JOURNAL OF CLINICAL MICROBIOLOGY, Mar. 1980, p. 220-2250095-1 137/80/03-0220/06$02.00/0

Vol. 11, No. 3

Rapid Semiautomated Screening and Processing of UrineSpecimens

RONALD D. JENKINS,' DEVON C. HALE,'t AND JOHN M. MATSEN 2*Departments of Pathology' and Pediatrics,2 University of Utah College of Medicine, Salt Lake City,

Utah 84132

A rapid urine culture procedure was evaluated in which positive urines weredetected by using light-scatter photometry (Autobac). Specimens were analyzedat 3, 5, and 6 h. Specimens detected as positive at 3 h were then further evaluatedby a direct 3-h susceptibility procedure (Autobac) and by a 4-h identificationprocedure (Micro-ID). Of 949 specimens, 175 had >105 colony-forming units perml by colony count. Of these latter specimens, 75.4% had been detected by 3 h,and 95.4% were detected by 6 h. Of specimens positive by Autobac at 3 h, 96%(95.7%) had >105 colony-forming units per ml. If pure by Gram stain, thosepositive specimens were inoculated to direct susceptibility and identificationsystems. When direct Autobac susceptibilities were compared with the standardAutobac method done from the plate the following day, discrepancy rates were1.3% very major, 2.1% major, and 7.4% total. The direct identifications were 94%(94.2%) correct when using the Micro-ID manual and a collection of octal patternsunique to this system, in which urine/broth culture inoculum was employedinstead of the usual organism colony suspension. Those urine specimens negativeafter screening at 3 h were evaluated at 5 and 6 h, and an additional 126 specimenswere detected as positive. These were then processed by routine plate inoculation,due to the limitations of the work day. By 6 h, 95.4% of specimens with >105colony-forming units per ml were detected. The 4.6% false-negative results con-sisted of patients on antibiotics, or slowly growing bacteria suspected of beingdistal urethral contaminants. Thus, 83.5% of the urine cultures received by 9:00a.m. (10.6% 3-h positives and 72.9% negative at 6 h) could be evaluated andreported within one 8-h work day.

Several studies have been reported recentlydescribing screening methods for bacteriuria.Most of these screening methods generate pre-liminary reports which establish the existence ofinfection without providing organism identifica-tion or antibiotic susceptibility. Thrupp et al. (9)proposed a urine culture technique which in-cluded screening for bacteriuria with light-scat-ter nephelometry, rapid direct gram-negativebacilli identifications using Pathotec strips (Gen-eral Diagnostics, Division of Warner-LambertCo., Morris Plains, N.J.), and direct antimicro-bial susceptibility testing using light-scatter pho-tometry (Autobac-Pfizer Diagnostics, NewYork, N.Y.). We have attempted to evaluate andmodify that system to provide a practical clinicalmicrobiology laboratory method.

MATERIALS AND METHODSSpecimens. The Clinical Microbiology Laboratory

at the University of Utah Medical Center supplied 949urine specimens, of which 549 were a collection ofroutine urine culture specimens obtained over an 8-

t Present address: Infectious Disease and Clinical Micro-biology, Riverview Hospital, Idaho Falls, ID 83401.

week period. The remaining 400 specimens were col-lected from a group of catheterized patients. Speci-mens from the latter group were collected after inser-tion of an indwelling Foley catheter and then daily aspart of an ongoing catheter study. These catheterspecimens were rejected from the screening study oncethey contained a colony count of greater than 105colony-forming units (CFU) per ml, to avoid positivespecimen repetition. All specimens were refrigeratedat 4'C after initial processing by the Clinical Micro-biology Laboratory, and were saved for screening thefollowing morning. Specimens older than 24 h wererejected. A repeat plate quantitation was carried outin conjunction with the urine screening procedure.

Instrumentation. The instrument used to measurelight scatter was the Autobac, a system comprised ofa photometer module and an incubator/shaker de-signed to rotate 30 cuvettes at a specific speed (220rpm) and temperature (37°C). Light-scatter photom-etry measured turbidity by converting the light scatterby the organisms in suspension into a measurablevoltage reading. An increase in turbidity correlatedwith an increase in light scatter, resulting in a decreasein the voltage reading.

Quantitative urine culture. All urines werestreaked with a 0.001-ml calibrated loop on to sheepblood agar and MacConkey agar plates, and a colonycount was read at 18 to 24 h (2). These agar plates

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SCREENING AND PROCESSING OF URINE SPECIMENS 221

were inoculated within 1 h of the time that the Auto-bac cuvette was inoculated with the same specimen.Screening procedure. For the purposes of this

study, 105 CFU/ml was considered a significant colonycount as shown as Kass (5). The screening of urinesby Autobac was accomplished by inoculating a brothchamber with urine and observing for a change involtage at timed intervals. As described by Thrupp etal. (9), a positive urine is detected when the photom-eter voltage drops more than 0.2 V.The Autobac cuvette was filled with 18 ml of low-

thymidine Eugonic broth, resulting in each chamberreceiving approximately 1.4 ml of broth. Each urinespecimen was pipetted into two cuvette chambers inamounts of 0.1 and 0.2 ml. The cuvettes were placedin the 37°C incubator/shaker and rotated at 220 rpm.After incubating initially for 15 min to equilibrate thetemperature, and to provide a more homogeneousmixture to dissolve crystalline material, each cuvettewas then read on a photometer in the "calibrate mode"for a base-line reading. Additional readings were doneat 3, 5, and 6 h. The urines found to be positive after3 h of incubation were assessed for purity by a Gramstain and subcultured immediately to a rapid directidentification and a rapid antibiotic susceptibility sys-tem. Those urines not positive at 3 h were reanalyzedat 5 and 6 h by the photometer.Gram stain. Gram stain reagents were prepared in

accordance with Hucker's modification (6). All urinespositive by Autobac screen at 3 h were Gram stainedfor a check of purity. Predominantly pure stains weredefined as those in which an oil immersion field full ofthe predominant organism contained less than 10 or-ganisms of a different morphology.

Direct antimicrobial susceptibilities. Direct an-timicrobial susceptibility tests were performed on allcultures positive after 3 h of incubation and for whichthe Gram stain was pure or predominantly pure. A fewdrops of the turbid screening broth were removed bysterile pipette to inoculate a buffered-saline tube,which was standardized on the photometer to theproper range of turbidity. The susceptibility procedurewas performed according to the manufacturer's in-structions, using low-thymidine Eugonic broth (7, 8).A sheep blood agar plate was inoculated from thecuvette growth to assess specimen purity. A routineAutobac susceptibility test was performed the follow-ing day using organisms obtained from the puritycheck plate or the sheep blood agar quantitation plateof that specimen. The antimicrobial agents used arerecorded in Table 1.

Identification procedure. Micro-ID (General Di-agnostics) was used for the identification of gram-negative bacilli. Micro-ID is a 15-test biochemical stripmade specifically for a 4-h identification of Entero-bacteriaceae (1). The standard method for Micro-IDidentification was modified by using several drops ofthe turbid screening broth and inoculating a 4-ml tubeof saline (0.85%) to reach a McFarland no. 0.5 standard(6). Occasionally, additional time was needed to pro-vide a sufficiently turbid suspension, after photometeranalysis gave a positive reading, to gain the requiredinoculum for the Micro-ID method.A repeat Micro-ID strip was inoculated the follow-

ing day with organisms from the purity or quantitationplates by using manufacturer's recommended proce-

TABLE 1. Antibiotics used in susceptibility testing

For gram-negative rods Amt For gram-positive Amt(tg) cocci (,ug)

Trimethoprim/ Ampicillin ..... 4.5sulfamethoxazole ... 18 Ampicillin ..... 0.22

Nitrofurantoin ....... 15 Tetracycline ... 0.5Tobramycin ..... 10 Methicillin .... 5Tetracycline ......... 1.2 Kanamycin .... 22Kanamycim ....... 22 Gentamicin 9Gentamicin ...... 9 Erythromycin 2.5Colistin ........... 13 Clindamycin ... 2Chloramphenicol ..... 4 Ampicillin ... 4.5Cephalothin ......... 15 Penicillin 0.20Carbenicilin ......... 120 Cephalothin 15

dure. Organisms were identified by interpreting thetest strip reactions and converting the results to anoctal number. The identification manual used was thepreliminary edition published in March 1978. Thestandard identification used for comparison was a setof classical biochemical tests used by the clinical lab-oratory. Those included triple sugar iron agar, lysineiron agar, motility-indole-ornithine decarboxylase me-dium, Simmons citrate agar, phenylalanine deami-nase-urea broth, and, when necessary, Voges-Pros-kauer, deoxyribonuclease, acetate, and sugar fermen-tations, as recently described (1). Organisms wereidentified according to Edwards and Ewing (4).

RESULTSThe difference in the rate of false-positive and

false-negative results with urine screen inoculumsizes (0.1 or 0.2 ml) was not statistically signifi-cant. Therefore, the figures cited in the text willreflect the data using 0.1-ml inocula for the sakeof simplicity, unless otherwise stated. (Tables 2and 3 bear out this conclusion.)Of the 949 urines processed, 175 were found

to contain greater than 105 CFU/ml by cali-brated loop technique. At 3 h, the false-negativerate (false-negatives divided by the total posi-tives by the calibrated loop technique) (3) was24.6% (Table 2). Of those specimens positive byloop, 75.4% were detected by screening at thattime. After 6 h, the false-negative rate droppedto 4.6%. Of the eight urines (colony countsgreater than 105 CFU/ml) not detected by Au-tobac after 6 h, four of the patients were receiv-ing antibiotics to which the organism was sus-ceptible. If one excluded those four urines be-cause the specimen would have been plated forquantitation due to patient therapy, the false-negative rate would be 2.3%. The remaining foururines included two samples containing Staph-ylococcus epidermidis, one with diphtheroids,and one with yeast.

False-positives are shown in Table 3. At 3 h,the false-positive rate (false-positives divided bytotal negatives by loop) (3) was 1%. At 6 h, the

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222 JENKINS, HALE, AND MATSEN

TABLE 2. Inoculum differences in false-negatives byAutobac urine screening compared to the calibrated

loop method0.1-ml cuvette 0.2-ml cuvette

Time inoculum inoculumSpecimens (h)No. Ratea No. Rte

Clinical 3 29 21.0 28 20.36 3 2.2 5 3.6

Catheter 3 14 37.8 14 37.86 5 13.5 5 13.5

Total 3 43 24.6 42 24.06 8 4.6 10 5.76b 4 2.3 5 2.9

a False-negative rate = False-negatives by screening,divided by the total positives by calibrated loop tech-nique (3).bExcluding patients on antibiotics.

TABLE 3. Inoculum differences in false-positives byAutobac screening compared to calibrated loop

method0.1-ml cuvette 0.2-ml cuvette

Time inoculum inoculumSpecimen (h) tea

No. Ra No. Rat

Clinical 3 3 0.7 5 1.26 72 17.5 80 19.5

Catheter 3 3 0.8 6 1.76 24 6.7 22 6.1

Total 3 6 0.7 11 1.46 96 12.4 102 13.2

a False-positive rate = False-positives by screening,divided by total negatives by calibrated loop tech-nique.

false-positive rate increased to 12.4%. Of thefalse-positives detected, 49.0% had colony countsabove 104 CFU/ml, and 79.2% had colony countsabove 103 CFU/ml. This quantitation would beapparent in the routine laboratory work-up ofurines positive by screening at 6 h, since all ofthese samples would be streaked on sheep bloodagar and MacConkey agar plates for overnightincubation and quantitation. Four false-positiveresults were obtained due to either cuvette leak-age between chambers or spill-over during shak-ing. Only once did this occur by 3 h of incubation.Table 4 shows a breakdown as to when differ-

ent organisms became positive. Enterobacteri-aceae were more frequently detected at 3 h,whereas yeast and gram-positive cocci were sig-nificantly slower.We evaluated the screening detection of all

urines that had any growth on quantitative plate

J. CLIN. MICROBIOL.

cultures to determine the recovery rate, primar-ily at 6 h, of those urines with 104 organisms perml. At 6 h, all specimens with greater than 50,000CFU of Enterobacteriaceae per ml were de-tected from patients not receiving antimicrobialtherapy. For the Enterobacteriaceae, 77.3% (17/22) of all specimens with 10,000 to 100,000 CFU/ml, and 89.5% of those with 12,000 to 100,000CFU/ml, were detected. If one also includespotential contaminants and non-Enterobacteri-aceae isolates, only 58.8% (47/80) of the total ofall organisms present at over 10,000 but less than100,000 CFU/ml were detected. The recoveryfor specific groups of organisms, present at over10,000 but less than 100,000 CFU/ml, was asfollows: yeast, 41.7% (5/12); Staphylococcus,40% (4/10); streptococci, 66.7% (14/21), withmost being enterococcus detected in this range;diphtheroids, 55.6% (5/9); and Pseudomonas,66.7% (2/3). Three patients from whom 104 to105 CFU of Enterobacteriaceae were isolatedper ml were receiving antimicrobial agents andare not in the above statistical tabulations. Thesystem failed to detect each of these three; how-ever, they were identified because of the policyof plating all specimens from patients receivingantimicrobial agents.Purity Gram stain. Of the 138 urines posi-

tive at 3 h and stained for purity, 118 (85.6%)were found to be pure or predominantly pure.Of these, 101 were gram-negative rods, 16 weregram-positive cocci, and 1 was comprised ofdiphtheroids. The Gram stain culled 86.3% ofthe mixed cultures.Antibiotic susceptibilities. Direct anti-

biotic susceptibility tests were run on 116 urinesfound positive at 3 h. Of these 116, 95.7% (rep-resents a 1% false-positive, using the definitiongiven above) had colony counts in excess of 105CFU/ml, and all had colony counts in excess of103 CFU/ml. The following day, 126 susceptibil-ity tests were repeated for comparison. The 10additional organisms were morphological var-iants, with different antibiotic susceptibility pat-terns, found on quantitation plates in excess of

TABLE 4. Timing of the detection of urines havinggreater than 105 CFU/ml

% Positive after incuba-

Organism tion periods of:3h 6h

Enterobacteriaceae 89.6 97.9Pseudomonas sp. 70.0 90.0Gram-positive cocci 60.7 89.3Diphtheroids 33.3 83.3Yeast 0 87.5

Totals 75.4 95.4

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SCREENING AND PROCESSING OF URINE SPECIMENS 223

105 CFU/ml. The discrepancy rates for gram-negative bacilli were 1.5% very major, 2.3% ma-jor, and 4.4% minor. For purposes of definition,we have assumed that the repeat susceptibilitytest is the standard for comparison, since it wasperformed on a known pure culture. A verymajor discrepancy is a change, on repeat suscep-tibility testing, of a result from susceptible toresistant, and a major discrepancy is a changefrom resistant to susceptible. A minor discrep-ancy is any change to or from an intermediatesusceptiblity value. The reader should bear inmind that the repeat test in this instance wasthe "standard," assumed more likely to be "cor-rect." Gram-positive cocci gave 0% very major,1.6% major, and 2.6% minor discrepancy rates.Three antibiotics, chloramphenicol, cephalo-thin, and nitrofurantoin, accounted for 62.9% ofthe major and very major discrepancies forgram-negative bacilli. Gentamicin, cephalothin,and erythromycin accounted for 100% of themajor and very major discrepancies for gram-positive cocci.Of the 116 urines eligible, after Gram-stain

analysis for direct susceptibility testing, 9 weresubsequently found to contain at least two or-ganisms with colony counts greater than 105CFU/ml. The susceptibilities of the more rap-idly growing organisms were expressed. Theslower-growing organisms included: enterococci(6), Pseudomonas (1), staphylococci with a Pro-teus (1), and Proteus mirabilis (1). Since thesusceptibility patterns of gram-positive coccicannot be correlated with those ofgram-negativebacilli, the susceptibilities of the slower-growingorganisms were not incorporated into the per-centage correlation figures. Of the nine mixedcultures, five were recognized in the purity Gramstain but were set up because of a single orga-nism predominance. If one were to exclude these,3.4% of the susceptibilities reported would havebeen from specimens on which we did not rec-ognize a mixture of two or more significant or-ganisms.

Identification. A Micro-ID identificationwas performed on 101 urines found positive withgram-negative rods at 3 h. The following day,109 identifications were performed, which in-cluded the morphological variants found in ex-cess of 105 CFU/ml on the sheep blood agar orMacConkey agar plates from calibrated loopstreaking, and also included one culture whichcontained two different gram-negative rods. Ofthe direct identifications, 95.0% were done onurines with colony counts exceeding 105 CFU/ml.A problem was encountered when using the

Micro-ID kits, in that the buffering action of theEugonic broth with which the Micro-ID saline

inoculum was made caused interference in sev-eral biochemical reactions. These included thesugar fermentations, o-nitrophenyl-fl-D-galacto-pyranoside, and indole production. Thoughcharacteristic reactions resulted from this inter-ference, the octal patterns keyed out incorrectlyin the identification manual. A correct key-outwas obtained only 58.4% of the time, using theidentification manual. However, using additionaloctal patterns that were unique to this systemand which were recognized as being character-istic of certain organisms, 94.1% of the isolateswere identified correctly. (These octal patternsare: for Escherichia coli, 20037, 20417, 20437,20137, 21417, 21436, 21451, 22037, 23437, 62431,and 63471; for Klebsiella pneumoniae, 60600and 60660; for Proteus rettgeri, 32100; and forPseudomonas aeruginosa, 01700, 21700, and21100.) They include characteristic patterns forP. aeruginosa, an organism not included in theidentification manual. We have subsequentlyeliminated this problem by using centrifugedportions of the urine sample to obtain the Micro-ID inoculum.Of the 101 urines that received direct identi-

fication, 8 contained at least two organisms, eachof which had colony counts exceeding 105 CFU/ml. Four of these were detected by the purityGram stain. The gram-negative bacillus wasidentified correctly in six of the eight when usingthe identification manual, and in eight of theeight when using the new octal patterns.The Micro-ID, when done on "day 2" from

the quantitation plates, gave the correct identi-fication 95.4% of the time as compared to theconventional identification method.

DISCUSSIONBased on the screening results, a 3- and 6-h

reading on the Autobac can be used as thescreening portion of a laboratory urine process-ing method, provided that the urine specimensarrive in the laboratory in a timely fashion. The3-h reading provides a low false-positive rate,and those 3-h positive urines have a high prob-ability of containing a single organism in signif-icant numbers. By including a 6-h reading, thereis assurance that 95% of the positive urines aredetected. Those not detected are more likely tocontain organisms frequently viewed as ques-tionable pathogens, or to come from patientsreceiving antibiotics, who would, under our pro-posed protocol, have urines streaked to primaryisolation (sheep blood or MacConkey agar)plates. Urines negative at 6 h can be reported asnegative with a high degree of reliability. Arecommended procedure would be to performrapid direct identifications and antibiotic suscep-tibility tests on 3-h positives. Urines positive at

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224 JENKINS, HALE, AND MATSEN

6 h would be plated out routinely from theoriginal refrigerated urine and worked up withrapid identifications and susceptibilities, if war-ranted, the following day. In situations wherethere is a low incidence of positives, such as inscreening large asymptomatic populations, itmight be practical to use only a 6-h Autobacreading.This screening method is designed to detect

urines containing high colony counts. In thatlight, urines from patients in which lower colonycounts may be significant should be processedroutinely, in addition to this rapid method.These patients include those on antibiotics,those with urinary catheters, and those fromwhom suprapubic aspirates were used for speci-men collection. The primary reason to process

routinely urines from patients on antibiotics isthat the antibiotics may prevent growth in thescreening broth, yet allow growth when dis-persed on the surface of solid media. A total of50.0% of the false-negatives at 6 h in screeningby Autobac occurred in patients receiving anti-biotics, including both of the false-negativePseudomonas isolate specimens.Many physicians and microbiologists might

have concern for a system in which specimenswith numbers approaching 105 might be missed.The screening procedure picked up at 6 h allEnterobacteriaceae over 50,000 CFU/ml and89.5% of the Enterobacteriaceae over 12,000CFU/ml, with a similar recovery for enterococ-cus. Two of three Pseudomonas isolates in the104 to 105 range were detected. Recovery figureswere not as high for non-enterococcal strepto-cocci, staphylococci, and yeasts.The false-negative rate will drop to less than

3% if all urine specimens from patients receivingantimicrobial agents and which are negative byurine screen are plated out after the 6-h reading.The organisms that then remain in the false-negative category are almost all perineal con-

taminants. Significant pathogens missed by thismethod were less than 1%.To minimize the problem of false-negatives

due to the presence of antimicrobial agents, theUniversity of Utah Clinical Microbiology Labo-ratory sends out reminders to physicians whoprovide inadequately filled out forms. This hasimproved the amount and quality of informationon the slips, so that 85% of slips received are

now properly completed.Of the positive urines evaluated for purity by

Gram stain, 90 contained a single organism. Themajority of mixed cultures, in which both orga-nisms were observed in significant quantities,contained gram-negative bacilli with entero-cocci. It was evident that enterococci in signifi-cant numbers may be outgrown in the screening

procedure prior to the purity Gram stain. In thatlight, it is recommended that all urines foundmixed by Gram stain be processed routinely onquantitation plates to detect the presence ofadditional organisms with significant colonycounts.The high correlation of direct antibiotic sus-

ceptibilities with those suceptibilities done rou-tinely gives confidence that this method can beused in a routine laboratory setting.The accuracy of the Micro-ID in direct iden-

tification of gram-negative bacilli was hamperedby the buffering action of the Eugonic broth.Interpreting Micro-ID reactions was difficult atbest because the degree of variance from octalpatterns listed for appropriate organism identi-fication was dependent on the amount of brothinoculum needed to bring the saline to theMcFarland no. 0.5 turbidity. With a turbidscreening chamber, only a few drops of brothwere necessary for inoculation, and the reactionshad no interference. With several urines, whenthe screening chamber was minimally turbid, 1ml or more was needed to bring the saline to theMcFarland no. 0.5 standard turbidity. It wasdetermined that 0.2 ml of Eugonic broth used inthe saline inoculum allowed normal reactions,whereas 0.5 ml of broth used in the saline inoc-ulum was enough to cause abnormal reactionsby 4 h.To correct this problem, we have subse-

quently explored several alternatives. (i) Theorganisms can be spun down in the screeningbroth, and the supernatant broth is then aspi-rated and replaced with saline. (ii) The labora-torian can delay setting up the Micro-ID untilthe broth reaches a turbidity wherein a smallerinoculum can be used. (iii) Any specimen withan octal number not keyed to an anticipatedurinary pathogen can be allowed to incubatelonger. It was found that by 16 h, all of thesenon-organism-related patterns had reverted tonormal, except those in which at least 2 ml ofEugonic broth was used in the saline inoculum.(iv) The last alternative would be to use anidentification method in which the buffering ac-tivity of the broth was considered in creating theoctal code listing, and, therefore, would not af-fect the identification. Any one of those alter-natives could offer high-accuracy identifications.With the urine processing system, 10.6% of the

urines (57.7% of all significant positives) receiveda same-day identification and antimicrobial sus-ceptibility test. An additional 72.9% of the urineswere negative by screen after 6 h. Thus, 85.5%of the workload was completed within approxi-mately 8 h. This figure dropped to 82.3% whenwe used the recommended method of workingup only urines with pure Gram stains. In that

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SCREENING AND PROCESSING OF URINE SPECIMENS 225

context, the urine processing method offers aconsiderable time and effort savings for the clin-ical microbiology laboratory and a marked de-crease in the amount of time between specimencollection and final laboratory result reporting.

ACKNOWLEDGMENTS

This study was supported in part by a grant from PfizerDiagnostics Division, Pfizer, Inc., Groton, Conn. Micro-ID kitswere graciously provided by Zoltan Komjathy of GeneralDiagnostics Division, Warner-Lambert, Co., Morris Plains,N.J.

The assistance and cooperation of the staff of the ClinicalMicrobiology Laboratories, University of Utah Medical Cen-ter, and the excellent secretarial help of Glenna A. Bytendorpand Connie Staples are gratefully acknowledged.

LITERATURE CITED1. Aldridge, K. E., B. B. Garder, 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. Barry, A. L., P. B. Smith, and M. Turck. 1975. Cumi-tech 2, Laboratory diagnosis of urinary tract infections.Coordinating ed., T. L. Gavan. American Society forMicrobiology, Washington, D.C.

3. Colton, T. 1974. Statistics in medicine, p. 90-96. Little,Brown and Co., Boston.

4. Edwards, P. R., and W. H. Ewing (ed.). 1972. Identifi-cation of Enterbacteriaceae, 3rd ed., p. 21-42. BurgessPublishing Co., Minneapolis.

5. Kass, E. H. 1957. Bacteriuria and the diagnosis of infec-tions of the urinary tract. Arch. Intern. Med. 100:709-714.

6. Paik, G., and M. T. Suggs. 1974. Reagents, stains, andmiscellaneous test procedures, p. 930-950. In E. H.Lennette, E. H. Spaulding, and J. P. Truant (ed.),Manual of clinical microbiology, 2nd ed. American So-ciety for Microbiology, Washington, D.C.

7. Praglin, J., A. C. Curtis, D. K. Longhenry, and J. E.McKie, Jr. 1974. Autobac 1-a 3-hour automated an-timicrobial susceptibility system. H. System descrip-tion, p. 199-208. In C. Heden and T. Illeni (ed.), Auto-mation in microbiology and immunology. John Wileyand Sons, Inc., Publisher, New York.

8. Thornsberry, C., T. L. Gavan, J. C. Sherris, A. Bal-ows, J. M. Matsen, L. D. Sabath, F. Schoenknecht,L. D. Thrupp, and J. A. Washington I. 1975. Lab-oratory evaluation of a rapid, automated susceptibilitytesting system: report of a collaborative study. Antimi-crob. Agents Chemother. 7:466-480.

9. Thrupp, L. D., P. D. Heinze, and M. A. Pezzlo. 1976.Direct rapid urine cultures: same day reporting of quan-titation, speciation and antimicrobial susceptibilitytests, p. 17-22. In A. Balows (ed.), ASM Symposium ofAutomation in Clinical Microbiology. Pfizer Diagnos-tics, New York.

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