JOURNAL OF CLINICAL MICROBIOLOGY, Mar. 1982, p. 419-424 Vol. 15, No. 30095-1137/82/030419-06$02.00/0

Evaluation of the Enteric-Tek System for IdentifyingEnterobacteriaceae

A. 0. ESAIAS,* D. L. RHODEN, AND P. B. SMITHCenter for Infectious Diseases, Centers for Disease Control, Atlanta, Georgia 30333

Received 26 June 1981/Accepted 5 October 1981

The Enteric-Tek wheel (Flow Laboratories), consisting of 14 different biochem-ical parameters for rapidly identifying Enterobacteriaceae, was evaluated andcompared with the conventional method for completely identifying 301 entericcultures, representing 36 species. The Enteric-Tek system correctly identified 264(97.8%) of the 270 common or typical strains and 26 (83.9%) of the 31 unusual oratypical strains tested, demonstrating an overall identification accuracy rate of96.3%. There were 80 (26.6%) correctly identified strains requiring additionaltests. Of the 11 (3.6%) misidentifications, 5 (3 Klebsiella and 2 Salmonella strains)were correctly identified at the genus level. When 4,228 individual tests in theEnteric-Tek wheel were compared with the conventional tubed media, 96.4% ofthe tests agreed; urease, citrate, adonitol, and lactose agreed less than 97%. TheEnteric-Tek system was found to be reliable and accurate in producing identifica-tions at the genus and species level within 18 to 24 h.

Since a substantial proportion of the workloadgenerated in the clinical microbiology laboratoryinvolves isolating and identifying Enterobacteri-aceae, the development of rapid identificationsystems for enteric bacteria has increased, asevidenced by the numerous commercially avail-able kits (2, 14). Many of these systems havebeen studied and evaluated by various investiga-tors. A new commercial identification system,the Enteric-Tek wheel (Flow Laboratories, Ros-lyn, N.Y.), is designed to identify the Entero-bacteriaceae at the genus and species levelwithin 18 to 24 h of isolation on primary platingmedia. By the use of 14 different biochemicalparameters, the system generates a five-digitoctal profile number derived from the biochemi-cal reactions. In our study, interpretation of thereactions was made according to the manufac-turer's recommendations so an identificationcould be derived from the computer code book.The purpose of this evaluation was to deter-

mine the ability of the Enteric-Tek system toidentify both typical and atypical members ofEnterobacteriaceae. This study presents datawhich describe the performance and accuracy ofthe Enteric-Tek wheel as compared with a con-ventional identification system.

MATERIALS AND METHODSBacterial cultures tested. We tested 301 of our stock

cultures from the General Bacteriology Laboratory,Centers for Disease Control, culture collection. Thesecultures had been assigned code numbers by a thirdparty. The selected cultures, well distributed among 36species, included 270 common or typical strains and 31

unusual or atypical strains. All cultures were main-tained in sealed Trypticase (BBL Microbiology Sys-tems, Cockeysville, Md.) soy agar stabs and stored atrodm temperature in the dark. Each culture had previ-ously been identified by conventional procedures (5,8-11). The identity of each culture remained unknownuntil all results were compiled and the testing wascompleted.

Conventional method for identification. Each culturewas streaked onto a MacConkey agar plate and ablood agar plate. Cultures were then identified byconventional biochemical tests (5, 8-10). The conven-tional tests routinely performed included reactions ontriple sugar iron agar (H2S production); Christensenurea agar; indole; methyl red; Voges-Proskauer (VP)medium; citrate; lysine and omithine decarboxylase;arginine dihydrolase; motility; phenylalanine; malon-ate; o-nitrophenyl-o-D-galactopyranoside; and pro-duction of acid from glucose, lactose, sorbitol, dulci-tol, inositol, adonitol, mannitol, sucrose, salicin,arabinose, raffinose, and rhamnose. These media wereinoculated from culture suspensions in tryptone brothand were incubated at 35C. After 18 to 24 h ofincubation, reagents were added for indole, methylred, VP (acetoin), and phenylalanine tests. Testswhich were not positive within 18 to 24 h wereobserved for a maximum of 7 days. When required,additional tests were performed to complete the identi-fication, e.g., growth in KCN and serological confir-mation of Salmonella and Shigella. All cultures wereidentified by the nomenclature and taxonomy de-scribed by Edwards and Ewing (8, 9) and Brenner etal. (5). When necessary, the Enterobacteriology Sec-tion, CDC, was consulted as a reference laboratory.

Enteric-Tek system. The Enteric-Tek system is around, multicompartment wheel, consisting of a cen-tral well and 11 individual peripheral wells, all ofwhich contain solid media. The system provides for

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determining 14 different biochemical parameterswhich include: indole production; tryptophan deami-nase; H2S production; citrate; malonate; lysine andornithine decarboxylase; urease; and acid productionfrom glucose, lactose, rhamnose, adonitol, sorbitol,and arabinose. All organisms tested were inoculatedonto MacConkey agar and blood agar plates andincubated for 18 to 24 h at 35°C. A suspension fromseveral well-isolated colonies of each organism wasmade in 2 ml of sterile distilled water. Before inocula-tion, the wheels were allowed to warm to roomtemperature and were labeled appropriately. Inocula-tion was done as described in the detailed instructionsprovided by the manufacturer. Each wheel was placedin an upright position, incubated at 35°C for 18 to 24 h,then removed from the incubator, and observed forcolor changes in the solid media. The only manipula-tion required to observe a biochemical reaction in-volved rolling a cotton swab saturated with a specialindole reagent (Flow Laboratories) over growth in thecenter well. Any redness developing within 30 s indi-cated a positive indole reaction. The remainder of thewells were visually observed, and their color was read,as suggested by the manufacturer. All reactions wererecorded on a printed form and tabulated into a five-digit profile number for identifying organisms listed inthe manufacturer's code book. The data incorporatedinto the computer code book were generated from thepercentage charts of Edwards and Ewing (8) and fromin-house studies. Identification was based on the prob-ability that a set of biochemical reactions would occurwith more likelihood for one particular organism thanfor another and allowed for the possibility of atypicalreactions. The code book lists additional biochemicaltests required to complete an identification. The addi-tional tests include: arginine, cellobiose, DNase, escu-lin, gas from glucose, inositol, Jordan tartrate, potassi-um cyanide, maltose, mannitol, methyl red, motility,raffinose, VP, xylose, and serology for Salmonella andShigella.

RESULTSAgreement of tests. Biochemical reactions for

the various tests in the Enteric-Tek system werecompared with those obtained by the conven-tional method. Of the 14 common tests, 10showed more than 97% agreement with theirconventional counterparts, whereas urease, ci-trate, adonitol, and lactose agreed 83.4, 91.4,94.0, and 94.4%, respectively.These four tests comprised 75% of all of the

test discrepancies. Certain groups of organismswere responsible for lowering the agreement forsome of the tests. The 50 differences in theurease test, all false-positive in the Enteric-Teksystem except for 1, occurred with 6 Citrobacterfreundii, 10 Citrobacter diversus, 14 Citrobacteramalonaticus, 4 Klebsiella pneumoniae, 4 Kleb-siella oxytoca, 8 Enterobacter cloacae, 1 Hafniaalvei, 1 Morganella morganii, and 1 Yersiniaenterocolitica strain. One Proteus rettgeri straingave a false-negative reaction despite a 4+ reac-tion in the conventional Christensen urea agarslant. The 26 citrate test discrepancies included

22 false-negatives and 4 false-positives but werenot responsible for any misidentifications. Ofthe 18 differences in the adonitol test, all of the11 strains of Serratia marcescens, 1 Serratialiquefaciens, 1 K. pneumoniae, 1 Shigella flex-neri, 2 Yersinia pseudotuberculosis, and 1 Y.enterocolitica strain were false-positive, butonly 2 of the latter 3 cultures were misidentified.One false-negative adonitol reaction occurredwith a Providencia alcalifaciens strain. The 17discrepancies in lactose were divided almostequally between the false-negative (9) and false-positive (8) reactions. Differences in the lactoseresults did not change the identifications.

Identification. Overall, the Enteric-Tek sys-tem correctly identified, at the genus and specieslevel, 96.3% of the 301 strains tested. As shownin Table 1, the system correctly identified 264(97.8%) of the typical strains and 26 (83.9%) ofthe atypical strains. Of the 290 cultures correctlyidentified, 62 of 270 typical strains (23.0%) and18 of 31 atypical strains (58.1%) required addi-tional tests. The number of additional testsranged from one test for 7 strains, two tests for42 strains, and three tests for 30 strains, to fivetests for 1 atypical Escherichia coli strain. Weperformed the suggested additional tests whenan identification was given with less than 95%probability. Although correct identifications forone Arizona hinshawii, one S. flexneri, twoShigella boydii, and one Y. enterocolitica werelisted as first-choice identifications, serologicalconfirmation was required because the givenprobabilities were less than 95%. Twenty-onestrains required serological confirmation be-cause the assigned identifications were listed assecond, third, and fourth choices in the codebook.The identification accuracy of individual spe-

cies by the Enteric-Tek system is shown inTable 2. The system provided 252 (86.9%) of thecorrect identifications as the first choice. Therewere 38 identifications listed as second, third, orfourth choices (29 as second, 6 as third, and 3 asfourth). The Enteric-Tek system correctly iden-tified 100% of the strains for 29 of 36 species(80.6%) tested. The number of strains tested foreach species ranged from 2 to 14, except for 25E. coli strains, which included H2S-positive andatypical strains. Two atypical strains of both E.coli and C. freundii were misidentified, decreas-ing their identification rates from 100% to 92 and82%, respectively. Four strains each of Salmo-nella paratyphi A, Salmonella typhi, and Y.enterocolitica were tested; one strain of eachwas misidentified, resulting in a 75% identifica-tion rate for each species. The misidentifiedstrain of S. typhi was atypical. Both Salmonellastrains were identified as S. enteritidis, listed asthe second choice in the manufacturer's comput-

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EVALUATION OF THE ENTERIC-TEK SYSTEM 421

TABLE 1. Summary of identifications of unknown cultures with the Enteric-Tek system

Organism category No. tested No. correct No. correct requiringOrganismcategoryNo. tested ~~~~~~~~~~~~~~additionaltests'

Common or typical 270 264 (97.8)b 62 (23.0)cUnusual or atypical 31 26 (83.9) 18 (58.1)Total 301 290 (96.3) 80 (26.6)

a Including Salmonella and Shigella serology when required.b Number in parentheses gives the percentage for the category.c Number in parentheses indicates the percentage of the number correct in the category.

er code book. Klebsiella ozaenae, with ninestrains tested, showed the lowest identificationrate (66.6%), because three strains did not meetthe expected species level of identification, asclaimed by the manufacturer.

DISCUSSIONIn comparison with the conventional meth-

ods, the Enteric-Tek system demonstrated ahighly acceptable level of identification accura-cy for the 301 stock cultures tested. The overallidentification rate of the Enteric-Tek system(96.3%) compares favorably with the Micro-media' System (97%) and Entero-Set 20 (96%)and is better than the Micro-ID (94%), API 20E(92%), and Enterotube (84%) systems wheneach system is compared with conventionalmethods (2, 14). Another study reported a higheridentification rate (97%) for both the API 20Eand Micro-ID systems (3). Thirty-six entericspecies were tested with the Enteric-Tek wheel,as compared with 21 to 28 enteric species testedwith the other rapid identification kits. For iden-tifying a large variety of enteric bacterial strainsto the species level, the Enteric-Tek systemshows potential advantages over some of therapid systems previously evaluated (2-4, 6, 14).The Enteric-Tek system can correctly identifySerratia strains as to species, whereas the API20E system has frequently been reported toidentify them at the genus level only (4, 14).Additionally, a test for adonitol fermentation isincluded in this system, as in the Micro-ID andEntero-Set 20 but not in API 20E, allowing forthe differentiation of H2S-negative C. freundiifrom C. diversus without the need for additionaltests (4). Unlike the Micro-ID data base, theEnteric-Tek system includes identification forEnterobacter gergoviae and C. amalonaticusstrains (6).

Additional species of varied levels of difficultywere used in this study, and the Enteric-Teksystem correctly identified all strains for 29 of 36species (81%) tested. By comparison, 20 entericspecies were tested against the following rapidsystems, with the indicated number of specieshaving all of their strains correctly identified: theMicro-Media system with 17 (85%), Micro-ID

with 13 (65%), Enterotube with 12 (60%), andAPI 20E with 11 (55%) (14). The scope of theEnteric-Tek system data base was demonstratedby the 185 different profile numbers generated inderiving the identifications, with a range of 1 to 9different profile codes for each species tested.The Enteric-Tek system showed the ability toidentify two new Serratia species, S. fonticolaand S. odorifera. This ability was clearly shownwhen the one S. odorifera strain tested wascorrectly identified as a first-choice identifica-tion, having a 87.71% probability. Also, with 8of 10 correctly identified Enterobacter aero-genes strains, the Enteric-Tek system listed S.fonticola, E. aerogenes, and S. odorifera, in thatorder, as first-, second-, and third-choice identi-fications. E. aerogenes was given as a second-choice identification, showing a 47.07% proba-bility, as compared with S. fonticola (52.91%)and S. odorifera (0.02%). In both of these situa-tions, two additional tests, VP and DNase, weresuggested by the manufacturer to easily differen-tiate these species. All S. fonticola strains arelisted as VP negative, whereas all E. aerogenesstrains are VP positive. All strains for both S.fonticola and E. aerogenes have been shown tobe DNase negative, whereas all S. odoriferastrains are DNase positive. Strains of S. fonti-cola have been isolated from water samples andreported as Citrobacter-like bacteria with lysinedecarboxylase production (12). Researchershave reported that with commercial identifica-tion systems, S. odorifera may look like atypical(gelatin-positive, anaerogenic) E. aerogenes. S.odorifera strains are nonpigmented and have acharacteristic odor that resembles the smell ofvegetable matter, which is helpful in making acorrect identification. Strains of S. odoriferahave been recovered from clinical specimensand may be clinically significant because of thestrains studied (13).The reasons for the 11 (3.6%) erroneous iden-

tifications (Table 3) were as follows: 3 (27.3%)resulted from reaction discrepancies, 5 (45.4%)displayed aberrant biochemical patterns, and 3(27.3%) required insufficient additional tests. Asshown in Table 4, the three reaction discrepan-cies in the common tests consisted of one false-

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422 ESAIAS, RHODEN, AND SMITH

TABLE 2. Accuracy of identification by the Enteric-Tek system with unknown enteric cultures

Organism No. correct/No. tested % Correct

Proteus vulgarisProteus mirabilis (3)'Morganella morganii (1)Providencia alcalifaciensProvidencia stuartii (3)Providencia rettgeriEdwardsiella tarda (2)Salmonella enteritidisSalmonella, atypical (5)Salmonella paratyphi ASalmonella typhi (1)Salmonella cholerae-suisArizona hinshawii (1)Citrobacter freundiiCitrobacterfreundii, atypical (2)Citrobacter diversusCitrobacter amalonaticus (1)Shigella dysenteriaeShigella flexneriShigella boydiiShigella sonneiEscherichia coliEscherichia coli, H2S positiveEscherichia coli, atypical (10)Yersinia enterocoliticaYersinia pseudotuberculosisKlebsiella pneumoniae (1)Klebsiella oxytocaKlebsiella ozaenaeKlebsiella rhinoschleromatisEnterobacter cloacaeEnterobacter sakazakiiEnterobacter aerogenes (1)Enterobacter gergoviaeEnterobacter agglomeransHafnia alveiSerratia liquefaciensSerratia marcescensSerratia rubideaeSerratia odorifera

9/99/910/1010/1012/128/8

12/129/95/53/43/44/4

11/119/90/210/1014/143/35/52/29/910/105/58/104/53/4

10/1010/106/96/6

10/102/2

10/105/5

10/1010/108/8

11/115/51/1

100.0100.0100.0100.0100.0100.0100.0100.0100.075.075.0

100.0100.0100.0

0.0100.0100.0100.0100.0100.0100.0100.0100.080.080.075.0100.0100.066.6100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0100.0

a Number in parentheses indicates the number of atypical strains tested.

positive adonitol; one false-positive adonitol,lactose, and sorbitol; and one false-positive ly-sine and false-negative sorbitol strain. For threecultures of K. ozaenae, differentiation requiredadditional conventional biochemical tests be-yond the two tests, gas and motility, shown inthe code book. These cultures were incorrectlyidentified by the Enteric-Tek system as Klebsiel-la rhinoschleromatis, the first-choice identifica-tion. K. ozaenae was given as the second choiceon the basis of a negative reaction for gasproduction. The problem might be eliminated byincluding the additional tests, esculin and gasfrom cellobiose, in their data base. A positiveesculin reaction occurs in 75% of K. ozaenaestrains, as compared with 15.4% of K. rhinosch-leromatis strains. A positive reaction with gasfrom cellobiose has been shown to occur in 70%of K. ozaenae strains, whereas all K. rhinosch-

leromatis strains show a negative gas reaction(11).

Five atypical strains with aberrant reactionpatterns were misidentified. The organisms in-volved were two atypical E. coli strains, whichwere indole and lactose negative; two atypicalC. freundii strains (one H2S-negative strain andone H2S-negative indole-positive strain); andone atypical ornithine-positive and H2S-negativeS. typhi strain. The atypical S. typhi strain wasincorrectly identified as S. enteritidis, as is sug-gested by percentage charts supplied by themanufacturer (Flow Laboratories) showing a100% negative ornithine reaction. These chartsalso show a 4% probability for E. coli strains tohave negative indole and lactose reactions and a10% probability for H2S-negative and indole-positive C. freundii strains. Misidentification ofthese atypical E. coli and C. freundii strains by

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EVALUATION OF THE ENTERIC-TEK SYSTEM 423

TABLE 3. Misidentifications of unknown cultures by the Enteric-Tek system

Reason No. % Misidentifications cu Totalcultures

Biochemical reaction discrepancy 3 27.3 1.0Atypical pattern 5 45.4 1.6Insufficient biochemical tests indicated 3 27.3 1.0Total 11 100.0 3.6

the Enteric-Tek system might be eliminated ifthese reactions were included in the data base.Of the 11 misidentifications, 6 were of typical

strains and 5 were of atypical strains (Table 4).Of the 11 misidentifications, 10 required supple-mental tests, including 5 serological confirma-tions for 1 S. paratyphi A and 1 atypical S. typhistrain and Shigella serology for 1 Y. enterocoli-tica and 2 atypical E. coli strains, becauseShigella was listed as first, second, and thirdchoices. The two Salmonella strains, identifiedas S. enteritidis, did not meet expected specieslevel of identification as claimed by the manu-

facturer. However, had these two Salmonellabeen identified only to genus, with subsequentserology required, this would have increased theoverall identification rate to 97.0%. Identifica-tions for the two atypical E. coli strains werelisted as Shigella for all three choices for onestrain and for the first three choices of the otherstrain, with Y. enterocolitica given as a fourthchoice. Shigella serology was required for theone misidentified Y. enterocolitica strain be-cause Shigella was given as the third-choiceidentification.The Y. enterocolitica strain, misidentified by

the Enteric-Tek system as K. rhinoschleromatis,presented an interesting situation. The four iden-tification choices and their probability percent-ages were listed in this order: K. ozaenae

(75.56%), K. rhinoschleromatis (21.19%), S.flexneri (3.06%), and Y. enterocolitica (0.05%).S. flexneri could be eliminated as a possibleidentification, on the basis of serology. We did

the three additional tests-gas, KCN, and raffi-nose-as suggested by the manufacturer, and allthree gave a negative reaction. Since K. ozaenaeshowed a greater probability for positive reac-

tions in all three tests, we eliminated this choiceas a possible identification. On the basis of a

greater probability percentage given for K. rhin-oschleromatis (25.9%), we decided on thischoice instead of Y. enterocolitica (0.05%) as theidentification. The three negative test reactionsfavor the identification as Y. enterocolitica rath-er than K. rhinoschleromatis. This situationillustrates the potential for misidentifying an

organism if the probability percentage given foreach choice identification is the sole criterion.This example emphasizes the need to considerequally all given information and use colonycharacteristics before making an identification.Had the manufacturer suggested a motility testat 25°C, a correct identification would have beenmade. At the time our study was done, we wereunaware that the manufacturer could provideidentification probability percentages based onEnteric-Tek, plus additional tests.K. ozaenae presented the greatest challenge

to the system, with three misidentificationscausing 27.3% of all misidentifications. The re-maining erroneous identifications involved twospecies, with two misidentifications each, andfour species with only one misidentificationeach.The analysis of the 4,228 individual test com-

parisons revealed the Enteric-Tek System to bevery sensitive and specific, showing high test

TABLE 4. Identification errors made by the Enteric-Tek system

Organism Enteric-Tek identification Reason for misidentification

S. paratyphi A (1)' S. enteritidis Lysine positive and sorbitol positivebS. typhi (1)C S. enteritidis Ornithine positive and H2S negativeC. freundii (2)c E. agglomerans H2S negative

E. coli H2S negative and indole positiveE. coli (2)c Y. enterocolitica Indole negative and lactose negative

Unidentified Indole negative and lactose negativeY. enterocolitica (1) K. rhinoschleromatis Adonitol positive bY. pseudotuberculosis (1) K. rhinoschleromatis Adonitol, lactose, and sorbitol positivebK. ozaenae (3) K. rhinoschleromatis (3) Gas and motilityd

a Number in parentheses indicates the number of cultures.b Biochemical reaction discrepancy.c Atypical strain.d Insufficient biochemical test indicated.

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correlations when compared with other rapididentification systems. For comparison, an anal-ysis of the common test reactions for severalrapid systems showed the following results forthe number of tests with a 97% or better agree-ment, when each was compared with the con-ventional counterpart: Enteric-Tek with 10 of 14(71.4%), Micro-ID with 6 of 11 (54.5%), API 20Ewith 6 of 15 (40%), and the Entero-Set 20 systemwith 6 of 16 tests (37.5%) (1, 2). The comparisonshowed that urease, citrate, arabinose, adonitol,and malonate differed substantially in theiragreement percentages. The urease test agree-ment was poorer in the Enteric-Tek (83.4%) andEntero-Set 20 (95%) systems (1-4). The highlysensitive urease test in the Enteric-Tek systemdid not cause any misidentifications, whereasthe urease test in the Micro-ID system hascaused misidentifications because of its lack ofsensitivity and specificity (3). The Enteric-Teksystem performed better in the citrate test with91.4% agreement, as compared with the Entero-Set 20 (86%) and API 20E (83 to 86%) systems(1, 2). The Entero-Set 20 showed poorer agree-ment for two additional tests, adonitol (86%) andmalonate (89%), whereas the Enteric-Tek andMicro-ID each gave similar agreement percent-ages for adonitol (94%) and malonate (99%) (1,2, 4). A low agreement percentage for the arabi-nose test (39 to 82%) in API 20E has beenreported, as compared with 99 to 100% in Enter-ic-Tek, Micro-ID, and Entero-Set 20 (1, 2). Itmust be noted that such comparisons do haveinherent weaknesses, as pointed out by Edberget al. (7).A rapid and accurate identification system for

the Enterobacteriaceae is highly desirable in theclinical laboratory. Such a system would provebeneficial in directing antimicrobic therapy, aswell as increasing identification capabilitieswithout additional demand on trained personnel.We found the Enteric-Tek system to be accurateand easy to use. The advantages included easyinoculation, minimal manipulation, minimalgrowth for sufficient inoculum, useful listings ofsupplemental tests and probability percentages,and easy reading of color changes in the media.The major limitations involved distinguishingbetween weakly positive and negative H2S reac-tions and reading the indole test with weaklypositive strains. Although the Enteric-Tekwheels are stackable, their size and shape mayrequire more storage room, as compared withsome of the other rapid kits.

Overall, we found that the Enteric-Tek systemprovided a highly acceptable level of identifica-tion for the Enterobacteriaceae within 18 to 24 hand served as an alternative procedure to theconventional method. Because this study wasdesigned only to determine the ability of the

Enteric-Tek system to identify the Enterobac-teriaceae, additional testing will be necessary inevaluating its performance in a clinical setting.Since atypical strains present the greatest chal-lenge to the clinical laboratory worker, the needfor subjective evaluation, particularly of colonymorphology, pigment, and odor, remains essen-tial when an unusual organism is encountered.

LITERATURE CITED

1. Aldridge, K. E., B. B. Gardner, S. J. Clark, and J. M.Matsen. 1978. Comparison of Micro-ID, API 20E, andconventional media systems in identification of Entero-bacteriaceae. J. Clin. Microbiol. 7:507-513.

2. Aldridge, K. E., and R. L. Hodges. 1981. Correlationstudies of Entero-Set 20, API 20E, and conventionalmedia systems for Enterobacteriaceae identification. J.Clin. Microbiol. 13:120-125.

3. Barry, A. L., and R. E. Badal. 1979. Rapid identificationof Enterobacteriaceae with the Micro-ID system versusAPI 20E and conventional media. J. Clin. Microbiol.10:293-298.

4. Blazevic, D. J., D. L. MacKay, and N. M. Warwood. 1979.Comparison of Micro-ID and API 20E systems for identi-fication of Enterobacteriaceae. J. Clin. Microbiol. 9:605-608.

5. Brenner, D. J., J. J. Farmer III, F. W. Hickman, M. A.Asbury, and A. G. Steigerwait. 1977. Taxonomic andnomenclature changes in Enterobacteriaceae. Center forDisease Control, Atlanta, Ga.

6. Buesching, W. J., D. L. Rhoden, A. 0. Esaias, P. B.Smith, and J. A. Washington H. 1979. Evaluation of themodified Micro-ID system for identification of Enterobac-teriaceae. J. Clin. Microbiol. 10:454-458.

7. Edberg, S. C., B. Atkinson, C. Chambers, M. H. Moore,L. Palumbo, C. F. Zorzon, and J. M. Singer. 1979. Clini-cal evaluation of the Micro-ID, API 20E, and convention-al media systems for identification of Enterobacteriaceae.J. Clin. Microbiol. 10:161-167.

8. Edwards, P. R., and W. H. Ewing (ed.). 1972. Identifica-tion of Enterobacteriaceae, 3rd ed. Burgess PublishingCo., Minneapolis, Minn.

9. Ewing, W. H. 1975. Differentiation of Enterobacteriaceaeby biochemical reactions-reprinted. Center for DiseaseControl, Atlanta, Ga.

10. Ewing, W. H., and B. R. Davis. 1970. Media and tests fordifferentiation of Enterobacteriaceae. U.S. Departmentof Health, Education and Welfare, National Communica-ble Disease Center, Atlanta, Ga.

11. Flfe, M. A., W. H. Ewing, and B. R. Davis. 1979. Thebiochemical reactions of the tribe Klebsielleae-reprinted.Center for Disease Control, Atlanta, Ga.

12. Gavini, F., C. Ferragut, D. hard, P. A. Trinel, H. Le-Clerc, B. LeFebvre, and D. A. A. Mossel. 1979. Serratiafonticola, a new species from water. Int. J. Syst. Bacter-iol. 29:92-101.

13. Grimont, P. A., F. Grimont, C. Richard, B. R. Davis,A. G. Stelgerwalt, and D. J. Brenner. 1978. Deoxyribonu-cleic acid relatedness between Serratia plymuthica andother Serratia species, with a description of Serratiaodorifera sp. nov. (type strain: ICPB 3995). Int. J. Syst.Bacteriol. 28:453-463.

14. Kelly, M. T., and J. M. Latimer. 1980. Comparison of theAutoMicrobic System with API 20E, Enterotube, Micro-ID, Micro-Media Systems, and conventional methods foridentification of Enterobacteriaceae. J. Clin. Microbiol.12:659-662.

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