Evaluation of the Vitek 2 ID-GNB assay for identification of members of the family Enterobacteriaceae and other nonenteric gram-negative bacilli and comparison with the Vitek GNI+ card

We evaluated the Vitek 2 ID-GNB identification card (bioMérieux, Inc., Durham, N.C.) for its ability to identify members of the family Enterobacteriaceae and other gram-negative bacilli that are isolated in clinical microbiology laboratories. Using 482 enteric stock cultures and 103 strains of oxidase-positive, gram-negative glucose-fermenting and nonfermenting bacilli that were maintained at -70 degrees C and passaged three times before use, we inoculated cards according to the manufacturer's directions and processed them in a Vitek 2 instrument using version VT2-R02.03 software. All panel identifications were compared to reference identifications previously confirmed by conventional tube biochemical assays. At the end of the initial 3-h incubation period, the Vitek 2 instrument demonstrated an accuracy of 93.0% for the identification of enteric strains; 414 (85.9%) were correctly identified at probability levels ranging from excellent to good, and an additional 34 (7.1%) strains were correctly identified but at a low level of discrimination. Nineteen (3.9%) strains were unidentified, and 15 (3.1%) were misidentified. The 19 unidentified strains were scattered among 10 genera. Three of the 15 misidentified strains were lactose-positive Salmonella spp. and were identified as Escherichia coli; another was a lactose-positive, malonate-negative Salmonella enterica subsp. arizonae strain that was identified as E. coli. Of the 103 glucose-fermenting and nonfermenting nonenteric strains, 88 (85.4%) were correctly identified at probability levels ranging from excellent to good, and 10 (9.7%) were correctly identified, but at a low level of discrimination, for a total of 95.1% accuracy with this group. Two strains were unidentified and three were misidentified. The errors occurred for strains in three different genera. With the increased hands-off approach of the Vitek 2 instrument and accuracies of 93% for the identification of enteric organisms and 95.1% for the identification of nonenteric organisms with the ID-GNB card, use of this product presents an acceptable method for the identification of most gram-negative organisms commonly isolated in the clinical laboratory. A comparison of these results to those obtained by testing 454 of the same strains with the Vitek GNI+ card revealed no significant difference in the abilities of the two cards to identify these organisms accurately.     

Clinical evaluation of the RapID-ANA II panel for identification of anaerobic bacteria.

The accuracy of the RapID-ANA II system (Innovative Diagnostic Systems, Inc., Atlanta, Ga.) was evaluated by comparing the results obtained with that system with results obtained by the methods described by the Virginia Polytechnic Institute and State University. Three hundred anaerobic bacteria were tested, including 259 clinical isolates and 41 stock strains of anaerobic microorganisms representing 16 genera and 48 species. When identifications to the genus level only were included, 96% of the anaerobic gram-negative bacilli, 94% of the Clostridium species, 83% of the anaerobic, nonsporeforming, gram-positive bacilli, and 97% of the anaerobic cocci were correctly identified. When correct identifications to the genus and species levels were compared, 86% of 152 anaerobic gram-negative bacilli, 76% of 34 Clostridium species, 81% of 41 anaerobic, nonsporeforming, gram-positive bacilli, and 97% of 73 anaerobic cocci were correctly identified. Eight isolates (3%) produced inadequate identification in which the correct identification was listed with one or two other possible choices and extra tests were required for separation. A total of 9 isolates (3%) were misidentified by the RapID-ANA II panel. Overall, the system was able to correctly identify 94% of all the isolates to the genus level and 87% of the isolates to the species level in 4 h by using aerobic incubation.     

Evaluation of autoSCAN-W/A automated microbiology system for the identification of non-glucose-fermenting gram-negative bacilli.

We evaluated the ability of the autoSCAN-W/A (MicroScan Division, Baxter Healthcare Corporation, West Sacramento, Calif.), in conjunction with the dried colorimetric Neg ID type 2 panel (DCP) and new rapid fluorometric Neg ID panel (RFP), to identify non-glucose-fermenting gram-negative bacilli by challenging the system with 310 previously identified reference strains. Of these 310 isolates, 286 organisms were in the DCP data base and 269 were in the RFP data base. Use of the DCP panels resulted in 118 (41.3%) correct and 64 (22.4%) incorrect first choice identifications at greater than or equal to 85% probability, 61 (21.3%) low-probability identifications, and 43 (15.0%) reports of unidentified organisms. The RFP system reported 135 (50.1%) correct and 25 (9.3%) incorrect identifications at greater than or equal to 85% probability and 109 (40.5%) low-probability identifications. Unidentified isolates (DCP system only) and isolates producing low-probability first choice identifications (both systems) required supplementary biochemical testing. Over half (37 of 64 [57.8%]) of the DCP misidentifications were due to four commonly isolated, saccharolytic organisms (Alcaligenes xylosoxidans subsp. xylosoxidans, Pseudomonas putida, Pseudomonas fluorescens, and Xanthomonas maltophilia), while 7 of 25 (28%) of misidentifications in the RFP system were due to P. fluorescens. Of note, the RFP system identified non-glucose-fermenting gram-negative bacilli within 2 h of panel inoculation, allowing additional conventional biochemical tests to be set up the same day on low-probability isolates, whereas only 13.5% of the DCPs could be read at 18 h, with the remainder requiring 42 h of incubation before reading. When organism identifications were recalculated with the updated RFP data base and revised software, only 8.1% of all 310 isolates were misidentified at greater than or equal to 85% probability while 77.1% of the isolates were now correctly reported at this same high probability.     

Evaluation of the MicroScan rapid neg ID3 panel for identification of Enterobacteriaceae and some common gram-negative nonfermenters

The MicroScan Rapid Neg ID3 panel (Dade Behring, Inc., West Sacramento, Calif.) is designed for the identification of gram-negative bacilli. We evaluated its ability to accurately identify Enterobacteriaceae that are routinely encountered in a clinical laboratory and glucose nonfermenting gram-negative bacilli. Using 511 stock cultures that were maintained at -70 degrees C and passaged three times before use, we inoculated panels according to the manufacturer's instructions and processed them in a Walk/Away instrument using version 22.01 software. The time to identification was 2 h and 30 min. All panel identifications were compared to reference identifications previously determined by conventional tube biochemicals. At the end of the initial 2.5-h incubation period, 405 (79.3%) identifications were correct. An additional 49 (9.6%) isolates were correctly identified after required additional off-line biochemical tests were performed. Thus, at 24 h, 88.8% of the 511 strains tested were correctly identified. Twenty-two (4.3%) were identified to the genus level only. Twenty-six (5.1%) strains were misidentified. Because the system is based on fluorogenics, there are no conventional tests readily available with which to compare possibly incorrect reactions. Of the 28 Salmonella strains that were tested, 5 were incorrectly reported. The 21 remaining errors were scattered among the genera tested. Testing on nine strains gave a result of "no identification" (very rare biotype). The Rapid Neg ID3 panel in this study approached 89% accuracy for the identification of gram-negative organisms encountered in the hospital laboratory.     

Antibacterial activity of norfloxacin against bacterial isolates from the urinary tract

Two hundred fourteen isolates from clinical specimens were tested in vitro to determine their susceptibility pattern against norfloxacin. Of the 151 strains of gram-negative bacteria tested, 149 (98.7%) were susceptible. Sixty-three (100%) of the gram-positive bacteria tested were also susceptible to norfloxacin. Norfloxacin showed excellent activity against all bacteria isolated from urine.     

Evaluation of the Sceptor system for identification of bacteria of veterinary origin.

The Sceptor system (Becton Dickinson Diagnostic Instrument Systems, Towson Md.) was assessed for its ability to identify veterinary clinical isolates. A total of 605 bacteria, including 315 isolates of the family Enterobacteriaceae, 191 gram-negative nonenteric bacteria, and 99 gram-positive bacteria, were tested. Overall, 534 (88.3%) were correctly identified, 28 (4.6%) were not identified, 12 (2.0%) were incorrectly identified at the genus levels, and 32 (5.3%) were incorrectly identified at the species level. The Sceptor system correctly identified 292 (92.7%) isolates of Enterobacteriaceae, 165 (86.4%) gram-negative nonenteric bacteria, and 77 (77.8%) gram-positive bacteria. One hundred thirty organisms not contained in the data base were tested with the Sceptor system to assess the possibility of expanding the data base. The Sceptor system was an acceptable method for the identification of isolates of Enterobacteriaceae but not gram-negative nonenteric and gram-positive bacteria of animal origin. Development of a veterinary isolate-specific data base would improve the utility of the Sceptor system in veterinary diagnostic bacteriology.     

Premarket evaluation of IDS RapID SS/u system for identification of urine isolates.

A total of 170 fresh clinical urine isolates were tested with a premarket configuration of the RapID SS/u system (Innovative Diagnostic Systems, Inc., Atlanta, Ga.), a qualitative micromethod for the identification of selected organisms commonly isolated from urine specimens. Results were compared with those obtained with conventional methods of identifying gram-positive isolates and with the AutoMicrobic system (Vitek Systems, Inc., Hazelwood, Mo.), utilizing Gram-Negative Identification cards for the identification of gram-negative rods. Organisms representing 12 taxa were included in the study. Of the 170 isolates, 163 (95.9%) were correctly identified. A total of 144 strains (84.7%) were correctly identified without additional testing, whereas 19 isolates (11.2%) required further testing. Seven isolates (4.1%) were incorrectly identified. The SS/u system required minimal hands-on time inoculate and interpret reactions. Discrepancies most often occurred with regard to misinterpretation of Escherichia coli and Enterobacter sp. as Citrobacter sp. The IDS RapID SS/u system may indeed prove valuable for the rapid manual identification of urine isolates.     

Evaluation of an automated system for identification of anaerobic bacteria

A fully automated computer-assisted system (ATB system, bioMérieux, France) which uses disposable microenzymatic panels was evaluated for its ability to identify 215 strains of anaerobic bacteria (clinical isolates and reference strains). All strains were examined using conventional identification protocols and by gas chromatographic analysis of short-chain fatty acids. Automated reading of Rapid ID32A test kits (bio-Mérieux, France) by the ATB system gave correct identification for 195 strains (90.7 %): 92.25 % of gram-negative anaerobes (116 strains) and 89 % of gram-positive anaerobes (99 strains) were correctly identified. Twelve strains (5.6 %) were incorrectly identified and 8 strains (3.7 %) were not identified by the system. For some strains in theBacteroides fragilis group, forClostridium difficile and for theFusobacterium genus, additional tests suggested by the ATB software were necessary to reach a final identification at the species or genus level. On the basis of the high incidence of correct identifications and the comparison of these results with those obtained previously using other commercially available kits, the ATB system was found to be a reliable method for identification of anaerobic bacteria in clinical laboratories.     

Evaluation of the IDS RapID SS/u system for rapid identification of urinary microorganisms

The accuracy of a new rapid identification system for common urinary pathogens was compared with that of conventional methods and of miniaturized 18-24-hour identification panels. The rapid system, RapID SS/u (Innovative Diagnostic System Inc., Atlanta, GA) is a non-growth-dependent micro-method that identifies selected gram-negative bacilli, gram-positive cocci, and yeasts in two hours by detection of constitutive enzymes acting on chromogenic substrates. A total of 185 representative clinical urinary isolates were tested, including 24 gram-positive cocci, 140 gram-negative bacilli, and 21 yeasts. Identifications by the rapid system were compared with the ones obtained by reference conventional methods for gram-positive cocci and yeasts. For gram-negative bacilli, identifications were compared with the ones obtained by MicroScan Combo Panel (American MicroScan, Mahwah, NJ), and all discrepancies were resolved by testing with API 20E (Analytab Products, Plainview, NY). Overall, the RapID SS/u system correctly identified to genus 160 of 185 isolates (86.5%). For 14 additional isolates (7.6%) the system provided probability overlap identifications that required further testing. Two (1%) isolates failed to be identified, and nine isolates (4.9%) were misidentified by the system. Discrepancies involved five strains of Citrobacter, one Enterobacter, one Morganella, and one Providencia species. The authors conclude that the RapID SS/u system provided rapid and accurate genus identification of most microorganisms commonly isolated from urine.     

Use of the MicroSeq 500 16S rRNA gene-based sequencing for identification of bacterial isolates that commercial automated systems failed to identify correctly

Reliable automated identification and susceptibility testing of clinically relevant bacteria is an essential routine for microbiology laboratories, thus improving patient care. Examples of automated identification systems include the Phoenix (Becton Dickinson) and the VITEK 2 (bioMerieux). However, more and more frequently, microbiologists must isolate "difficult" strains that automated systems often fail to identify. An alternative approach could be the genetic identification of isolates; this is based on 16S rRNA gene sequencing and analysis. The aim of the present study was to evaluate the possible use of MicroSeq 500 (Applera) for sequencing the 16S rRNA gene to identify isolates whose identification is unobtainable by conventional systems. We analyzed 83 "difficult" clinical isolates: 25 gram-positive and 58 gram-negative strains that were contemporaneously identified by both systems--VITEK 2 and Phoenix--while genetic identification was performed by using the MicroSeq 500 system. The results showed that phenotypic identifications by VITEK 2 and Phoenix were remarkably similar: 74% for gram-negative strains (43 of 58) and 80% for gram-positive strains were concordant by both systems and also concordant with genetic characterization. The exceptions were the 15 gram-negative and 9 gram-positive isolates whose phenotypic identifications were contrasting or inconclusive. For these, the use of MicroSeq 500 was fundamental to achieving species identification. In clinical microbiology the use of MicroSeq 500, particularly for strains with ambiguous biochemical profiles (including slow-growing strains), identifies strains more easily than do conventional systems. Moreover, MicroSeq 500 is easy to use and cost-effective, making it applicable also in the clinical laboratory.     

Evaluation of the Phadebact coagglutination test for the rapid serotyping ofHaemophilus influenza

Conventional tests for the indentification ofHaemophilus species require 24–48 h for completion. In this study, we evaluated the Phadebact coagglutination method for the serotyping ofHaemophilus that yields results within 2 min. Of the 150 strains tested, 148 wereH. influenzae and 2 wereH. parainfluenzae. Of the 83H. influenzae isolates from cerebrospinal fluid and blood 80 were correctly typed as b by the Phadebact test. Of the 51 sputum isolates, 48 (94%) were nontypable. Eleven (69%) of the remaining sixteen isolates from secondary and unknown sources were type b, four (25%) were nontypable, and one (6%) was in the acdef group. Thirty gram-positive and gram-negative bacteria other thanHaemophilus were also tested with no false-positive reactions. The Phadebact test is rapid and easy to perform and interpret.     

Evaluation of an Automated System for Identification of Enterobacteriaceae and Nonfermenting Bacilli

 The performance of the Vitek 2 (bioMérieux, France), a new fully automated system allowing rapid identification of microorganisms and susceptibility testing, and the Vitek 2 ID-GNB card (bioMérieux) was evaluated using 502 clinical isolates and stock collection strains of gram-negative rods belonging to 70 taxa. The number of isolates correctly identified to species and genus levels was 430 (85.7%) and 485 (96.6%), respectively. Clinical isolates of both Enterobacteriaceae and non-Enterobacteriaceae were better identified at the species level (95.3% and 74%, respectively) than stock collection strains (86.4% and 52.2%, respectively). The Vitek 2 ID-GNB card provides after 3 h a highly acceptable level of accuracy for identification of Enterobacteriaceae and non-Enterobacteriaceae, including most atypical strains encountered in clinical situations.     

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.     

Clinical evaluation of the Vitek ANI card for identification of anaerobic bacteria.

An evaluation of the Vitek Anaerobe Identification (ANI) card was performed with 341 bacterial isolates, including 313 clinical isolates and 28 stock strains of anaerobic microorganisms. Identifications obtained with the ANI card were compared with those determined by conventional methods. The card identified 73.2% of 149 anaerobic gram-negative bacilli, 63.6% of 44 Clostridium spp., 65.8% of 38 anaerobic nonsporeforming gram-positive bacilli, and 69.1% of 110 anaerobic cocci, with no further testing required. When genus-level identifications were included, 83.9% of the anaerobic gram-negative bacilli, 70.5% of Clostridium spp., 73.7% of the anaerobic nonsporeforming gram-positive bacilli, and 73.6% of the anaerobic cocci were identified. Nineteen isolates (5.6%) produced identifications of good confidence but marginal separation or questionable biotype, in which the correct identification was listed with one or two other possible choices and extra tests were required and suggested. A total of 28 (8.2%) were not identified and 29 isolates (8.5%) were misidentified by the ANI card. Among the commonly isolated clinically significant anaerobes, the ANI card identified 100% of 55 Bacteroides fragilis and 100% of 8 Clostridium perfringens. Use of supplemental tests and expansion of the data base to include additional strains of organisms that are difficult to separate even with conventional methods may improve the accuracy of the ANI card as a method for identification of anaerobic bacteria in the clinical laboratory.     

Rapid automated identification of gram-negative bacilli from blood cultures with the AutoMicrobic system.

Automated identification of gram-negative bacilli directly from blood culture bottles by using the AutoMicrobic System (AMS) was evaluated with a modified procedure for the AMS Enterobacteriaceae-plus nonfermenter identification card. A total of 150 strains were tested (44 clinical and 106 seeded) and compared with a conventional identification procedure. These strains included 107 Enterobacteriaceae and 43 oxidase-positive or glucose-nonfermenting, or both, organisms. AMS identifications on one of these strains were not interpretable owing to equal probability AMS identification values. Of the remaining 149 strains, 138 (92.6%) were correctly identified within 8 to 13 h of the first reading. Of 69 identifications analyzed after 6 h of incubation, 91% were correct. This procedure was found to be rapid, convenient, and nonlabor intensive and is recommended for presumptive identification of gram-negative bacilli in blood cultures.     

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.     

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.     

Validation of the automated reading and incubation system with Sensititre plates for antimicrobial susceptibility testing

The present study compared the antimicrobial susceptibility testing (AST) results generated by the Automated Incubation and Reading System (ARIS) with custom Sensititre plates (TREK Diagnostic Systems, Cleveland, Ohio) and MicroScan PC10 GP and NUMIC10 GN plates interpreted with the WalkAway-96 system (Dade Behring, West Sacramento, Calif.) for gram-positive (GP) and gram-negative (GN) organisms as part of an in-house validation. A total of 326 isolates (3,689 antimicrobial agent-organism combinations) were evaluated. Sensititre plates were inoculated according to the instructions of the manufacturer with a suspension adjusted to a 0.5 McFarland standard, while the Prompt Inoculation System was used for the MicroScan plates. ARIS and the WalkAway system were used for automated reading of the Sensititre and MicroScan plates, respectively, at 18 to 24 h. The results were analyzed for essential (+/-1 twofold dilution) and categorical (sensitive, intermediate, or resistant) agreements. Plates that resulted in ARIS interpretations with major (falsely resistant) or very major (falsely susceptible) errors compared to the results obtained with the WalkAway system were read manually to corroborate instrument readings. Isolates for which very major or major errors were obtained and for which the results were not resolved by manual reading were retested in parallel. Isolates for which very major or major errors were obtained and for which the results were not resolved upon repeat testing were tested by the National Committee for Clinical Laboratory Standards M7-A5 frozen reference microdilution method. Essential agreement was 95.8% for 246 GN isolates. The following categorical error rates were obtained for the GN isolates: 1.3% minor errors, 0% major errors, and 0.4% very major errors. For 95 GP isolates, there was 93.5% essential agreement. Categorical error rates for GP isolates were 0.9% minor errors, 0.6% major errors, and 0.4% very major errors. ARIS-Sensititre is a diagnostic system feasible for use for automated AST in a clinical laboratory.     

Evaluation of the KOH test and the antibiotic disk test in routine clinical anaerobic bacteriology.

We have evaluated the KOH test, the antibiotic disk identification test, and the Gram stain reaction for the preliminary grouping of gram-positive and gram-negative anaerobes and have assessed the value of erythromycin 60-micrograms-disk resistance as a predictive index of clindamycin resistance among anaerobes. By testing 931 clinical isolates, 281 gram positive and 650 gram negative, with the KOH test and vancomycin 5-micrograms-disk test, we obtained the following parameters: sensitivity, 89.7 and 97.1%; specificity, 97.5 and 98.3%; positive predictive value, 80.4 and 98.7%; and efficiency, 92.1 and 98% for the KOH test and the vancomycin test, respectively. The KOH reaction incorrectly grouped 42 of 97 Bacteroides bivius and 12 of 50 pigmented Bacteroides strains. The vancomycin test correctly identified 63 of 67 gram-negative strains that had given a negative KOH reaction. The erythromycin disk result correctly predicted clindamycin resistance in gram-negative isolates but had a sensitivity of 85.7%, a specificity of 92.4%, and a positive predictive value of 42.8% for gram-positive isolates. Therefore, the use of these preliminary identification tests can assist in the correct grouping of anaerobes and accurately predict significant clindamycin resistance in gram-negative anaerobic bacteria.     

Evaluation of the VITEK 2 System for Rapid Identification of Medically Relevant Gram-Negative Rods

The new VITEK 2 system (bioMérieux) was evaluated at two independent sites with the identification card for gram-negative bacilli (ID-GNB card). Of the 845 strains tested, which represented 70 different taxa belonging to either the family Enterobacteriaceae or the nonenteric bacilli, 716 (84.7%) were correctly identified at the species level. Thirty-two (3.8%) additional strains were identified to the species level after the performance of simple, rapid manual tests (oxidase, hemolysis, indole reaction, motility, and pigmentation). For 80 (9.5%) strains, these additional tests did not lead to an identification at the species level but the correct species identification was given among the organisms listed. Only 7 (0.8%) strains were misidentified, and 10 (1.2%) were not identified. Mistakes were randomly distributed over different taxa. Due to the new, more sensitive fluorescence-based technology of the VITEK 2 system, final results were available after 3 h. Since our evaluation was mainly a stress test, it is predicted that the VITEK 2 system in conjunction with the ID-GNB card would perform well under conditions of a routine clinical laboratory in identifying members of the family Enterobacteriaceae and selected species of nonenteric bacteria. This system is a promising, highly automated new tool for the rapid identification of gram-negative bacilli from human clinical specimens.