated in clinical microbiology laboratories, and 138 isolates of the family Vibrionaceae. All of the isolates had been characterized by using approximately 48 conventional tube biochemicals. Of the 507 isolates of the Enterobacteriaceae, 456 (89.9%) were correctly identified to the genus and species levels. The five isolates of Proteus penneri required an off-line indole test, as suggested by the system to differentiate them from Proteus vulgaris. The identifications of 20 (3.9%) isolates were correct to the genus level but incorrect at the species level. Two (0.4%) isolates were reported as "no identification." Misidentifications to the genus and species levels occurred for 29 (5.7%) isolates of the Enterobacteriaceae. These incorrect identifications were spread over 14 different genera. The most common error was the misidentification of Salmonella species. The shortest time for a correct identification was 2 h 8 min. The longest time was 12 h 27 min, for the identification of a Serratia marcescens isolate. Of the 57 isolates of nonenteric gram-negative bacilli (Acinetobacter, Aeromonas, Burkholderia, Plesiomonas, Pseudomonas, and Stenotrophomonas spp.), 48 (84.2%) were correctly identified to the genus and species levels and 7 (12.3%) were correctly identified to the genus level but not to the species level. The average time for a correct identification was 5 h 11 min. Of the Vibrionaceae spp., 123 (89.1%) were correctly identified at the end of the initial incubation period, which averaged 4 h. Based on the findings of this study, the Phoenix 100 ID/AST system NID panel falls short of being an acceptable new method for the identification of the Enterobacteriaceae, Vibrionaceae, and gram-negative nonenteric isolates that are commonly encountered in many hospital microbiology laboratories.     

Description and evaluation of the semiautomated 4-hour ATB 32E method for identification of members of the family Enterobacteriaceae

A study was performed to compare the rapid identification system ATB 32E (API-bioMérieux SA, La Balme-les-Grottes, France) with conventional biochemical methods for identifying 414 isolates of the family Enterobacteriaceae and the genus Aeromonas, mainly of clinical origin. Overall, 395 strains (95.4%) were correctly identified, with 48 (11.6%) requiring extra tests for complete identification. Ten strains (2.4%) were not identified, and nine (2.9%) were misidentified. The ATB 32E is a suitable alternative for rapid identification of members of the family Enterobacteriaceae.     

Accuracy of six commercially available systems for identification of members of the family vibrionaceae

Six commercially available bacterial identification products were tested with Vibrio alginolyticus (12 strains), V. cholerae (30 strains), Photobacterium (Vibrio) damselae (10 strains), V. fluvialis (10 strains), V. furnissii (4 strains), V. hollisae (10 strains), V. metschnikovii (9 strains), V. mimicus (10 strains), V. parahaemolyticus (30 strains), and V. vulnificus (10 strains) to determine the accuracy of each system for identification. The products included API 20E, Crystal E/NF, MicroScan Neg ID2 and Rapid Neg ID3, and Vitek GNI+ and ID-GNB. Each product was tested only with those species that were listed in its database. Overall, the systems correctly identified 63.9, 80.9, 63.1, 73.6, 73.5, and 77.7% of the isolates to species level, respectively. Error rates ranged from 0.8% for the API 20E to 10.4% for the Rapid Neg ID3. The API 20E gave "no identification" for 13.1% of the isolates, while the Neg ID2, GNI+, ID-GNB, and Crystal were unable to identify 1.8, 2.9, 5.0, and 6.9%, respectively. For V. cholerae, specifically, accuracy ranged from 50.0 to 96.7%, with the API 20E having the worst performance and Crystal having the best. V. fluvialis presented the biggest challenge for the API 20E and the GNI+, with probabilities averaging 10%, while V. mimicus was a major problem with the Crystal E/NF, which identified none of the strains correctly. With the Neg ID2, correct answers were often obtained only after a modified inoculation of the panel with a bacterial suspension prepared with 0.85% NaCl. Additional tests required for identification often included growth in the absence of NaCl, which is not readily available in most clinical laboratories. The only product to correctly identify at least 90% of V. cholerae strains was the Crystal E/NF, and only three of the six products, the API 20E and both of the Vitek cards, correctly identified more than 90% of the V. parahaemolyticus strains. Thus, extreme care must be taken in the interpretation of answers from these six commercially available systems for the identification of Vibrio species.     

Comparison of updated Vitek Yeast Biochemical Card and API 20C yeast identification systems.

The updated Vitek Yeast Biochemical Card (YBC) was compared with the API 20C by using 409 germ tube-negative yeasts and Geotrichum spp. that were either clinical or proficiency sample isolates. The API 20C was the reference standard. The 409 isolates represented nine genera and 21 species. Morphology agars were inoculated and interpreted for each isolate. The API 20C identified 406 isolates (99.3%), while the Vitek YBC identified 367 (89.7%). Both systems identified the majority of yeasts after 24 h of incubation--73.4% were identified by the API 20C and 77.4% were identified by the Vitek YBC. The Vitek 24-h reading had some incorrect identifications. These included 14 isolates of Candida tropicalis that were identified as Candida parapsilosis (91 to 97% reliability) and 3 isolates of Candida krusei that were called Blastoschizomyces capitatus (Geotrichum capitatum), Candida rugosa, and Candida zeylanoides. In total, the Vitek YBC misidentified 30 isolates, while the API 20C misidentified 3 isolates. In addition, results for 14 isolates with the Vitek YBC were listed under the category "no identification." Morphology agars were required for identification with 89 isolates (21.9%) when the API 20C was used and with 50 isolates (12.6%) when the Vitek YBC was used. Apart from the price of the Vitek instrument, the API 20C costs $1.28 more per test than the Vitek YBC. Overall, the updated Vitek YBC compares favorably with the API 20C in the identification of common yeasts such as Torulopsis glabrata, C. parapsilosis, and Cryptococcus neoformans. However, problems were encountered with the Vitek system in the identification of C. tropicalis, C. krusei, Trichosporon spp., and some Cryptococcus spp. The routine use of morphology agars with either method is recommended.     

Comparative evaluation of RapID ANA and API 20A for identification of anaerobic bacteria

This study evaluated RapID ANA and API 20 A systems for identification of anaerobic gram-positive and gram-negative bacteria isolated from oral and non-oral infections using standard reference methods. A total of 480 isolates were tested in both systems. The RapID ANA system correctly identified 74 % of the strains to species level and 17.5% to genus level; 5 % were misidentified. The API 20 A system correctly identified 50 % of the strains to species level and 24.5 % to genus level; 8 % were misidentified and 17.5 % could not be identified by the API 20 A system.     

Use of the API 20E system to identify veterinary Enterobacteriaceae.

A total of 503 veterinary enteric bacterial pathogens obtained from state veterinary diagnostic laboratories were tested on API 20E strips to determine whether this rapid microidentification system could be utilized for veterinary clinical microbiology. The API 20E strip accurately identified 96% of the veterinary isolates and misidentified 3%. Identifications by the API system and the diagnostic laboratories were in agreement in 85% of the isolates, disagreement on 16% of the isolates, and 1% were not identified by the API strip. Differences in identification occurred primarily in distinguishing between Klebsiella and Enterobacter and between Enterobacter and Escherichia coli. These disagreements were most often due to incorrect identifications by the diagnostic laboratory rather than by the API system. Biotype differences between human and veterinary isolates were compared. Significant differences were noted in several biochemical reactions. The main differences observed for E. coli isolates were in ornithine decarboxylase production and melibiose fermentation. The largest differences for Salmonella occurred in arginine dihydrolase production, citrate utilization, and inositol fermentation, whereas for Klebsiella pneumoniae the main differences were noted in urease production and nitrate reduction. These biotype differences, however, did not affect the accurate identification of organisms on the API strip.     

Comparison of the API Candida System with the AUXACOLOR System for Identification of Common Yeast Pathogens

Two commercial systems for the identification of yeasts were evaluated by using 159 clinical isolates that had also been identified by conventional biochemical and morphological methods. The API Candida system correctly identified 146 isolates (91.8%), and the AUXACOLOR system correctly identified 145 isolates (91.2%). However, of the 146 isolates identified by the API Candida system, 23 required supplemental biochemical tests or morphological assessment to obtain the correct identification. The AUXACOLOR system gave no identification in 13 cases (8.2%), while the API Candida system gave an unreadable profile in only one case. Incorrect identifications were more common with the API Candida system (12 isolates; 7.5%) than with the AUXACOLOR system (1 isolate; 0.6%).     

Comparison of Crystal Enteric/Nonfermenter system, API 20E system, and Vitek AutoMicrobic system for identification of gram-negative bacilli.

A comparative evaluation of the Crystal Enteric/Nonfermenter system (Crystal; Becton Dickinson, Cockeysville, Md.), API 20E (API; bioMérieux Vitek, Inc., Hazelwood, Mo.), and the Vitek GNI card (Vitek; bioMérieux Vitek) was performed with 512 clinical isolates of gram-negative bacilli, including 381 members of the family Enterobacteriaceae and 131 nonenteric bacilli. With supplemental testing, API, Crystal, and Vitek correctly identified to the genus and species level 505 (98.6%), 489 (95.5%), and 494 (96.5%) of the 512 isolates, respectively. Supplemental testing, as specified by the manufacturer, was required to identify 119 (23.2%), 18 (3.5%), and 5 (1.0%) of the isolates with the three systems, respectively. Of the 381 isolates from the family Enterobacteriaceae, API and Crystal correctly identified 90.3 and 91.6% by 18 to 24 h without supplemental testing, respectively, and Vitek identified 92.4 and 96.1% following 10 and 18 h of incubation, respectively. Of the 131 nonenteric organisms, API and Crystal correctly identified 28.2 and 93.9% by 18 to 24 h without supplemental testing, respectively, and Vitek identified 84.0% by 10 h and 93.9% by 18 h. Errors in identification with each system were infrequent and appeared to be randomly distributed among the genera evaluated. The three systems were comparable in accuracy when either a weighted clinical laboratory profile of organisms or a group of selected isolates in a stress test sample was evaluated (P > 0.05). There were no significant differences between the three systems in their ability to identify either the isolates in the weighted group or those in the stress test (P > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparative evaluation of the Eiken and API 20E systems and conventional methods for identification of members of the family Enterobacteriaceae

To evaluate the accuracy and utility of the Eiken Systek No. 1 (Eiken system; Eiken Chemical Co., Ltd., Tokyo, Japan), we conducted a clinical comparison, with 345 Enterobacteriaceae isolates, of the Eiken System with API 20E (Analytab Products, Inc., Plainview, N.Y.) and conventional methods. The Eiken system is a 21-biochemical-test battery tray stored at 25 degrees C and inoculated in one step. It is similar to the API 20E except that the Eiken system contains malonate, adonitol, and maltose; lacks gelatin, sucrose, melibiose, amygdalin, and arabinose; and uses reagent strips instead of liquid reagents. The API 20E and Eiken systems correctly identified 339 (97.7%) and 276 (79.5%), respectively, and misidentified 3 (0.9%) and 13 (3.7%), respectively, of the isolates. There were no identification codes for 5 (1.4%) organisms with the API 20E and 58 (16.7%) organisms with the Eiken system; of these latter unidentified organisms, 42 were identified as Proteus spp., Morganella sp., and Providencia rettgeri by conventional methods. There was no significant difference between the two rapid systems in total time required for inoculation and reading. Modifications for interpretation of decarboxylase and oxidase tests were needed for the Eiken system, and manipulation of reagent strips required considerable dexterity. However, the Eiken system was easier to inoculate than the API 20E, and, with minor increases in the data base to include more of the Proteus and Morganella spp. and P. rettgeri, the system should be reliable for identification of members of the family Enterobacteriaceae.     

Comparison of Minitek Anaerobe II, API An-Ident, and RapID ANA systems for identification of Clostridium difficile

Three commercial anaerobic systems, Minitek (BBL Microbiology Systems, Cockeysville, MD), API An-Ident (Analytab Products, Plainview, NY), and RapID ANA (Innovative Diagnostic Systems, Decatur, GA) were evaluated for ability to identify 45 Clostridium difficile isolates accurately. Minitek correctly identified 66% of C. difficile isolates to species, 27% were incompletely identified, and 7% were misidentified. Most of the discrepancies with Minitek were due to false negative biochemical results. API An-Ident correctly identified 9% C. difficile isolates to species, 89% were incompletely identified, and 2% were misidentified. Most of the API An-Ident discrepancies were due to the data base, which distinguished poorly between C. difficile, Clostridium hastiforme, and Clostridium sporogenes. RapID ANA correctly identified 100% of C. difficile isolates.     

Reproducibility of the analytab (API 20E) system.

The reproducibility of the Analytab (API 20E) system for identification of Enterobacteriaceae was evaluated with 110 clinical isolates. Each isolate was identified by two technologists at different times. Genus-species identification was 97.3% reproducible; however, only 55.5% of the strains gave identical reactions in all 20 of the API 20E biochemical tests on repeat testing. Of those strains which varied, 56% possessed only one variable biochemical test. The reproducibility for each biochemical test was calculated and ranged from 89 to 100%. A subset of 20 of the most variable strains was tested further under conditions of varying incubation time (15 and 22 h) and inoculum concentration (10(7), 10(5), and 10(3) colony-forming units per ml), and by having four technologists interpret the test results. The reproducibility for each biochemical test for these 20 variable strains ranged from 86 to 99%. Less variation in interpretation by technologists was seen at an incubation time of 22 h and an inoculum concentration of 10(7) colony-forming units per ml. Consideration of the reproducibility for each biochemical test can aid in determining the probability that two isolates suspected of being the same strain, but with API profiles which differ by one or more biochemical test results, are in fact the same strain. Variables such as inoculum size, incubation time, technologist interpretation, and strip variability affect the API test results and should be standardized to minimize their effects.