JOURNAL OF CLINICAL MICROBIOLOGY, Aug. 1979, p. 161-1670095-1137/79/08-0161/07$02.00/0

Vol. 10, No. 2

Clinical Evaluation of the MICRO-ID, API 20E, andConventional Media Systems for Identification of

EnterobacteriaceaeSTEPHEN C. EDBERG,* BEVERLY ATKINSON, CAROL CHAMBERS, M. HELEN MOORE, LUCY

PALUMBO, CORINE F. ZORZON, AND JACQUES M. SINGER

Division ofMicrobiology, Department ofPathology, Montefiore Hospital and Medical Center, The AlbertEinstein College ofMedicine, New York, New York 10467

Received for publication 16 May 1979

MICRO-ID (General Diagnostics, Morris Plains, N.J.) is a new kit systemdesigned for the identification of Enterobacteriaceae in 4 h. It consists of 15biochemical tests of paper disks. Each test is in its own compartment in a moldedplastic tray. Only one reagent need be added to the system (2 drops of 20% KOH,which is added to the Voges-Proskauer test). Based on the pattern of positive andnegative biochemical test results, a five-digit octal code number is calculated. Anidentification is derived from a computer-generated identification manual. Astudy was conducted to compare three systems-the MICRO-ID 4-h and the API20E (Analytab Products Inc., Plainview, N.Y.) 18- to 24-h systems and a conven-tional media system-to measure the ability of each to identify members of thefamily Enterobacteriaceae. Comparison tables, rather than simple percentageagreement tables, were generated to define the particular strengths and weak-nesses of each system and allow the laboratory to best use the data. The MICRO-ID compared quite favorably with conventional media. MICRO-ID yielded incor-rect identifications with 1.5% of the isolates tested (API 20E, 4.7% misidentifica-tion rate). Half the MICRO-ID misidentifications occurred when the systemidentified a Citrobacter diversus as a lysine-negative Escherichia coli; all gaveone octal number. A direct comparison of the MICRO-ID and API 20E was oflimited value because percentage agreements were merely the sums of the errorsof each. The ease of inoculation, the requirement for the addition of only onereagent, and the 4-h capability make the MICRO-ID system an extremelyattractive development in the field of bacterial identification.

Reagent-impregnated paper strips have beenused for many years for the rapid identificationof Enterobacteriaceae (7). The MICRO-ID is asecond-generation reagent-impregnated paperdisk system containing 15 biochemical reactionsin a molded plastic tray with a hinged cover(Fig. 1). The unit is designed for the 4-h identi-fication of Enterobacteriaceae from a primaryisolation medium. The biochemical tests, eachin its own compartment, are: Voges-Proskauer,reduction of nitrate, deamination of phenylala-nine, hydrogen sulfide production, indole pro-duction, decarboxylation of ornithine and lysine,malonate utilization, urea, esculin hydrolysis, o-nitrophenyl-fi-D-galactopyranoside hydrolysis,and sugar fermentation tests for arabinose,adonitol, inositol, and sorbitol. Each compart-ment contains both the substrate and the indi-cator. MICRO-ID differs from other commer-cially available products in that only one reagentis added to the system (2 drops of 20% KOH to

the Voges-Proskauer compartment) and resultsare available after 4 h of incubation. No reactionneed be overlaid with oil, and each compartmentreceives 0.2 ml of inoculum equal to or greaterthan a 0.5 MacFarland turbidity standard.

Positive and negative reactions are dividedinto five groups of three tests each, and a five-digit number, or octal code, is generated fromthe test results. Accompanying the product is acomputer-generated identification manual thatprovides the name of the most likely species; theLFR (likelihood fraction), a value that allowsone to calculate how closely the test patternobserved with the unknown resembles the pat-tern most likely to be produced by each of thespecies; and another value, the PNOR (normal-ized probability), which allows one to determinethe best choice of species by calculating howwell each species is separated from the others.The manual also indicates the quality of anidentification and specific additional tests, if re-

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162 EDBERG ET AL.

MiCROD): -.:~~~~~~~~~~~~a

,-t , -N;:-<-:' -'4 ¢ i.'. .~~~~~~~~~~~~~~o

FIG. 1. MICRO-ID contains 15 biochemical reactions on paper-impregnated disks. Each biochemical testis in its own compartment in a hard plastic tray. The first 5 tests on the left have a substrate disk and adetection disk; after incubation, the MICRO-ID is tilted to wet the upper disks. Only one reagent, 2 drops of20%o KOH to the Voges-Proskauer (VP) reaction, is added to the system. N, Nitrate reduction; PD, phenylal-anine deamination; H2S, H2S production; I, indole production; OD, ornithine decarboxylation; LD, lysinedecarboxylation; M, malonate utilization; U, urea; E, esculin hydrolysis; ONPG, o-nitrophenyl-/-D -galacto-pyranoside hydrolysis; ARAB, arabinose fermentation; ADON, adonitol fermentation; INOS, inositol fer-mentation; SORB, sorbitol fermentation.

quired.The API 20E system, made for the 18- to 24-

h identification of enteric bacteria, is well de-scribed in the literature (6, 8) and has become acommonly used commercial system for the iden-tification of Enterobacteriaceae. AnalytabProducts Inc. (Plainview, N.Y.) provided a com-puter-based identification manual that yieldsthe likelihoods of identifications from numeri-cally calculated biotype numbers. Both the MI-CRO-ID and the API manuals are based on datagenerated in the field.A study was undertaken to compare three

systems: the 24-h MICRO-ID, the 24-h API 20E,and a conventional media system based on theCenter for Disease Control (CDC) biochemicalseries (3, 4).

(This work was presented in part at the 78thAnnual Meeting of the American Society forMicrobiology, Las Vegas, Nev. [S. C. Edberg, B.Atkinson, C. Chambers, H. Moore, C. Zorzon,and J. M. Singer, Abstr. Annu. Meet. Am. Soc.Microbiol. 1978, C167, p. 305].)

MATERIALS AND METHODSBacterial strains. A total of 768 fresh clinical

isolates were obtained from the Microbiology andImmunology Laboratory, Montefiore Hospital andMedical Center, the Albert Einstein College of Medi-cine (New York, N.Y.). All clinical cultures were se-quential isolates from the routine service laboratoryexcept that colonies consistent with Escherichia coli,by morphology, were excluded after 100 strains wereencountered in order to avoid a preponderance of thisspecies in the data. Ten stock cultures were from thesame source, and additional strains were from the Cityof New York Department of Health (courtesy of Y.Fauer).Conventional identification. Enterobacteria-

ceae were identified according to procedures described

by the CDC (4, 5). Conventional tests routinely usedincluded: triple sugar iron agar, indole production,deoxyribonuclease, esculin hydrolysis, decarboxyla-tion of ornithine and lysine, deamination of phenylal-anine, hydrolysis of o-nitrophenyl-,B-D-galactopyrano-side, motility, utilization of citrate and malonate, fer-mentation of sorbitol, and production of cytochromec oxidase. When necessary, appropriate serological andadditional biochemical tests were performed. Duringthe course of this investigation the taxonomic nomen-clature of Edwards and Ewing (4, 5) rather than thatof Bergey's Manual ofDeterminativ,e Bacteriology (3)was used. Recently, changes in taxonomy have beenrecommended by the CDC (2). Whereas some of thesechanges were simply of nomenclature, others involvedbiochemical tests that were not used during the courseof this study. Where the Edwards and Ewing taxon-omy (4, 5) and the new CDC nomenclature (2) yieldthe same genus and species names based on the bio-chemical battery used in this study, we so indicate(Table 1).MICRO-ID. For the MICRO-ID, directions sup-

plied by the manufacturer were followed. All reactionswere read after 4 h of incubation, and a five-digit octalnumber was calculated. Using the MICRO-ID com-puter identification manual (September 1978 edition),the isolate was given one of the following five desig-nations: (i) identified to genus and species, (ii) identi-fied to genus level only, (iii) two or more choices aspossible identifications ("not separated"), (iv) octalcode not in the computer identification manual, or (v)misidentified.API 20E. For the API 20E, directions for Entero-

bacteriaceae supplied by the manufacturer were fol-lowed except that before inoculation each isolate wastested for its ability to produce cytochrome c oxidase.The API strips were incubated for 20 to 24 h, and abiotype number was calculated. Using the API 20Eprofile index (April 1978 edition), each isolate wasassigned one of the following five designations: (i)identified to genus and species, (ii) identified to thegenus level only, (iii) two or more choices as possibleidentification ("not separated"), (iv) biotype number

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EVALUATION OF THREE IDENTIFICATION SYSTEMS 163

TABLE 1. Number of isolates and stock culturesstudied in the evaluationa

No.Name Clinical Stock

isolates cultures

Escherichia coli 157 0Shigella species 4 0Shigella sonnei 3 0Edwardsiella tarda 0 1Salmonella typhi 0 1Salmonella enteritidis 20 3Arizona hinshawii 0 2Citrobacter freundii 34 1Citrobacter diversus 26 0Klebsiella pneumoniae 140 0Klebsiella ozaenae 15 0Enterobacter aerogenes 25 0Enterobacter cloacae 53 0Enterobacter hafniae 15 0Enterobacter agglomerans 9 0Serratia marcescens 29 0Serratia liquefaciens 8 0Proteus vulgaris 17 0Proteus mirabilis 113 0Proteus morganii 60 0Proteus rettgeri 12 0Providencia alcalifaciens 2 0Providencia stuartii 26 0Yersinia enterocolitica 0 2

a Conventional identifications were made accordingto Edwards and Ewing (4) and Ewing (5). Accordingto recent CDC nomenclature (2) and based on thebiochemical tests performed in this study, the follow-ing names are interchangeable: K. pneumoniae, indolepositive (K. oxytoca), E. hafniae (Hafnia alvei), andP. morganii (Morganella morganii). One of the 12 P.rettgeri corresponded to P. stuartii, urea positive; theremaining 11 corresponded to P. rettgeri. Enterobac-ter sakazakii and Enterobacter gergoviae, if isolated,would be considered E. aerogenes, and C. amalona-ticus would correspond to C. freundii.

not in the profile index, or (v) misidentified.Procedure. After isolation on a primary plate, each

isolate was restreaked once to insure purity and thenidentified by each of the three systems at the sametime. The study was divided among bacteriology tech-nologists. There was no correlation between errors ineither system and the people who did the work. Toclosely parallel the actual clinical state, isolates weretested in each kit system once.

Evaluation. We chose to present the data fromthis study in a somewhat different form from thatpreviously used in clinical microbiology. An in-housecomputer program (in collaboration with M. Feuer,Data Processing, Montefiore Hospital and MedicalCenter) was written so that the data derived from thethree different identification systems could be easilycompared. The resultant chart, which we call a com-parison table, allows the display of all data in ourstudy. The tables are constructed so that, in a uniformmanner that does not require the reader to follow an

often complex flow chart, system A can be comparedwith system B, A compared with C, and B comparedwith C. The strains identified from system A (theconventional system) are listed vertically, along witha column showing the total number of each speciesidentified by system A. Horizontally, the names de-rived from system B (the MICRO-ID) are listed. Thetable is utilized in much the same way as a mileagechart to determine the distance between cities is used.For example, Table 2 shows that 157 E. coli isolateswere identified by the conventional system; from theE. coli row on the horizontal axis it is seen that theMICRO-ID identified 154 (98.1%) of these as E. coliand 3 (1.9%) as "not separated." The dashes in thetable refer to combinations that are not encounteredand are used rather than zeroes to facilitate the user'sorientation in space and to allow the eye to effortlesslytravel horizontally and vertically on the table. To'determine what the conventional biochemical seriesnamed an isolate when the MICRO-ID called it E.coli, one finds E. coli on the horizontal MICRO-IDaxis and, following the column down the vertical axis,finds that of the 161 E. coli identified by MICRO-ID,154 (95.7%) were E. coli, 1 was Citrobacter freundii,and 6 (3.7%) were C. diversus by the conventionalsystem. The conduct of each of the strains studiedcan, therefore, be presented in one table. Likewise,Table 3 presents the results ofsystem A (conventional)versus those of system C (API 20E), and Table 4presents the results of system B (MICRO-ID) versusthose of system C (API 20E). The comparison tables,therefore, allow a more direct visualization of areas ofdisagreement between multiple systems than do thetraditional tables that vertically list results.

RESULTS

Tables 2, 3, and 4 show comparisons of thethree tested systems. The tables were designedto show the name of an isolate in one systemversus the name(s) of the isolate in each othersystem. In this way all isolates used in the studywere presented. Percentages of general agree-ment between the three systems were also cal-culated.

After 4 h of incubation, MICRO-ID and con-ventional procedures (Table 2) agreed on thegenus and species name of an isolate in 719 of778 cases (92.4%). In 26 cases (3.3%) MICRO-IDyielded a "not separated" answer (two or morechoices possible). The correct genera and specieswere listed among the choices in 25 of these 26cases. The MICRO-ID identification manualprovided a series of biochemical reactions toseparate the choices. Using the recommendedtests, the correct genus and species names werederived in all 25 cases. In one case (0.1%) anoctal number could not be found in the MICRO-ID identification manual. This isolate was cor-rectly identified from an extended computermanual by calling the MICRO-ID customer ser-vice telephone number. Overall, therefore, the

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164 EDBERG ET AL.

TABLE 2. Comparison of conventional and MICRO-ID identifications of isolates"'MICRO-ID IDENTIFICATION

z

0

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(Lz

z

z

0

C>

0

--I

" This and Tables 3 and 4 are used in much the same way as standard mileage charts are used for determiningthe distance between cities. For example, if one wished to determine the MICRO-ID efficacy for the identificationof K. pneumoniae, one would determine, from the "conventional identification" column, that 140 strains weretested. Following a parallel line to the "MICRO-ID identification" column, one would find that the MICRO-IDidentified 138 of these as K. pneumoniae, 1 as "not in book," and 1 as "not separated." -, Combination notencountered, or 0.

MICRO-ID system correctly identified to thegenus and species level 743 of 778 isolates(95.5%). In 20 cases (2.6%) the MICRO-ID pro-vided only genus identifications. In all 20 casesthe correct genera were identified. MICRO-ID

supplied incorrect identifications in 12 of 778cases (1.5%). The major discrepancy betweenthe conventional battery and the MICRO-IDsystem occurred when the MICRO-ID identified6 C. diversus isolates as lysine-negative E. colistrains (Table 2). All 6 misidentifications yieldedone octal number, 23031.

After 20 to 24 h of incubation, the API 20Eand conventional systems (Table 3) agreed onthe genus and species name of an isolate in 706of 778 cases (90.7%). In 29 cases (3.7%) the API20E yielded biotype numbers that were notfound in the profile index. All 29 biotype num-bers were checked with the API computer ser-vices. Eleven isolates of the 29 were correctlyidentified to genus and species, 8 yielded one ormore choices possible with low selectivity, and10 were misidentified. Of these 8 cases in which

one or more choices were listed as possible iden-tifications, the correct choice was present 6times. The computer service provided sufficientdiscriminating biochemical tests to differentiatethese 6. Including the diagnoses provided by theAPI computer services, the API 20E correctlyidentified 721 of 778 isolates (92.7%). In 2 casesthe API 20E yielded biotype numbers with oneor more species as possible answers. In bothcases the correct species was listed, togetherwith a series of biochemical reactions to identifythe correct choice. In 18 cases (2.3%) the API20E provided correct genus identifications butno species identifications. In all 18 cases thecorrect genera were identified. Of these 18 cases,12 occurred when the system called a C. diversusa Citrobacter species. In 23 of 778 cases (3.0%)the API provided incorrect identifications. In-cluding the 12 misidentifications provided by theAPI computer services from the 29 isolates "notin book," the overall misidentification rate was4.5%. Overall, therefore, the API 20E providedthe correct genus and species identifications 723

Ecol' 157 15.4 - - -3

Shigella sp 4 4

S sonne 3 3 - -

E tarda - -

S typh' 11 - - - -

S enter'todis 23 3 -

A 11nfShaw 2 2 -2

C freuind, 35 33 _

C diversus 26 6 - 13 7

K pneumoniae 140 - 138 - -- - 11K ozaenae 15 14

E aerogenes 25 25

E cloacae 53 -44 99

E hafnae 15 15

E agglomerans 9 7 2

S marcescens 29 - 26 2

S lIquelaciens 8 7 1

P vulgaris 17 - - 15 2 -

P mirabIl,s 113 1107 5 -

P morganti 60 -- - - 2 56- -

P rettgert 12 -8 4- 4 -

P alcallacens 2 1 1

P stuarl? 26.-- 20 6

Y enterocoltica 2 _ L_L_ L _ - -L __2 -_ L _

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EVALUATION OF THREE IDENTIFICATION SYSTEMS 165

TABLE 3. Comparison of conventional and API 20E identifications of isolates"API 20E IDENTIFICATION

11 bQ

If, 'IC'4T ()/ lk-' -k-/ / 144' CO" C-2 q. Al

"See footnote to Table 2.

of 778 times (92.9%).The MICRO-ID and the API 20E agreed on

the genus and species names of isolates in 667 of778 cases (85.7%) (Table 4). This figure has greatpractical importance for the practicing clinicalmicrobiologist, because it demonstrates the po-tential danger of comparing one commercial sys-tem directly with another without a proven ref-erence system available to act as the arbitrator.An isolate misidentified, identified to genus only,or not separated (one or more choices as possibleidentifi'cation) could not be expected to agreewith the genus and species name derived fromthe second system. The 14% disagreement isclose to the sum of the genus and species disa-greements derived from each system.

DISCUSSIONBoth the MICRO-ID and the API 20E iden-

tified members of the family Enterobacteria-ceae with a high degree of accuracy (Tables 2and 3). We chose to analyze the data in a formwhich not only presents the identification of allstrains used in the study but also does not re-

quire the additional explicative tables. Thesetables can easily be used to evaluate one productas compared with another. Whereas percent

agreement figures are general reflections of theoverall accuracy of a system, they do not ade-

quately reflect the particular strengths andweaknesses of each system tested and often re-

quire additional explanatory materials. Compar-ison tables present results which clearly show allthe data and do not require lengthy commen-

tary. With this information a laboratory can

optimally utilize a given system and, with a

knowledge of the areas of discrepancy between

the multiple systems, will exercise more cautionin reporting results from these areas.

Any clinical evaluation can be flavored by the

mix of isolates used, the personnel assigned, and

the method of data analysis. We chose to analyzethe data in the form presented because the per-cent agreement figures are very much a function

of the mix of isolates used in the study and maynot adequately reflect the strengths and weak-

ness of each system. For example, if there had

been an overrepresentation of C. diversus, the

MICRO-ID percentage of agreement would

have suffered; if there had been an overrepresen-tation of Serratia liquefaciens and/or C. diver-

sus, the API 20E percentage of agreement with

the conventional method would have suffered.

Based on colonial morphology, some selections

z

0

LL

zLUC]

z0

zLU

z

0

E coOi 157153-----------------------1 3

Shigella sp 4 - 4 -

S sonneu 3 _ 2

E tarda 1 - - ------ - -

S typho I 231

Sentertids 23 - - 22- -- -- ------- -

A hlnshawis 2- 2 _- -

C freund,, 35-------32 ------------- 3

C d,versus 26-------1 7- - ---12 -6-K pneumonae 140---------138 -----------------2 -

K ozaenae 15---------4 11---------- --

E aerogenes 25-----------2311------- -1I -

E cloacae 53 -- - - - - - --48 - - -- -- - - - 4

E hafn,ae 15------------ -14-------------- 1-E agglomerans 9-------2------6 ---------- 1

S marcescens 29- 23 1-- 3 -

SIlquefaciens 87 3- 3-|-2

Pvulgarts 17 -- - 13- - -3 -

P mirabtils 113 -1093.-- 1--19P morgant 60-- -1-157---------- - 115

P rettger, 12- 8 - 4 - - - - -

P alcaktaciens 2 2 ----2

P stuar,ti 26---- - 226

Y enterocohl,ca 2 -- ------ - -- - -- - -- 2-

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166 EDBERG ET AL.

TABLE 4. Comparison ofMICRO-ID and API 20E identifications of isolatesa

MICRO-ID IDENTIFICATION

45 1 ~~~~~~~~~~~~~4 a~~~~- QIii48 / r j1A4

1,~c I C I It It, c c5 Q q q

" See footnote to Table 2.

of specimens were made to prevent overrepre-

sentation by the most commonly encounteredspecies. Since more than 85% of strains isolatedin our routine laboratory are E. coli, Klebsiellapneumoniae, or Proteus mirabilis, the overall

percentage of agreement of any kit with conven-

tional procedures will be significantly affected ifthe kit showed a particular ability to identify or

misidentify any of these species. Comparisontables allow a rapid means of determining wherea system errs while permitting the user to cal-culate percent agreements for each species.

It was felt that fresh clinical isolates wouldmore closely mimic the performance of a systemin the clinical setting than would stock cultures.Bacteria after storage or multiple transfers invitro may undergo dissociation and lose R-fac-tors. Because the MICRO-ID measures consti-tutive enzymes, it is possible that on storagesome or all members of the Enterobacteriaceaemay turn down or turn off enzyme systems,

resulting in negative or weak reactions, whereasfresh isolates may produce a positive reaction.In its instructions to users, the manufacturer ofMICRO-ID recommends that the inoculum den-sity for stock cultures be four times that of freshisolates.

To evaluate commercial systems on the mostequitable basis while at the same time maintain-ing conditions as close to actual usage as possi-ble, the personnel chosen for the study were

experienced laboratory technologists who per-

formed the evaluation in parallel with their nor-

mal workload. To insure a steady, unhurriedgeneration of data, no technologist performedmore than five evaluation cultures per day.Table 4 shows that the comparison of a new

test procedure with other than a standard ref-erence procedure carries with it an inherenterror. Errors in the comparison approximate thesums of the errors of each of the systems tested.The low general rate of agreement (85%) be-tween the MICRO-ID and the API 20E is a

demonstration of this concept. Each test systemestablishes its own data base founded on its ownbiochemical formulations, test series chosen, andmeans to handle the data. Because the biochem-ical test formulations may not be the same in alltest kits, and no kit uses medium formulationsexactly the same as those used by the CDC, a

direct comparison of biochemical tests in one

system with those of any other system, includinga conventional one, is nonproductive. If, for ex-

ample, a hypothetical kit were able to detect

z

0

LL

z

EL

Total number 161 4 3 1 1 23 2 33 14 139 14 25 44 15 7 26 7 16 109 56 8 1 20 2 0 12 7 1of strains

Ecoh 153150- - -

Shigella sp 4 4 --------;

S sonne ~

E tarda -1

S typhi - -

S enteritidis 22 22 - -

A hinshawii 2 - 2 _-C freundi, 35 2 30 1 22 _ _

C dversus 7 --- -- - --4 - - - - - -

K pneumoniae 142 - - - - - 137 3_- - - - -

K ozaenae 11 - - -- 11_- - -

E aerogenes 27 -23 3 1 2 _E cioacae 50 1 39 - - - -E hafn,ae 14 -. -14E agglomerans 6 - 4S marcescens 23 -20-----20SlIquefaciens 4 - - - - - 1 3P vulgaris 14 - 13 - - -

P mirabldls 110 - 11104 1 4P morgani 60 - _ 4 53 2P rettgeri 8 _ -- 7P a/calhfaciens 2 - --P stuarttic 30 - - - - - - 20 3 6Y enterocolitica 2 - - - - 2Citrobacter sp 14 3 - -6 0Proteus sp 2Provodencla sp 0 - - - - - 0O -Serratia sp 2 - - - 2 0Not in book 29 6 1 3 3 2 4 1 1 3 - 2 1 - 0Not separated 2 2 _

26

3

9

22

4

0

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EVALUATION OF THREE IDENTIFICATION SYSTEMS 167

H2S production by Enterobacter cloacae butnot other Enterobacter species, the kit could usethis characteristic to differentiate E. cloacaeeven though the H2S reaction is considered false-positive compared with the conventional test.This hypothetical example demonstrates theneed each identification system has for its owndata base. Computer-generated identificationmanuals, which usually accompany kits, provideselections based on patterns of positive and neg-ative results derived from the kits, not fromconventional tests. The manual may also pro-vide a measure of probability, as in the case ofthe API 20E and MICRO-ID, and a likelihoodfraction, as with MICRO-ID, both of which as-sist the user in "fine-tuning" the answer. Errorsin identification can be solely a function of thecomputer-generated manual, even with a correctbiochemical test series. The identification of anisolate should, of course, be correct, but errorsof identification will be unique to the test sys-tem. Therefore, each system tends to have itsstrengths and weaknesses, and, when comparingone against the other directly, a low order ofagreement is achieved because the errors of bothare summed.

In our hands, the new MICRO-ID system isaccurate and, in terms of the common criteria ofacceptance, easily exceeds the 95% agreementlevel with conventional methodology. It appearsthat changes in the computer identification man-ual have improved the level of identificationfrom the first edition of the manual (1). The ease

of inoculation, the requirement for the additionof only one reagent, and the 4-h capability makeit an extremely attractive development in thefield of bacterial identification.

LITERATURE CIMD1. 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 Enter-obacteriaceae. J. Clin. Microbiol. 7:507-513.

2. Brenner, D. J., J. J. Farmer, F. W. Hickman, M. A.Asbury, and A. G. Steigerwalt. 1977. Taxonomic andnomenclature changes in Enterobacteriaceae. Depart-ment of Health, Education and Welfare publ. no. (CDC)78-8356. Center for Disease Control, Atlanta.

3. Cowan, S. T. 1974. Family I. ENTEROBACTERIA-CEAE RAHN 1937, 281 Nom. gen. cons. Opin. 15, Jud.Comm. 1958, 73, p. 290-340. In R. E. Buchanan and N.E. Gibbons (ed.), Bergey's manual of determinativebacteriology, 8th ed. The Williams & Wilkins Co., Bal-timore.

4. Edwards, P. R., and W. H. Ewing. (ed.). 1972. Identi-fication of Enterobacteriaceae, 3rd ed. Burgess Publish-ing Co., Minneapolis.

5. Ewing, W. H. 1973. Differentiation of Enterobacteria-ceae by biochemical reactions, revised. Department ofHealth, Education and Welfare publ. no. (CDC) 74-8270. Center for Disease Control, Atlanta.

6. Nord, C. E., A. A. Lindberg, and A. Dahlback. 1974.Evaluation of five test kits-API, Auxotab, Enterotube,PathoTec, and r/b-for identification of Enterobacte-riaceae. Med. Microbiol. Immunol. 159:211-220.

7. Smith, P. B., D. L. Rhoden, and K. M. Tomfohrde.1975. Evaluation of the Pathotec Rapid I-D System foridentification of Enterobacteriaceae. J. Clin. Microbiol.1:359-362.

8. Smith, P. B., K. M. Tomfohrde, D. L Rhoden, and A.Balows. 1972. API system: a multitube micromethodfor identification of Enterobacteriaceae. Appl. Micro-biol. 24:449-452.

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