Evaluation of the Enteric Tek system for identifying Enterobacteriaceae

0095-1137/82/030419-06$02.00/0

Evaluation of

the Enteric-Tek

System

for

Identifying

Enterobacteriaceae

A.0. ESAIAS,*D. L. RHODEN,ANDP. B. SMITH

Centerfor Infectious Diseases, Centers for Disease Control, Atlanta, Georgia 30333

Received 26 June 1981/Accepted 5 October 1981

TheEnteric-Tekwheel(Flow Laboratories), consistingof 14 different

biochem-ical parameters for rapidly identifying Enterobacteriaceae, was evaluated and

compared with the conventional method for completely identifying 301 enteric cultures, representing 36 species. The Enteric-Tek system correctly identified 264

(97.8%) of the270 common ortypicalstrains and 26

(83.9%)

of the 31 unusual or

atypical strains tested, demonstrating an overall identification accuracy rate of

96.3%. There were 80 (26.6%) correctly identified strains requiring additional

tests.Ofthe 11 (3.6%) misidentifications,5(3Klebsiella and 2Salmonellastrains)

were correctly identified atthe genus level. When 4,228 individual tests in the

Enteric-Tek wheel were compared with theconventional tubedmedia, 96.4% of

thetestsagreed;urease, citrate,

adonitol,

and lactose agreedless than97%. The

Enteric-Teksystem wasfoundtobe reliableand accurate inproducing

identifica-tions atthegenus and species level within 18to 24 h.

Sinceasubstantialproportion of the workload

generated in the clinical

microbiology

laboratory

involvesisolating and

identifying

Enterobacteri-aceae, the development ofrapid identification

systems for enteric bacteria has increased, as

evidenced by thenumerouscommercially

avail-able kits (2, 14). Many of these systems have

beenstudied and evaluatedby various

investiga-tors. A new commercial identification system,

theEnteric-Tek wheel (Flow Laboratories,

Ros-lyn, N.Y.), is designed to identify the

Entero-bacteriaceae at the genus and species level

within18 to 24hof isolationonprimary plating

media. By the use of 14 different biochemical

parameters, the system generates a five-digit

octal

profile

number derived from the

biochemi-calreactions. In ourstudy,

interpretation

of the

reactions was made according to the

manufac-turer's recommendations so an identification

could be derived fromthe computercode book.

The purpose of this evaluation was to

deter-mine the ability of the Enteric-Tek system to

identify both typical and atypical members of

Enterobacteriaceae. This study presents data

whichdescribethe performance and accuracy of

the Enteric-Tekwheel as compared with a

con-ventional identification system.

MATERIALS AND METHODS

Bacterial culturestested.Wetested 301 of ourstock cultures from the General Bacteriology Laboratory, Centers for Disease Control, culture collection. These cultures had been assigned code numbers by a third party. The selectedcultures,welldistributedamong 36 species, 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 storedat rodmtemperaturein thedark. Each culture had previ-ously been identified by conventional procedures (5, 8-11). Theidentityof each culture remainedunknown

until all results were compiled and the testing was

completed.

Conventionalmethod foridentification. Eachculture was streaked onto a MacConkey agar plate and a blood agar plate. Cultures were then identified by conventional biochemicaltests(5, 8-10). The conven-tionaltestsroutinelyperformed included reactionson

triple sugar iron agar (H2S production); Christensen

urea 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, inosidulci-tol, adonidulci-tol, mannidulci-tol, sucrose, salicin, arabinose, raffinose, and rhamnose. These mediawere

inoculated from culture suspensions in tryptone broth and were incubated at 35C. After 18 to 24 h of incubation, reagents were added for indole, methyl red, VP (acetoin), and phenylalanine tests. Tests which were not positive within 18 to 24 h were observed foramaximum of7 days. When required, additionaltests wereperformed to complete the identi-fication, e.g., growthin KCNandserological confir-mation ofSalmonella andShigella. Allcultureswere identified by the nomenclature and taxonomy de-scribedby Edwards and Ewing (8, 9)andBrenneret

al.(5). When necessary, the Enterobacteriology Sec-tion, CDC,wasconsulted as areference laboratory.

Enteric-Tek system. The Enteric-Tek system is a round, multicompartment wheel, consisting of a

cen-tral well and 11 individual peripheral wells, all of which contain solid media. The system provides for

419

on February 7, 2020 by guest

http://jcm.asm.org/

determining 14 different biochemical parameters which include: indole production; tryptophan deami-nase; H2S production; citrate; malonate; lysine and ornithine decarboxylase; urease; and acid production from glucose, lactose, rhamnose, adonitol, sorbitol, and arabinose. All organisms tested were inoculated onto MacConkey agar and blood agar plates and incubated for 18 to 24 h at 35°C. A suspension from several well-isolated colonies of each organism was made in2ml of sterile distilled water. Before inocula-tion, the wheels were allowed to warm to room temperature and were labeled appropriately. Inocula-tion was done as described in the detailed instrucInocula-tions provided by the manufacturer. Each wheel was placed in an upright position, incubated at 35°C for 18 to 24 h, then removed from the incubator, and observed for color changesin the solid media. The only manipula-tion required to observe a biochemical reacmanipula-tion in-volved rolling a cotton swab saturated with a special indole reagent (Flow Laboratories) over growth in the

centerwell. Any redness developing within 30 s indi-cated apositive indole reaction. The remainder of the wells were visually observed, and their color was read, assuggestedby the manufacturer. All reactions were recorded on a printed formand tabulated into a five-digit profile number for identifying organisms listed in the manufacturer's code book. The data incorporated into the computer code book were generated from the percentagecharts of Edwards andEwing (8) and from in-housestudies.Identification was based on the prob-ability that asetof biochemical reactions would occur with more likelihood for one particular organism than for another and allowed for thepossibility ofatypical reactions. The code book listsadditional biochemical testsrequired tocompleteanidentification. The addi-tionaltestsinclude:arginine,cellobiose, DNase,

escu-lin, gas from glucose, inositol, Jordan tartrate,

potassi-umcyanide, maltose, mannitol,methyl red, motility,

raffinose, VP, xylose,andserologyforSalmonella and

Shigella.

RESULTS

Agreement of tests. Biochemical reactions for

the varioustestsin the Enteric-Teksystemwere

compared with those obtained

by

the

conven-tional method. Of the 14 common tests, 10

showed more than 97% agreement with their

conventional counterparts, whereas urease,

ci-trate,

adonitol,

and lactose

agreed 83.4, 91.4,

94.0, and94.4%, respectively.

Thesefourtests comprised 75% ofall of the

testdiscrepancies. Certain groups of

organisms

wereresponsible for

lowering

theagreement for

some of the tests. The 50 differences in the

ureasetest, all

false-positive

in the Enteric-Tek

systemexcept for

1,

occurred with 6 Citrobacter

freundii, 10Citrobacter

diversus,

14Citrobacter

amalonaticus,4Klebsiellapneumoniae, 4

Kleb-siella oxytoca, 8Enterobacter

cloacae,

1

Hafnia

alvei, 1

Morganella

morganii, and 1 Yersinia

enterocolitica strain. OneProteusrettgeristrain

gave a

false-negative

reaction

despite

a4+

reac-tion in the convenreac-tional Christensen urea agar

slant. The 26citratetest

discrepancies

included

22false-negatives and 4false-positives butwere

not responsible for any misidentifications. Of

the 18differences in the adonitol test, all of the

11 strains ofSerratia marcescens, 1 Serratia

liquefaciens, 1 K.pneumoniae, 1 Shigella

flex-neri, 2 Yersinia pseudotuberculosis, and 1 Y.

enterocolitica strain were false-positive, but

only2ofthe latter3culturesweremisidentified.

One false-negative adonitol reaction occurred

with a Providencia alcalifaciens strain. The 17

discrepancies in lactose were divided almost

equallybetween thefalse-negative(9) and

false-positive(8)reactions. Differencesin the lactose

resultsdidnotchangetheidentifications.

Identification. Overall, the Enteric-Tek

sys-temcorrectlyidentified, at the genus and species

level, 96.3% of the 301 strains tested. As shown

in Table 1, the system correctly identified 264

(97.8%) of the typical strains and 26 (83.9%) of

theatypical strains. Of the 290 cultures correctly

identified, 62of 270 typical strains (23.0%) and

18 of 31 atypical strains (58.1%) required

addi-tional tests. The number of additional tests

rangedfrom one test for 7 strains, two tests for

42strains, andthree tests for 30 strains, to five

tests for 1 atypical Escherichia coli strain. We

performed the suggested additional tests when

an identification was given with less than 95%

probability. Although correct identifications for

one Arizona hinshawii, one S. flexneri, two

Shigella boydii, and one Y. enterocolitica were

listed as first-choice identifications, serological

confirmation was required because the given

probabilities were less than 95%. Twenty-one

strains required serological confirmation

be-cause theassignedidentifications were listed as

second, third, and fourth choices in the code

book.

The identification accuracy of individual

spe-cies by the Enteric-Tek system is shown in

Table 2. Thesystemprovided 252 (86.9%) of the

correctidentifications asthe first choice. There

were38identifications listedassecond, third,or

fourth choices(29assecond, 6 asthird,and3 as

fourth). The Enteric-Tek system correctly

iden-tified 100% of the strains for 29 of 36 species

(80.6%)tested. The number of strains tested for

eachspecies rangedfrom2to 14, except for 25

E. colistrains,which included

H2S-positive

and

atypicalstrains. Twoatypicalstrains of both E.

coli and C.freundiiweremisidentified,

decreas-ingtheiridentificationratesfrom100%to92 and

82%, respectively. Four strains each of

Salmo-nella paratyphi A, Salmonella

typhi,

and Y.

enterocolitica were tested; one strain of each

wasmisidentified, resulting in a75%

identifica-tion rate for each

species.

The misidentified

strainofS. typhiwasatypical. Both Salmonella

strains wereidentifiedasS.

enteritidis,

listedas

thesecond choice in the manufacturer's

comput-J. CLIN. MICROBIOL.

on February 7, 2020 by guest

http://jcm.asm.org/

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

Organism_Organismcategory_categoryNo._{No. tested}tested No. correct No. correct requiring

_{~~~~~~~~~~~~~~additional}

_tests'

Common ortypical 270 264(97.8)b 62(23.0)c

Unusual oratypical 31 26(83.9) 18(58.1)

Total 301 290(96.3) 80(26.6)

aIncluding

Salmonella

andShigellaserologywhenrequired.

b Number inparenthesesgivesthepercentage for thecategory.

cNumber inparenthesesindicates the percentage of the numbercorrectin thecategory.

er code book. Klebsiella ozaenae, with nine

strainstested, showed the lowest identification

rate(66.6%), because three strains did notmeet

the expected species level ofidentification, as

claimedby the manufacturer.

DISCUSSION

In comparison with the conventional

meth-ods, the Enteric-Tek system demonstrated a

highly acceptable level of

identification

accura-cyfor the 301 stock cultures tested. The overall

identification

rate of the Enteric-Tek system

(96.3%)

compares

favorably

with the

Micro-media' System

(97%)

and Entero-Set 20

(96%)

andis better than the Micro-ID

(94%),

API20E

(92%),

and Enterotube

(84%)

systems when

each system is compared with conventional

methods (2, 14). Another

study

reported

a

higher

identification rate

(97%)

for both the API 20E

and Micro-ID systems (3).

Thirty-six

enteric

speciesweretested with the Enteric-Tek

wheel,

as

compared

with21to28enteric

species

tested

with the otherrapid identification kits. For

iden-tifying

a

large

variety

of enteric bacterial strains to the

species level,

the Enteric-Tek system

shows potential

advantages

over some of the

rapidsystemspreviously evaluated(2-4, 6, 14).

The Enteric-Tek system can correctly identify

Serratia strains as to species, whereas the API

20E system has frequently been reported to

identify them at the genus level only (4, 14).

Additionally, atest for adonitol fermentation is

included in this system, asinthe Micro-IDand

Entero-Set 20but notinAPI 20E, allowingfor

the differentiation of H2S-negative C. freundii

fromC.diversus withouttheneed for additional

tests (4). Unlike the Micro-ID data base, the

Enteric-Tek system includes identification for

Enterobacter gergoviae and C. amalonaticus

strains (6).

Additionalspecies of variedlevelsofdifficulty

were used in this study, and the Enteric-Tek

systemcorrectlyidentifiedallstrains for 29 of 36

species(81%)tested. By comparison, 20 enteric

species were tested against the following rapid

systems, with the indicated number of species

havingalloftheirstrainscorrectlyidentified:the

Micro-Media system with 17

(85%),

Micro-ID

with 13 (65%), Enterotube with 12 (60%), and

API 20E with 11 (55%) (14). The scope ofthe

Enteric-Tek systemdatabase wasdemonstrated

bythe 185differentprofile numbers generatedin

derivingtheidentifications, witha rangeof1to9

different profile codes for each species tested.

The Enteric-Tek system showed the ability to

identify two new Serratia species, S. fonticola

andS.odorifera. This abilitywasclearlyshown

when the one S. odorifera strain tested was

correctly identified as a first-choice

identifica-tion, havinga 87.71%

probability.

Also, with 8

of 10 correctly identified Enterobacter

aero-genes strains, the Enteric-Tek system listed S.

fonticola,E. aerogenes, and S.odorifera,inthat

order,asfirst-, 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%)

andS.odorifera(0.02%). In both of these

situa-tions,twoadditionaltests, VP andDNase,were

suggested by the manufacturertoeasily

differen-tiate these species. All S. fonticola strains are

listed asVPnegative, whereas allE. aerogenes

strains are VP positive. All strains for both S.

fonticola and E.aerogenes have beenshownto

be DNase negative, whereas all S. odorifera

strainsare DNase positive. Strains ofS.

fonti-cola have beenisolated fromwatersamples and

reportedasCitrobacter-like bacteria with lysine

decarboxylase production (12). Researchers

have reported that with commercial

identifica-tionsystems,S.odorifera maylook like atypical

(gelatin-positive,

anaerogenic)E. aerogenes. S.

odorifera strains are nonpigmented and have a

characteristic odor that resembles the smell of

vegetable matter, which is helpful in making a

correct identification. Strains of S. odorifera

have been recovered from clinical specimens

andmay beclinically significant because ofthe

strainsstudied (13).

Thereasonsforthe 11 (3.6%) erroneous

iden-tifications (Table 3) were as follows: 3 (27.3%)

resulted fromreaction discrepancies, 5 (45.4%)

displayed aberrant biochemical patterns, and 3

(27.3%)

required insufficient additionaltests. As

shown inTable4, the three reaction

discrepan-cies in thecommon testsconsistedofone

false-VOL. 15, 1982

on February 7, 2020 by guest

http://jcm.asm.org/

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

Organism No.correct/No. tested %Correct

Proteusvulgaris Proteusmirabilis (3)' Morganella morganii (1) Providenciaalcalifaciens Providenciastuartii (3) Providenciarettgeri Edwardsiella tarda (2) Salmonella enteritidis Salmonella, atypical (5) Salmonella paratyphiA

Salmonella typhi (1) Salmonella cholerae-suis Arizonahinshawii (1) Citrobacterfreundii

Citrobacterfreundii, atypical (2) Citrobacterdiversus

Citrobacter amalonaticus (1)

Shigella dysenteriae

Shigellaflexneri

Shigella boydii Shigella sonnei Escherichia coli

Escherichia coli, H2S positive Escherichiacoli, atypical (10)

Yersiniaenterocolitica Yersiniapseudotuberculosis Klebsiella pneumoniae (1) Klebsiella oxytoca Klebsiella ozaenae

Klebsiella rhinoschleromatis Enterobacter cloacae Enterobactersakazakii Enterobacter aerogenes (1) Enterobacter gergoviae Enterobacteragglomerans Hafnia alvei

Serratialiquefaciens

Serratiamarcescens

Serratiarubideae Serratiaodorifera

9/9 9/9 10/10 10/10 12/12 8/8 12/12

9/9 5/5 3/4 3/4 4/4 11/11

9/9 0/2 10/10 14/14 3/3 5/5 2/2 9/9 10/10

5/5 8/10 4/5 3/4 10/10 10/10 6/9 6/6 10/10

2/2 10/10

5/5 10/10 10/10 8/8 11/11

5/5 1/1

100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

75.0 75.0

100.0 100.0 100.0 0.0 100.0 100.0 100.0 100.0

100.0

100.0

100.0

100.0

80.0 80.0 75.0

100.0

100.0 66.6

100.0

100.0

100.0

100.0

100.0 100.0 100.0

100.0 100.0

100.0

100.0

aNumber inparentheses indicates the number ofatypicalstrains tested.

positive adonitol; one false-positive adonitol,

lactose, andsorbitol; and one false-positive

ly-sine andfalse-negative sorbitol strain. Forthree

cultures ofK. ozaenae, differentiation

required

additional conventional biochemical tests

be-yond the twotests, gas and motility, shown in

the code book. Thesecultures wereincorrectly

identifiedbytheEnteric-Teksystem as

Klebsiel-la rhinoschleromatis,the first-choice

identifica-tion.K.ozaenae wasgivenas thesecondchoice

on the basis of a negative reaction for gas

production.Theproblemmightbeeliminatedby

including the additional tests, esculin and gas

from cellobiose, in their data base. A positive

esculin reaction occurs in 75% of K. ozaenae

strains, ascomparedwith15.4%of K.

rhinosch-leromatis strains. A positive reaction with gas

from cellobiosehas been shown to occur in70%

ofK. ozaenae

strains,

whereas allK.

rhinosch-leromatis strains show a

negative

gas reaction

(11).

Five

atypical

strains with aberrant reaction

patterns were misidentified. The

organisms

in-volvedwere twoatypical E. colistrains, which

were indole and lactose

negative;

two

atypical

C.

freundii

strains(one

H2S-negative

strainand one

H2S-negative indole-positive

strain);

and

oneatypical

ornithine-positive

and

H2S-negative

S. typhi strain. The atypical S.

typhi

strain was

incorrectly identifiedasS.

enteritidis,

asis

sug-gested by percentage charts

supplied by

the

manufacturer (Flow

Laboratories)

showing

a

100% negative ornithine reaction. These charts

also show a4%

probability

forE.colistrains to

havenegative indoleand lactosereactions anda

10% probability for

H2S-negative

and

indole-positiveC.

freundii

strains. Misidentification of

theseatypical E. coli and C. freundii strainsby

on February 7, 2020 by guest

http://jcm.asm.org/

423

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

Reason No. %Misidentifications cu_cultures

Total

Biochemical reactiondiscrepancy 3 27.3 1.0

Atypical pattern 5 45.4 1.6

Insufficientbiochemicaltestsindicated 3 27.3 1.0

Total 11 100.0 3.6

the Enteric-Tek system might be eliminated if

these reactionswere included in the database.

Of the11 misidentifications, 6wereoftypical

strains and 5 wereofatypicalstrains(Table 4).

Of the 11misidentifications, 10required

supple-mental tests, including 5 serological

confirma-tionsfor 1 S.paratyphiAand 1 atypicalS.typhi

strain andShigella serology for1 Y.

enterocoli-tica and 2 atypical E. coli strains, because

Shigella was listed as first, second, and third

choices. Thetwo Salmonella strains, identified

asS. enteritidis, did not meetexpected species

level of identification as claimed by the

manu-facturer. However, had these two Salmonella

been identified only to genus, with subsequent

serology required,thiswouldhaveincreasedthe

overall identification rate to 97.0%.

Identifica-tions for the two atypical E. coli strains were

listed as Shigella for all three choices for one

strain and for the first three choices oftheother

strain, with Y. enterocolitica given as a fourth

choice. Shigella serology was required for the

one misidentified Y. enterocolitica strain

be-cause Shigella was given as the third-choice

identification.

The Y. enterocolitica strain, misidentifiedby

theEnteric-TeksystemasK.rhinoschleromatis,

presentedaninteresting 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 possible

identification, on the basis ofserology. We did

the three additionaltests-gas, KCN, and

raffi-nose-assuggestedbythemanufacturer,andall

threegave anegative reaction.Since K.ozaenae

showed agreater probability for positive

reac-tions in all threetests,weeliminatedthis choice

as a possible identification. On the basis ofa

greaterprobabilitypercentage given for K.

rhin-oschleromatis (25.9%), we decided on this

choice instead ofY.enterocolitica(0.05%)asthe

identification. The three negative testreactions

favorthe identificationas Y.enterocolitica

rath-er than K. rhinoschleromatis. This situation

illustrates the potential for misidentifying an

organism if theprobabilitypercentagegiven for

each choice identification is the sole criterion.

This example emphasizes the need toconsider

equally all given information and use colony

characteristics before making an identification.

Had the manufacturersuggested amotility test

at25°C,acorrectidentification would have been

made. At the timeourstudywasdone,we were

unaware that the manufacturer could provide

identification probability percentages based on

Enteric-Tek, plus additionaltests.

K. ozaenae presented the greatest challenge to the system, with three misidentifications

causing 27.3% ofallmisidentifications. The

re-maining erroneous identifications involved two

species, with two misidentifications each, and

four species with only one misidentification

each.

Theanalysis of the 4,228 individualtest

com-parisons revealed the Enteric-Tek Systemtobe

very sensitive and specific, showing high test

TABLE 4. Identification errors made by theEnteric-Tek system

Organism Enteric-Tek identification Reason formisidentification

S.paratyphiA(1)' S. enteritidis Lysine positive and sorbitolpositiveb

S.typhi(1)C S.enteritidis Ornithine positive and H2S negative

C.freundii (2)c E.agglomerans H2S negative

E.coli H2Snegative and indole positive

E.coli (2)c Y.enterocolitica Indole negative and lactose negative Unidentified Indole negative and lactose negative

Y.enterocolitica (1) K. rhinoschleromatis Adonitol positiveb

Y.pseudotuberculosis (1) K. rhinoschleromatis Adonitol, lactose, and sorbitol positiveb

K.ozaenae (3) K.rhinoschleromatis (3) Gas andmotilityd

aNumber in parentheses indicates the number of cultures.

bBiochemicalreaction discrepancy.

cAtypical strain.

dInsufficient biochemical test indicated.

VOL.15, 1982

on February 7, 2020 by guest

http://jcm.asm.org/

correlations when compared with other rapid

identificationsystems. For comparison, an

anal-ysis of the common test reactions for several

rapid systems showed the following results for

thenumber 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 with6of11 (54.5%), API 20E

with6of15(40%),and the Entero-Set 20 system

with6 of 16 tests(37.5%)(1, 2). The comparison

showed thaturease,citrate,arabinose, adonitol,

and malonate differed substantially in their

agreement percentages. The urease test

agree-ment was poorerin the Enteric-Tek(83.4%)and

Entero-Set 20 (95%) systems (1-4). The highly

sensitive urease testin the Enteric-Tek system

did not cause any misidentifications, whereas

the urease test in the Micro-ID system has

caused misidentifications because of its lack of

sensitivity and specificity (3). The Enteric-Tek

systemperformed better inthecitrate test with

91.4%agreement, ascomparedwiththe

Entero-Set 20(86%) and API20E (83 to 86%) systems

(1, 2). The Entero-Set20 showed poorer

agree-mentfortwoadditional tests,adonitol(86%)and

malonate (89%), whereas the Enteric-Tek and

Micro-ID eachgavesimilar agreement

percent-agesfor adonitol(94%) and malonate(99%) (1,

2, 4). Alowagreementpercentageforthe

arabi-nose test (39 to 82%) in API 20E has been

reported,ascomparedwith99 to100% in

Enter-ic-Tek, Micro-ID, and Entero-Set 20 (1, 2). It

must be noted that such comparisons do have

inherent weaknesses, aspointedoutby Edberg

etal. (7).

A

rapid

andaccurateidentificationsystemfor

theEnterobacteriaceae is

highly

desirable in the

clinicallaboratory. Such a systemwould prove

beneficial in directing antimicrobic therapy, as

well as increasing identification capabilities

without additional demandontrainedpersonnel.

Wefound theEnteric-Teksystemtobeaccurate

andeasy to use. The

advantages

included easy

inoculation, minimal

manipulation,

minimal

growth forsufficient

inoculum,

useful

listings

of

supplementaltestsand

probability

percentages,

and easyreading of color changes inthe media.

The major limitations involved

distinguishing

betweenweakly

positive

and

negative

H2S

reac-tions and reading the indole test with weakly

positive

strains. Although the Enteric-Tek

wheels are stackable, their size and shape may

require more storage room, as

compared

with

someof the otherrapidkits.

Overall,wefoundthatthe Enteric-Tek system

provided ahighly acceptablelevel of

identifica-tion fortheEnterobacteriaceaewithin 18to24 h

and served as an alternative

procedure

to the

conventional method. Because this

study

was

designed only to determine the

ability

of the

Enteric-Tek system to identify the Enterobac-teriaceae, additional testing will be necessary in

evaluating its performance in a clinical setting.

Since atypical strains present thegreatest

chal-lengetothe clinicallaboratoryworker, the need

for subjective evaluation, particularlyof colony

morphology, pigment, and odor, remains

essen-tialwhen an unusualorganismis encountered.

LITERATURE CITED

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

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

3. Barry,A.L.,andR. E. Badal.1979.Rapid identification of Enterobacteriaceae with the Micro-ID system versus API 20E and conventional media. J. Clin. Microbiol. 10:293-298.

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

5. Brenner, D. J., J. J. FarmerIII,F. W.Hickman,M. A.

Asbury, and A. G. Steigerwait. 1977. Taxonomic and nomenclaturechanges in Enterobacteriaceae. Center for Disease Control, Atlanta, Ga.

6.Buesching, W.J., D. L. Rhoden, A.0. Esaias, P. B. Smith, and J.A.Washington H. 1979. Evaluation of the modifiedMicro-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,andJ. M.Singer.1979. Clini-calevaluationof theMicro-ID,API 20E, and convention-almedia systems for identification of Enterobacteriaceae. J.Clin. Microbiol. 10:161-167.

8. Edwards, P.R., andW.H.Ewing(ed.). 1972. Identifica-tion ofEnterobacteriaceae, 3rd ed. Burgess Publishing Co.,Minneapolis,Minn.

9. Ewing,W. H.1975.Differentiation of Enterobacteriaceae by biochemical reactions-reprinted. Center for Disease Control, Atlanta, Ga.

10. Ewing,W.H.,and B. R.Davis. 1970.Media andtestsfor differentiation of Enterobacteriaceae. U.S. Department ofHealth,Education andWelfare,National Communica-ble DiseaseCenter,Atlanta,Ga.

11. Flfe,M.A.,W.H.Ewing, and B. R. Davis. 1979. The

biochemical reactions of the tribeKlebsielleae-reprinted. Center for DiseaseControl, Atlanta,Ga.

12. Gavini, F., C. Ferragut, D.hard, P. A. Trinel,H.

Le-Clerc,B.LeFebvre,and D. A. A. Mossel. 1979. Serratia fonticola,a newspeciesfromwater.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-cleicacid relatedness between Serratia plymuthicaand other Serratia species, with a description of Serratia odoriferasp.nov.(typestrain: ICPB3995).Int. J.Syst. Bacteriol. 28:453-463.

14. Kelly,M.T.,andJ.M. Latimer.1980.Comparisonof the

AutoMicrobicSystemwith API20E,Enterotube, Micro-ID, Micro-MediaSystems,andconventional methods for identification of Enterobacteriaceae. J. Clin. Microbiol. 12:659-662.

on February 7, 2020 by guest

http://jcm.asm.org/