Urine culture

URINE CULTURE Office Technique STUART SHIKORA, M.D. PAUL GONICK, M.D. R I C H A R D G U T E K U N S T , PH.D. From the H a h n e m a n n Medical College and Hospital, Philadelphia, Pennsylvania

ABSTBACT-A controlled study is presented which confirms the reliability of a dip-paddle office culture system for the detection of bacteriuria within twenty-four hours.

Prevalence of urinary tract infection makes it one of the most common diagnoses made by clinicians. As a complication of instrumentation, surgery, and antimicrobial chemotherapy, infection is especially common. 13 Diagnosis cannot rest solely on the signs and symptoms classically associated with infection of the upper and lower urinary tracts because atypical clinical pictures frequently occur. In some cases, persistent bacteriuria of significant proportions may be the first indication of previously unsuspected and potentially serious urinary tract disease in an asymptomatie patient2 Diagnosis is facilitated (and antimierobial chemotherapy more accurately determined) by culturing urine obtained either from patients suspected of having an infection or from those undergoing a screening program. Use of urine culture in the diagnosis of urinary tract infection is no simple matter, for correct interpretation of culture results presumes the results' accuracy. Methods of collection, handling, and culturing of urine are common sources of error in the final culture report, interfering with correct interpretation. F r e q u e n c y of false reports of the presence of infection reflects the departure from procedures l~nown to minimize t h e s e sources of error. Changes of procedure which further reduce the potential for error

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would enhance the accuracy of culture reports and, therefore, the interpretation based on them. One such change, immediate culturing , is described in this report. Criteria established for diagnosis of urinary tract infection based on urine culture d e p e n d on the methods used to collect, handle, and culture the urine. All culture methods used b y clinical laboratories are tested for accuracy of estimation of concentration and specie distribution of organisms present in urine specimens. Whether or not results of these cultures represent the content of the specimens w h e n they are obtained, depends on how the specimens were handled. Unless culturing is performed immediately after collection, the specimen requires refrigeration at 4°C. to preserve microbial viability and inhibit multiplieation2 Such preservation maintains accurate organism con; centration and specie distribution without affecting viability for up to ten days. 4 However, refrigeration is not always available in clinical areas and is rarely available for transportation to laboratory facilities. E v e n w h e n availablel refrigeration often is delayed inadvertently for several hours, a sufficient Iength of time for small numbers of contaminant organisms t~ multiply into the range of suspect or slgmfica~ bacteriuria. 3,5

UROLOGY

/ JANUAI~Y 1974

/ V O L U M E III, NUMBER ~

Method of collection affects validity of urine culture results by introducing the potential for specimen contamination. While pereutaneous needle aspiration of bladder urine carries the least: potential for specimen contamination, patient discomfort and morbid state militate against the routine use of this procedure2 "~ Catheterization of the urinary bladder carries a potential for specimen contamination, with a 9, to 4 p e r cent risk of iatrogenic bladder infeetion.Z,6,s Nevertheless, it is preferred in cases in wllich a midstream-voided specimen has a high probability of heavy contamination, 1° or antimicrobial chemotherapy, heavy diuresis, or bacteriostatic bladder conditions might produce cillture reports of bacteriuria indistinguishable from levels of contamination21 The midstreamVoided method of urine collection is most popular because it combines aeeuraey with safety, privacy, and fewer demands on professional time.l. 9,12

or equal to i0 a, 104, 105, or equal to or greater than 106, and as gram-positive or gram-negative, or mixed culture, by visual comparison to photographs of growth on paddles dipped in broths of calibrated organism eoncentration. The specimen was stored in a refrigerator for no more than four hours until cultured by standardized laboratory technique. This technique features calibrated loop inoculum, serial dilution, and glass rod surface-spread on blood agar and eosin methylene blue plates. The laboratory involved was the hospital facility for diagnostic microbiology. Readings by a microbiologist from this laboratory were compiled independently without eommunieating with the evaluating physician until all readings were completed. These served as standards of reference for eomparison. One hundred ninety-eight specimens were eolleeted from 193 consecutive patients seen at a urologist's private office. Results

Method In evaluating the interpretation of bacterial growth on a commercially available diagnostic c6!turing test for baeteriuria,* we tested accuracy of t h e product and studied effect of shortening time between specimen collection and culture; also of interest was the frequency of sterile and minimally contaminated cultures from midstream-voided specimens. The office culture system in this eontrolled study was a dip-paddle technique similar to a dip-slide system reported elsewhere. ~3 Both are refinements of a dip-slide technique devised by Maekey and Sandys in 1965,14 shown to be reliable by Cohen and Kass 1~ after improvements hy Guttman and Naylor26 Culture media on the paddles were eosin methylene blue on one side to grow gram-negative organisms, and tryptiease soy agar with 2,3,5-triphenyltetrazolium on the o t h e r side to grow gram-negative or grampositive organisms. All urine speeimens were sampled immediately after collection by immersing the lower half of the paddle in the specimen, then replacing the paddle in its holder tube which permitted built-in tines to streak the urine onto the upper half of the media. After twenty-four hours of incubation at 37°C. in a desk-top incubator, the paddle growth was independently rated by a physician as less than

*Clinicult Culture Test for Bacteriuria b y Smith Ktine Diagnosties.

UROLOGy / JANUARY 1974 / VOLUME III, NUMBER 1

Of the I98 urine specimens collected, 19i were obtained by midstream-voiding and 7 by catheterization. Five of the eatheter specimens were matched by midstream specimens taken from the same patients at the same time. Seventy-one specimens showed no growth by both culture methods, 51 obtained from men, 20 from women; 67 of the 71 were obtained by the midstream method. Twenty-eight specimens showed growth of 105 organisms per milliliter or more by both methods of culture. Seventy specimens showed growth between 102 and 104 organisms per milliliter by both methods of culture. Of the remaining 29 specimens, 25 showed no growth by one method of eulture and some growth by the other. Four showed disparities in colonial estimate, being 105 by the laboratory method and 104 by the office paddle method. Of the 5 catheter-midstream pairs, both collection methods produced the same eulture results for each of 4 pairs. The fifth pair showed no growth by both culture methods for the catheter specimen but unequal colonial estimates by the culture methods for the midstream speeimen (Tables I and II). Of the 25 specimens showing growth by one culture method but not the other, 17 showed no paddle growth and 8 no laboratory growth. The 8 paddles corresponding to laboratory reports of no growth contained only a few colonies of coagulase-negative Staphylococcus, which could have been introduced by breaks in aseptic handling technique of the paddles. Among the 17, there

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~[. Comparison of collection methods using paddle and laboratory colony counts

TABLE

Organisms Per Milliliter I 102 to 104* l0 Sor Greater

,

Method

Sterile

Midstream-voided Men Women Catheter Men Women TOTAL

49 18

41 57

l0 i6

9. 2 71 (36 per cent)

0 99 (50 per cent)

1

2 0 28 (14 per cent)

* O n e or b o t h culture m e t h o d s s h o w e d g r o w t h 10 2 to 10 4.

were 14 standard laboratory cultures of colony counts b e t w e e n 102 and 103, and 3 b e t w e e n 103 and 104; 14 of the 17 grew either Streptococcus or coagulase-negative Staphylococcus, and 3 grew gram-negative rods. Comment Kass 1 suggested that collection of sterile urine by the midstream technique was uncommon. In our study, 36 per cent s h o w e d no growth, while 64 per cent s h o w e d some growth that had to b e quantitated for evaluation. Five catheter-midstream pairs is too small a n u m b e r to ascribe statistical significance, although it is interesting that 4 of 5 pairs s h o w e d agreement of colony count and specie distribution. Using Kass' criterion for significant bacteriuria, that is, a colony count greater than 105 organisms per milliliter of midstream-voided urine, we found significant bacteriuria b y both culture methods on 27 midstream specimens, an ostensible infection rate of 14 per cent. Unlike the findings of Duckman et al., ~° we found that the confirmed contamination rate (colonial estimates of 102 to 104 b y both methods of culture) was only 35 per cent despite the lack of professional assistance in midstream-specimen collection. Investigators have shown the ability of specimens initially considered "sterile" to show

growth of bacteria after several hours of standing, despite strict aseptic culture and handling techniques, reflecting the ability of small numbers of bacteria to multiply in standing urine2 Possibly these 17 specimens w o u l d have shown no growth by the standard laboratory technique if culture had b e e n performed immediately after specimen collection, as was done with the paddle. Considering the possibility of contaminant growth, it is difficult to state whether the 3 specimens which showed paddle growth of 104 and laboratory growth of 105 were examples of paddle accuracy (and bacterial multiplication during storage and handling) or instances in which the paddle underestimated a significant bacteriuria. The organisms grown from each specimen were: 1 group D Streptococcus, 1 Escheriehia coli, and i Pseudomonas aeruginosa plus Herellea. The 1 paddle showing growth of 105 not confirmed by laboratory culture grew coagulase-negative Staphylococcus. This specimen and the one growing the Streptococcus were most probably instances of contamination, leaving 2 specimens in which the office procedure may have underestimated a significant bacteriuria. There were no instances of the paddle indicating a significant bacteriuria which was not v e r i f e d b y laboratory culture. Summary

TABLE II.

Comparison of culture methods

~to

Organisms I 104 105 and greater

Method

Sterile

Office paddle Standard laboratory

88 (45)*

81 (41)

29 (14)

78 (40)

89 (45)

31 (15)

* F i g u r e s in p a r e n t h e s e s indicate p e r cent.

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This controlled study confirmed the reliability of a dip-paddle office culture system for the de: tection of bacteriuria within twenty-four hours. From i91 midstream and 7 catheter specimens, the paddle technique detected 28 cases of significant bacteriuria and 168 eases of either sterile urine or specimen contamination. Only 2 eases of significant bacteriuria may have b e e n under"

UROLOGY / JANUARY 1974 / VOLUME III, NUMBER I

estimated, and no indication of significant bacteriuria was made in which such did not exist. Validity of the midstream technique for collection of urine specimens was shown. 230 North Broad Street Philadelphia, Pennsylvania 19102 (DR. GONICK) References L KASS, E. H.: The role of asymptomatie baeteriuria in the pathogenesis of pyelonephritis, in Quinn, E. L., and Kass, E. H., Eds.: Biology of Pyelonephritis, Boston, Little, Brown and Company, 1960, p. 319. ~:KAITZ, A. L., and WILLIAMS, E. J.: Bacteriuria and urinary tract infections in hospitalized patients, N. Engl. Med. 262" 425 (1960). 31::;KAss, E. H.: Asymptomatic infections of the urinary trac t, Trans. Assoc. Am. Physicians 69:56 (i956). 41:Mou T. W., and FELDMAN, H.A.: Enumeration and preservation of bacteria in the urine, Am. J. Clin. Pathol.

....i:! 35.573 (196 i). ~, BAKER, J. J., and THOMPSON, I.M.: The evaluation of i ! q n a n t i t a t i v e bacterial cultures of urine: growth rate of : : contaminants, J. Urol. 10h 761 (1969). 6:i: MONZON, O. T., et al.: A comparison of baeterial counts ....::of the urine obtained by needle aspiration of the bladder, :catheterization and midstream voided methods, N. Engl. j . Med. 259:764 (1958).

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7. SACCHAROW, L., and PRYLES, C.V.: Further experience with the use of percutaneous suprapubic aspiration of the urinary bladder; bacteriologic studies in 654 infants and children, Pediatrics, 43:1018 (1969). 8. BEESON, P. B.: The case against the catheter, Am. J. Med. 2 4 : 1 (1958). 9. KASS, E . H . : Bacteriuria and the diagnosis of infections of the urinary, tract, Arch. Intern. Med. 100:709 (1957). 10. DUCKMAN, S., CHEW, Y. W., SPITALEm, J., and STEERS, E.: Comparison of paired midstream voided and catheterization urine samples from the postpartum clinic population, Am. J. Obstet. Gynecol. 106:1184 (1970). ii. KUNIN, C. M., PETERSDORF, R. G., KIMMERSTIEL, ]ft., and RELMAN, A. 8.: Asymptomatie bacteriuria: significance and management, in Ingelfinger, F. J., Relman, A. 8., and Finland, M., Eds.: Controversy in Internal Medicine, Philadelphia, W. B. Saunders Company, 1966, p. 289. 12. RILEY, n . D.~ JR.: Diagnosis of urinary tract infection, J. Lab. Clin. Med. 52:840 (1958). 13. ARNEIL, G.C.: Detection of baeteriuria at room temperature, Lancet 1:119 (1970). 14. MACKEY, J. P., and SANDYS, C. H.: Laboratory diagnosis of infection of the urinary tract in general practice by means of dip-inoculum transport medium, Br. Med. J. 2 : 1 2 8 6 (1965). 15. COHEN, S. N., and KASS, E. H.: A simple method of quantitative urine culture, N. Engl. J. Med. 277:176 (1967). 16. GUTTMAN, D., and NAYLOR, G. Pt. E.: Dip-slide: an aid to quantitative urine eulture in general practice, Br. Med. J. 3:343 (1967).

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