Comparison of the API 20E and Oxi/Ferm systems in identification of nonfermentative and oxidase positive fermentative bacteria

0095-1 137/79/02-0220/07$02.00/0

Comparison

of the API 20E and

Oxi/Ferm Systems in

Identification

of Nonfermentative and Oxidase-Positive

Fermentative

Bacteria

THOMAS R. OBERHOFER

MicrobiologySection, Departmentof Pathology, MadiganArmy MedicalCenter, Tacoma, Washington 98431

Received forpublication 2September1978

The API20E andOxi/Fermsystems weretestedinparalleltoidentify nonfer-mentativebacteria andoxidase-positive fermentativebacteria. Test strains con-sisted of consecutive clinical isolates, with stock cultures used to supplement thosespecies infrequentlyrecovered. The twomicrosystems, aswell as tubes of triplesugariron, motility, cetrimide,and oxidativeglucose media, were inoculated by each worker for each organism. Identification of each isolate was by the protocol of the manufacturers, with supplemental tests andflagella stains per-formedwhen necessary.Concurrent identificationwasundertaken witha

conven-tional system againstwhich the results of the two systems were compared for accuracy. There was a 95.3% accuracy inidentification bytheOxi/Fermsystem and88.9% by the API system. Almost one-fourth of all identification attempts with theAPIrequiredcomputerassistance,andmostof thesewerefor oxidase-positive bacteria. Because ofthis, and because the API system showed greater accuracy in identification of theoxidase-negative bacteria,it seems best suited for identification of these organisms (P. maltophilia, A. anitratus, and A. lwoffi). The Oxi/Ferm system istechnically lesscumbersome than the API and is well suited for both groups oforganisms.

The isolation and identification of nonfer-mentative bacteria (NFB) have come to be an essential taskinthe clinicalmicrobiology labo-ratory, especiallyasworkers come to recognize theirpresence andimportanceaspotential path-ogens.Eventhough various schema for identifi-cation of theNFB areavailableinthe literature (2, 5, 7, 8), it isclearthat there is a needfor less complicatedsystems that will offer an alterna-tive tothemoreconventionalmethods currently in use.

Few proven miniaturized systems are availa-ble commercially tofacilitate the identification of NFB and the oxidase-positive fermentative bacteria (OPFB). One of these, the Oxi/Ferm (OxF)system (Roche Diagnostic Division, Hoff-man-LaRoche, Inc., Nutley, N.J.), has been eval-uatedwithfresh clinical isolates (3) as well as a large variety of stock cultures of known identity (6). Recently, the OxF and API (Analytab Prod-ucts Inc., Plainview, N.Y.) systems were com-pared for usefulness in identifying both the fer-mentative and nonferfer-mentative, oxidase-posi-tivebacteria (1, 4).

Thisreport presents the results of a compar-ativestudy of both the API and OxF systems to

identifyfreshclinical isolates of NFB and OPFB.

Each system wasevaluatedforperformanceand accuracy of identification when tests were per-formed concurrently under similar conditions. Also, the recently revised API profile register wascomparedtothe manualformerlyinusefor ease ofuse, ability todecode, and accuracy of organism identification.

(Thispaper waspresentedinpartatthe78th Annual Meeting of the American Society for Microbiology,LasVegas, Nev.,14-19May 1978.)

MATERIALS AND METHODS

Organismstested. The287fresh clinicalisolates tested in this studywererecovered and identifiedover a 14-month period inthe Microbiology Laboratory, Madigan Army Medical Center. Onlythose cultures judgedtobe ofclinicalimportance wereselected for testing. Eleven additional strains (three strains each of FlavobacteriumIIb,CDCVE-2,and Achromobac-ter xylosoxidans and one each of CDC IIk-2 and Flavobacterium Iflwere stockorganismswhichwere selected to supplement the infrequently recovered clinicalisolates.

Commercial systems-general approach. By ourprocedures, non-lactose-fermenting organisms as seen on MacConkey agar or organisms growing on bloodagaronlywereroutinelyscreened with the oxi-dase test. Alloxidase-positive organisms were tested directlywith both the API and OxF systems. Oxidase-220

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COMPARISON OF API 20E AND OXI/FERM SYSTEMS 221 negative NFB were tested in one of two ways.

Expe-rienced technologists, suspecting NFB based on the

colonial morphology of the isolates on blood or

MacConkeyagarplates,inoculatedboth the API and OxFsystems.Techniciansoflesserexpertise generally

inoculated API strips only, with theOxF system in-oculated later when an NFB was noted. Stock

orga-nismsweregiven tovarious workers as unknowns and

processedassimulated clinicalspecimensaspart of an

internal qualitycontrolprogram.The following media wereroutinelyinoculatedinparallelto the two test

systems: a triple sugar iron slant for fermentation

reactions; an oxidation-fermentation glucose tube

without oiloverlayforglucoseoxidation,accompanied

by a tube ofbasal medium;atube ofsemisolid medium

formotilitydeterminations;and acetrimideslant for tolerance testing. Later, acetamide (5) was added to the battery of tests. Allsystems and media were

in-cubatedat35°C.Additional tests necessary for proper

identificationwere used assuggestedin therespective

codemanuals.

API system. Well-isolated colonies were harvested andemulsified in saline and used toinoculatethewells of the API 20E test strip. Afterovernight incubation,

positive results were recorded on the worksheet. If

glucosewasacidified,orif three testsexceptingoxidase werepositive,reagents were added and the tests were

interpretedaccording to themanufacturer's directions.

Tests not meeting theseconditionswerereincubated

for anadditional24h.Reactionsagain wererecorded, and, regardless of the number ofpositive results at thistime, the reagents were added to the strips and the results were coded. Isolates which could not be

identifiedbecause of failure of themanualstocontain

thespecificcodes werereferred to the computer ref-erence centerforidentification.Therevised code

man-ual, dated October 1977 and received in December 1977 (hereafterreferred to as revised), was used to identify thoseorganismswhichhad been coded pre-viously with the manual in use at the time of testing

(hereafter referredto asformer). Isolates tested after

receiptof therevised manualwereidentifiedbyusing

bothmanuals.

OxFsystem. Thedetailsofinoculationand

inter-pretation oftestreactions have beenpresented else-where (6). Briefly, portions of colonies selected for testing weregatheredontheinoculating needle,and theneedle wasdrawnthrough thecompartments of thetube in asingle twistingmotionand then usedto inoculateaTrypticasesoyagarplate.Afterovernight incubation, the platesand ancillarymedia were re-movedandexamined.TheOxF tubewasexaminedat 48h,withalltestreactionsrecordedatthistime. The indole testwasperformedaccordingtothe

manufac-turer'sdirections, and thetestfor nitriteproduction

wasperformedaspreviously described(6).The result-antcodeswere searched in the code book and addi-tional testswereperformedasnecessary.

Conventional system. The conventional tests usedtoidentifythe NFB and OPFB have been de-scribed(5).Eachbatteryofconventionaltests wasset upduringthesametimeperiodasthetwo

microsys-tems.Identificationsresultingfrom conventionaltests wereconsideredascorrectinall instances.

RESULTS

A total of 298

organisms

was tested during

thisstudy period.When theclinical isolatesare

listed

indescendingorder offrequencyof recov-eryfrom clinical materials (Tables4and5), it is seenthatof the16namedand 9unnamed species listednonpigmented Pseudomonas

aeruginosa

and A. anitratus accounted for 27 and 23% of the strains tested,respectively.Just fivespecies of NFB (P. aeruginosa, A. anitratus, Pseudo-monas maltophilia, Acinetobacter Iwoffi, and Pseudomonas putida) accountedfor 76% of the organisms tested.Conversely,the ninestrainsof

OPFBrecovered duringthestudyperiod

consti-tuted only 3% of the total

organisms

encoun-tered.

The accuracy of thetwosystemsfor identifi-cation of NFB and OPFB is showninTable 1. Whencomparedto conventionalteststhe OxF system correctly identified 284 (95.3%) ofthe strains tested.

Thirteen

species (149 strains) were 100% correct in identification and ac-counted for 50% of the strains tested. Afurther 104strains (35%)were at least 96%correct. Eight strains ofFlavobacterium

llb

and nine of M.

osloensiswereidentifiedtothe genuslevel and

wereconsidered tobecorrectlyidentifiedeven

though the OxF code manual did not accom-modate these species or group designations. Threeisolates of P. acidovorans, on the other hand,were notidentified because the code man-ual didnotdifferentiate thispseudomonadfrom others showing theidentical code.

Of the298cultures tested with the APIsystem

(Table 1), 266

(89.3%)

werecorrectly identified

based on information contained in the

former

code manual. Sixspecies(70 strains)were 100% correctin identification and accounted for 23% of the strains tested. An additional 149 strains

(50%)

were atleast 90%correct.

Overall

results

were similar when the revised code wasused,

althoughidentificationof P.putidaincreased in accuracyfrom83to95% whereas that of Pseu-domonasfluorescens decreasedfrom57to29%.

Additional tests were often necessary for

properidentificationwithboth systems, and the

organisms

relying

on such tests are shown in Table2. Almost half ofidentification attempts with OxFnecessitatedfurthertesting,which far exceeded the requirements for API. It is seen that the fluorescent

pseudomonads

accounted

for 103 ofthe 121 isolates needingthese tests.

Fifty-one P. aeruginosa isolates

required

ce-trimide fordifferentiation

(from

Achromobacter sp.), 21 requiredtests for

growth

at

420C,

and

two

required

both tests. The 20 isolates ofP.

putida required tests for

growth

at

420C

and

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OxF API

No.of Formera Revised

Organism strains No. of

tested strains iden- %Identi- No of No. of

tified fld strains iden-

flIedti

strains iden- Idni

tified fied tified fied

P.aeruginosa 78 77 99 76 97 75 96

P. putida 23 20 87 19 83 22 96

P.fluorescens 7 7 100 4 57 2 29

A.anitratus 65 65 100 64 98 64 98

A.Iwoffi 23 23 100 23 100 23 100

P.maltophilia 28 27 96 28 100 28 100

P.cepacia 10 10 100 9 90 9 90

M.osloensis 9 9 100 9 100 8 89

Moraxellasp. 7 3 43 6 86 6 86

Flavobacterium IIb 8 8 100 6 75 6 75

FlavobacteriumIlf 3 3 100 2 67 2 67

CDCVe 7 7 100 7 100 7 100

CDCIIk 6 6 100 3 50 3 50

P.acidovorans 3 0 0 0 0 0 0

Alcaligenessp. 3 3 100 2 67 2 67

A.xylosoxidans 5 5 100 2 40 2 40

CDCVa 3 2 67 0 0 0 0

P.stutzeri 1 1 100 1 100 1 100

P.multocida 7 6 86 3 43 3 43

A.hydrophila 2 2 100 2 100 2 100

Total 298 284 95.3 266 89.3 265 88.9

a

Former

manual,

December1976;revised

manual,

October1977.

TABLE 2. Supplemental information requiredforidentificationwiththe API and OxF systems No. of strainsidentifiedby API No. of strains No. ofstrsins

Organism tested identifiedby Additionaltests Computer assisted

tested OxF

Former Revised Former Revised

P.aeruginosa 78 75 11 17 12 11

P.putida 23 20 20 22 11 1

A.anitratus 65 0 2 2 13 13

Moraxellasp. 16 12 0 0 1 7

P.fluorescens 7 6 2 4 0 0

P.cepacia 10 0 2 1 7 4

P.maltophilia 28 1 3 3 6 4

A.Iwoffi 23 0 1 1 3 4

FlavobacteriumIIb 8 1 1 0 3 1

CDCVe 7 0 2 1 3 3

A.xylosoxidans 5 0 2 4 2 0

CDCIIk 6 0 2 2 2 2

P.acidovorans 3 3 3 3 0 2

FlavobacteriumIIf 3 0 0 0 2 0

Alcaligenessp. 3 1 2 3 2 2

P.multocida 7 1 0 0 6 6

A.hydrophila 2 1 0 0 0 0

CDC Va 3 0 0 0 1 1

P.stutzeri 1 0 0 0 0 0

Total 298 121 53 63 74 61

(41)a (18) (21) (25) (20)

aNumbersinparenthesesindicate percents.

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COMPARISON OF API 20E AND OXI/FERM SYSTEMS 223

gelatin liquefaction, whereas strains of P.

fluo-rescens needed these as well as several other

tests.Theidentification of the moraxellaerelied

upontests foranaerobic growth in addition to testsforpenicillin susceptibility. Flagella stains were required for differentiation of Pseudo-monassp.and Alcaligenessp.Thetestfor

mo-tility was often necessary as a discriminating

factorbetween A. anitratus, A. lwoffi, and P. maltophilia, but this was not charged against theOxFsystembecause thetestformotility,as

used in this laboratory, constitutes anintegral

partofabasic batteryoftests.The APIsystem, although relying lessonsupplementaltestsfor identification, nevertheless presented unique difficulties. Tests forgrowth at420Cwere still

required for P. aeruginosa (10 and 15 isolates whenusing the respective manuals). Moreover, the P. putida were coded as P. fluorescens

"group," requiring lengthy searches throughthe tables of the former manual for appropriatetests to perform. The use ofthe revised manual as wellas computerassistance resulted in the

fol-lowing tests necessary for identification of P. putida: gelatinase, four strains; lecithinase, three strains; growth at 42°C and gelatinase, five strains;growthat420Candutilization of

aceta-mide, three strains; and growth at 420C and lecithinase, sevenstrains. InadditiontoP. aci-dovorans and the alcaligenes species, A. xy-losoxidansrequired the flagella stainfor iden-tificationwhenusingthe formermanual. When using the revisedmanual, moreover, cetrimide andacetamidealsowereneeded.

Also shown in Table 2 arerequirements for

assistance ofthe computerreference centerfor identification attemptswith the API system. It is seen that computer assistance was heavily relied upon since 25% (74 determinations) and 20%(61 determinations)of theteststrainscould notbeidentified with the informationprovided intherespectivemanuals. Ofparticularinterest

werethefindingsthat 11 of the 19isolates ofP.

putidaand 7 of the 9 isolates ofP.cepaciathat

werecorrectlyidentifiedrequiredcomputer

as-sistance. The revised manual permitted

im-proved perfornancewithP. aeruginosa,P.

pu-tida,and P. cepacia isolates,butreversedthis

trend with themoraxellaisolates.

Table 3 shows thesourcesofdiscrepanciesin

identification.Ten of themisidentificationswith

OxFwere atthe species level,andfourwereat

thegenuslevel. Identificationof P. acidovorans

was incomplete because the manual failed to codeatthespecieslevelfornonoxidative

pseu-domonads.Ofthe 33 cultures misidentifiedwith the API system, 12 were misidentified as to

genus, and 21 were misidentified asto species.

One isolate(Flavobacterium IIb)had an

unac-ceptablecode even withassistance of the

com-puterreference center.

Table 4 shows the number of code profiles generated by API and OxF. Of the 298 cultures tested, there were 153resultant codes with API incontrast to 63 with OxF. Of the more

numer-ousorganismstested, P.aeruginosa had 36

pro-files with API in contrast to 14 with OxF, A. anitratus had 20 (API) and 5 (OxF), and P. maltophilia had 17 (API) and 3 (OxF).

The OxFtest systems wereallexamined after, and the results were recorded after, 48 h of incubation (Table 5). By contrast, 39% of the API tests were recorded at 24 h, with the re-mainder recorded at 48 h. Of the two most commonorganisms tested, results for 65% (42 P. aeruginosa and 51 A. anitratus) were recorded at 24 h. However, of the 10 least encountered species and groups (44isolates), only two results wererecorded at 24 h.

DISCUSSION

Thereliability of theindividual reactions has beendescribed for the API (1, 4) and the OxF (6) systems, so thatinterest during this study wasdirected towards the accuracy and conven-ience of the two microsystems when used

con-currently byworkers ofvarying experience. The

individual test reactions of the two systems are

important

forproperidentification of each iso-late, although aberrant reactions were consid-ered in both code systems. The results of

bio-chemical tests of OxF components have been

described in detail (6), although correlations

with conventional media in the present study

were not as close. Because no codes required computerassistanceforarbitrationand because

thedegreeof accuracy ofidentificationwasquite

high,thedisagreement in test reactionswas not

significant. The reasons that the 14 isolates

could not be identifiedwere varied. The

misi-dentification of the threemoraxellastrainswas

not aresult of poor

performance

but in the code itself. Thatis, the

yellow-pigmented

moraxella-like M4Fand M-6 bacilliweremisidentified as members ofCDC Ik because the code didnot accountfor theseunusual

organisms.

Similarly,

themisidentifiedP.maltophiliawasanunusual

oxidase-positive isolate and hence was not

ac-commodatedintheOxFprofile register.

The testreactionsinAPI wereevaluatedby

Nord et al. (4) and Dowda (1) and found to

compare favorablywiththe conventional tests.

Thisreportdoes notincludeaclosescrutinyof

thebiochemicalindexes becauseit isdifficultto

compare results oftestsofdifferent

composition.

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TABLE 3. Identification ofdiscrepancies between themicrosystemsandconventional tests MisidentificationsbyAPI Organism Misidentificationsby OxF

Former Revised

P.putida 3P.fluorescens 3P.fluorescens 1P.fluorescens 1P.aeruginosa

P.fluorescens 1P.putida 2P.aeruginosa

1Pseudomonas sp. 3P.putida 1P.aeruginosa

P.aeruginosa 1P.putida 2A.xylosoxidans 2P.fluorescens 1P.stutzeri P. acidovorans 3Pseudomonas sp. 2Pseudomonas sp. 2Pseudomonas sp.

1Alcaligenessp. 1Alcaligenessp.

CDC Va 1P.vesicularis 1 P.stutzeri 1 P. stutzeri

1P.cepacia 1 P.cepacia 1Pseudomonas sp. 1Pseudomonas sp.

P.multocida 1P.ureae 4Pasteurella sp. 1CDCIIj

3Pasteurella sp.

Moraxella M-4f 3CDCIIk, 1 1CDCIf 1CDCIf

P.maltophilia 1Pseudomonas sp. Moraxella M-6 1CDCIIk

FlavobacteriumIIb 1CDC IIj 1CDCIIj

1Unacceptable code 1Unacceptablecode

CDC

Ilk,2

3CDC IIk-1 2CDCIIk-1

1Pasteurella sp.

CDCIVc 1Achromobacter sp. 1Achromobacter sp.

1CDC IIj 1CDCIIj

A.xylosoxidans 3Alcaligenes sp. 3Alcaligenes sp.

P.cepacia 1P.stutzeri 1P.stutzeri

M.osloensis 1Pseudomonas sp.

A.anitratus 1Flavobacterium sp. 1Flavobacterium sp.

Total 14 32 33

TABLE 4. Number o, the

Organism

P.aeruginosa A.anitratus P.maltophilia

A.Iwoffi P.putida

Moraxellasp.

P.cepacia

Flavobacterium lIb P.fluorescens CDC Ve P.multocida A.xylosoxidans

CDCIIk

Flavobacterium lIf CDC Va

Alcaligenessp.

P.acidovorans A.hydrophila

P.stutzeri

Total

Thesubstratesuse

ficiently different f to preclude a vali4

fprofiles resulting from use of therewas a60% disagreementin ureasereactions microsystems between API and conventional tests with P. No.of No. of pro- No. of pro- aeruginosaand28%disagreementwith A. ani-strains filesfrom filesfrom tratus.Therewasafurther 76%disagreementin tested API OxF glucoseoxidationfor P.aeruginosabetween the 78 36 14 twotestsystems. To declare that API reactions

65 20 5 wereerroneous would not only beunwarranted

28 17 3 andimproper, butinsupportableaslong as

var-23 9 2 iablereactionswereaccountedfor inthe

key

or 16 5 1 codingsystems. Nevertheless, one testreaction

10 6 4 was particularly troublesome in API and did

8 8 4 account formisidentifications.The test for

nitro-7 6 3 gengaswas

properly

scoredas

positive

whengas

7 7 2 (bubbles) was evident in the glucose

compart-5 2 2 ment or when, after adding zinc dust to a test

6 4 3 negativefor nitrites, a pink or red color

failed

to

3 3 2 appear after 10 min. On many attempts, how-3 3 2 ever,the zinc test failed to give theproper

infor-3 3 2 mation,thereby resulting ineither a

misidenti-2 2 2

fication,

anunacceptablecode, or no code atall. 1 1 1 This wasparticularlytrue for twoisolates each 298 153 63 ofP.fluorescensandFlavobacterium IIbaswell

asanassortment of othercultures.

The overall agreement in identificationwith

,d in theAPIsystemare suf- conventional methods was 99 and 96% at the Fromconventional substrates genus level, and 95 and 89% at thespecies level, d comparison. For example, respectively, for OxF and API. The results of

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COMPARISON OF API 20E AND OXI/FERM SYSTEMS 225

this studycomparedwell with others (1, 4) with

a similar variety oforganisms. The organisms

used in thisevaluationwerevirtualconsecutive

isolates of NFB and OPFB recovered from

clin-icalmaterial and probably constitute the same

distribution oforganisms found in many

labo-ratories. Incontrastto apreviousstudy

employ-ingselected andinfrequentlyencountered orga-nisms (6),fivespecies of commonly found NFB accounted for 76% of all isolates encountered

during the studyperiod. The accuracy of iden-tification at the specieslevel of these common strainswas 97.6%(OxF)and96.7% (API).

The coding system of OxF was reduced to common and recurring codes for most orga-nisms. This was an advantage of the system.

Overall,only 63profiles werenecessaryto

iden-tify the 25 species and groups of organisms.

Fourteenof these profiles were attributed to P.

aeruginosa,although 62 strains (79%) were

iden-tified with only four codes. Asimilar situation was not seen with API. The API system pro-vided anextensivevariety of profiles which be-came adecideddisadvantageof thesystem

dur-ingidentificationattempts. That a large number

ofwell-selectedtestswillpermit more accurate

identification than will a small number is

ac-knowledged.It wasapparent, however, that the

API profile register included some theoretical

profilesbecause of the low probabilities of

oc-currence. Theinordinatelylargenumber of pro-files, many of which did not appear in the code

manuals, resulted in unnecessary and often

lengthy delays in identification because of the need for computer assistance. Indeed, a fourth of the testresults could not be found when the fornermanualwas searchedand the situation

wasimprovedlittle with the latest edition of the

manual. Eventhen,supplementaltests were

re-quired for proper identification, and difficulty

stillwasexperiencedinchoosing theappropriate

tables in theappendixforselection of ancillary tests.

Approximately

half of theorganisms

encoun-teredduring theevaluationperiodwere

fluores-cent pseudomonads. Both systems, then,

re-quired

supplemental

testsforintragroup

differ-entiationaswellasdifferentiationbetween

gen-eraandspecies.TheOxFmanual selects

cetrim-ide and growth at 42°C as the supplemental

testsof choice inmost instances. Interestingly,

ithas beenshown thatutilization of acetamide

perfectly parallels growth at 420C among the

fluorescent

pseudomonads

(5;

unpublished

data).Forthisreasonandbecauseselected

non-oxidative organisms also alkalinize acetamide,

useofacetamideis anacceptablesubstitutefor tests ofhightemperature tolerance. Hence, an

acetamideandcetrimide slant should be added

TABLE 5. Number of strainsreportedat 24and 48 hofincubation

P. A. P., A. P. Mc Fla P. CI P. P. A. cr CI P. Al A. P. No. of Organism strains tested aeruginosa 78 anitratus 65 maltophilia 28 Iwoffi 23 putida 23

)raxellasp. 16 Lvobacteria 11

cepacia 10

)CVe 7

fluorescens 7

multocida 7

xylosoxidans 5

DC IIk 6

DCVa 3

acidovorans 3

Icaligenes sp. 3

hydrophila 2

stutzeri 1

Total

No. of strains No. ofstrains byOxF at: byAPI at: 24h 48h 24h 48h

0 78 42 36

0 65 51 14

0 28 7 21

0 23 0 23

0 23 8 15

0 16 0 16

0 11 0 11

0 10 7 3

0 7 1 6

0 7 1 6

0 7 0 7

0 5 0 5

0 6 0 6

0 3 0 3

0 3 0 3

0 3 0 3

0 2 0 2

0 1 0 1

298 0 298 117 181

(39)a (61)

'Numbers inparentheses indicate percents.

to themotility stab andtriplesugar ironslantas

asupplemental battery for routine inclusionto

both of the API and OxF systems.

Both of the microsystems offer the opportu-nity for a serious attempt at identification of NFB and the OPFB. The API system seems more suited for identification of the

oxidase-negativeNFB(99.2%correct) than the

oxidase-positiveNFB(82.3% correct).On the other

hand,

the OxF systemseemssuited for both

oxidase-positive (92.6%) as well as oxidase-negative

(99.2%)

groups even thoughitwas essentialfor workerstorecognizeapossible oxidase-negative

NFB toapplytheOxFsystem.

This study was undertaken to ascertain the

suitabilityof the API 20E and OxFsystems for

identifyingclinicalisolates of NFB and OPFBas

found in the clinical

microbiology laboratory.

Testresultswere thoseobtained afterworkers

wereinstructedintheproperuseof the OxF and

APIsystems.Still,total relianceonbasic codes

mustbeavoided because

judgment

and

experi-enceis

indispensable

to

good

performance

and properidentificationof thesebacteria.Italso is

imperative

thatthesesystemsare not

placed

in thehands of

inexperienced

workers,

but in those of

experienced

workers to

simplify

their tasks.

LITERATURE Cr1ED

1.Dowda, H. 1977. Evaluation oftworapidmethods for identificationofcommonlyencounterednonfermenting

oroxidase-positive,gram-negativerods. J. Clin. Micro-biol. 6:605-609.

2. Gilardi,G.L.1973.Nonfermentativegram-negative

bac-VOL. 9,1979

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teria encountered in clinical specimens. Antonie van Leeuwenhoek J. Microbiol. Serol.39:229-242. 3. Isenberg, H. D., and J. Sampson-Scherer. 1977.

Clin-ical laboratory evaluation of a system approach to the recognition of nonfermentative or oxidase-producing gram-negative, rod-shaped bacteria. J.Clin. Microbiol. 5:336-340.

4. Nord, C. E., B. Wretland, and A. Dahlback. 1977. Evaluation of two test kits-API and OxiFerm tube-foridentification of oxidative-fermentative gram-nega-tiverods.Med.Microbiol. Immunol. 163:93-97. 5. Oberhofer, T. R., J. W. Rowen, and G. F.

Cun-ningham. 1977. Characterization and identification of

gram-negative, nonfermentative bacteria. J. Clin. Mi-crobiol. 5:208-220.

6. Oberhofer,T.R.,J. W.Rowen,G. F.Cunningham, and J. W. Higbee. 1977. Evaluation of the Oxi/Ferm tube system with selected gram-negative bacteria. J. Clin. Microbiol. 6:559-566.

7.Pickett, M. J., and M. M. Pederson. 1970. Characteri-zationofsaccharolyticnonfermentative bacteria asso-ciated with man.Can.J.Microbiol.16:351-362. 8. Weaver, R.E.,H. W.Tatum, andD.C.Holrs.1972.

The identification of unusualpathogenic gram-negative bacteria.Preliminary revision. Center for Disease Con-trol,Atlanta, Ga.

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