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Use of the Becton-Dickinson urine culture tube with the Abbott MS-2 urine screening system
193
DIAGN MICROBIOL INFECT DIS 1984;2:193-198
Use of the Becton-Dickinson Urine Culture Tube with the Abbott MS-2 Urine Screening System Paul M. Southern, Jr., and Bobbye Luttrell
Urine specimens were obtained from 312 obstetric outpatients by sterile midstream technique and aliquots placed in both Becton-Dickinson urine culture tubes and sterile conventional tubes. Quantitative cultures were made from each tube, and each tube was screened for bacteria with the Abbott MS-2 urine screening system, The time required to detect bacteriuria was recorded for both specimens. Isolates from specimens containing >50,O00/ml gram-positive cocci or >-lO0,O00/ml gram-negative bacilli were identified and antimicrobial susceptibility tests performed. Delayed ~24 hr) quantitative cultures were done from Becton-Dickinson tubes. By these criteria, 124 urine specimens were positive in both conventional and Becton-Dickinson tubes, gscherichia coil (n = 72), Kiebsiella pneumoniae (n = 20), gnterobacter cloacae (n_ = 8), Proteus mirebilis (n = 4), group B streptococcus (_n = 12), and enterococcus (n = 8) were isolated. Time for detection of positive urine samples was similar in both types of tubes. Delayed cultures had significant numbers of false-positive results. Antimicrobial susceptibility results did not appear to be influenced great/y by Becton-Dickinson tube transport. The MS-2 cannot adequately discriminate cultures containing <50,000 colony-forming units/ml of urine. The Becton-Dickinson tube appears to be compatible for use with the MS-2for purposes of screening for bacteriuria. INTRODUCTION The Becton-Dickinson Urine Culture Kit tube was introduced in an attempt to circumvent logistic problems that frequently make prompt culture or refrigeration of urine specimens difficult to accomplish. It makes use of preservatives (boric acid-glycerol-sodium formate) to suppress bacterial growth in urine without refrigeration for up to 24 hr so that quantitative cultures may be inoculated at a convenient time, yet produce reliable results. Previous studies of the Becton-Dickinson tube have reported variable degrees of reliability of quantitative cultures, with detection rates ranging from 71 to 93% (Guenther and Washington, 1981; Hubbard et al., 1983; Lauer et al., 1979). The Abbott MS-2 apparatus is an automated system that allows screening of urine specimens for significant bacteriuria. It enables the detection of positive cultures within hours, thus permitting negative reports to be issued on the day of collection of specimens. Reports by various investigators have found the MS2 to be 94.3-99.5% accurate in detecting urine specimens containing ->105 organisms/ ml (Godowski and Hodges, 1981; Hoban et al., 1983; McCarthy, 1982; McCarthy et al., 1982; Pezzlo et al., 1982; Szilagyi et al., 1983). Godowski and Hodges (1981) used
From the Department of Pathology, The University of Texas Health Science Center at Dallas, and Clinical Microbiology Laboratory, Parkland Memorial Hospital, Dallas, Texas. Address reprint requests to: Paul M. Southern, Jr., M.D., Department of Pathology, The University of Texas Health Science Center, 5323 Harry Hines Boulevard, Dallas, TX 75235. Received August 31, 1983; revised and accepted December 23, 1983. © 1984 Elsevier Science Publishing Co., Inc. 52 Vanderbilt Avenue, New York, NY 10017
0732-8893/84/$03.00
194
P.M. Southern, Jr., and B. Luttrell
Becton-Dickinson tubes to collect urine specimens subsequently screened by the MS-2, but did not assess whether the preservatives had any effect on the outcome. Only the report of Hubbard et al., (1983) mentioned such an effect. They found a delaying effect on growth of some organisms from Becton-Dickinson tubes. The purpose of the present study was to evaluate the efficacy of collecting urine specimens in Becton-Dickinson tubes and subsequently screening them for bacteriuria with the MS-2.
MATERIALS AND METHODS Urine specimens were obtained from patients attending an obstetrical outpatient clinic for prenatal care. Many patients had symptoms referable to the urinary tract, but others were asymptomatic. Collection of specimens was supervised by a nurse. After preparation of the periurethral area, the patients voided urine that was collected in midstream fashion in a sterile container. Immediately a sample of urine was drawn into a Becton-Dickinson Urine Culture Kit tube and another into a sterile screwcapped tube, routinely used in our hospital for transporting urine to the laboratory for culture. Both tubes were sent to the Clinical Microbiology Laboratory as soon as possible. If transport could not be accomplished within 20 min, the sterile conventional tube was refrigerated. In the laboratory both tubes were streaked with a calibrated quantitative loop onto eosin-methylene blue agar, Columbia CNA blood agar, and blood agar. The quantitative loops were regularly subjected to a quality control procedure and discarded from service if they varied more than 5% from established guidelines. Each tube was also inoculated into an Ampvette of the Abbott MS-2 apparatus for purposes of screening for bacteriuria. The time necessary for the MS2 to judge a urine sample positive was recorded for both specimens. All specimens not determined to be positive by the MS-2 within 6 hr were reported as negative. The numbers and types of organisms isolated on each plate for each specimen were recorded. If the colony count exceeded 50,000/ml for gram-positive cocci or 100,000/ ml for gram-negative bacilli (unmixed cultures), all isolates were identified and antimicrobial susceptibility testing was done (on isolates from both the Becton-Dickinson tubes and conventional tubes). Testing was done by an agar dilution method using a Steers replicator (WaShington and Sutter, 1980) and also with the Abbott MS-2 apparatus (separate testing for organisms isolated from Becton-Dickinson tubes and conventional tubes). The Becton-Dickinson tubes were held an additional 24 hr at room temperature, and a delayed quantitative culture was done for comparison with the original.
RESULTS
Of the 312 urine specimens included in the study, 124 were classified as positive on the basis of colony counts. The organisms recovered and the time required for their assessment as positive by the MS-2 apparatus are shown in Table 1. The median time required for urine specimens to be judged positive was similar for conventional and for Becton-Dickinson collection tubes (overall median time, 95 and 105 min, respectively). No specimens were determined to be positive from conventional tubes and negative from Becton-Dickinson tubes, or vice versa. Specimens deemed negative by the MS-2 were analyzed closely for colony counts and organism types (Table 2). Most represented mixed cultures, or gram-postive cocci in numbers fewer than 25,000/ml. Results of specimens from conventional tubes did not differ significantly from those from Becton-Dickinson tubes. The quantitative
Use of Urine Culture Tube with Urine Screen
195
TABLE 1. Organisms Recovered and Time Required for Detection by Abbott MS-2 Urine Screening System Time (min) Organism (no.)
Type of tube
F.scherichia coli (72)
Mean Median Maximum
Conventional Becton-Dickinson Conventional Becton-Dickinson Conventional Becton-Dickinson Conventional Becton-Dickinson Conventional Becton-Dickinson Conventional Becton-Dickinson
Klebsiella pneumoniae (20) Enterobacter cloacae (8) Proteus mirabilis (4} Group B streptococcus {12] Enterococcus (8)
110 115 109 110 127.5 125 50 60 188 177 162.5 158
70 85 120 115 120 120 50 60 170 160 165 160
280 280 140 140 150 160 60 60 260 260 170 175
cultures from 24-hr delayed streaks from Becton-Dickinson tubes were significantly different in that 40 of 188 specimens had colony counts in excess of 50,000/ml (Table 2). Of these specimens, 19 contained "significant" numbers of bacteria, as defined previously, and would have been reported as positive cultures had that been the only quantitation made. The time required for urine cultures to be judged negative is shown in Table 3. Those specimens containing fewer than 10,000 organisms/ml were occasionally determined to have subthreshold growth sooner in cultures from conventional tubes, whereas this determination was made in those cultures containing more than 10,000 organisms/ml earlier in Becton-Dickinson tubes. Although this information was noted and recorded, no urine specimens with less than threshold growth were removed from the MS-2 in less than 6 hr. Of "negative" specimens with colony counts below 50,000/ml, similar proportions from Becton-Dickinson tubes (116 of 132) and conventional tubes (106 of 120) contained gram-positive cocci. Of "negative" specimens with colony counts greater than 50,000/ml, those from Becton-Dickinson tubes contained two isolates of mixed grampositive cocci, four of mixed gram-negative bacilli, and two of Lactobocillus species; those from conventional tubes contained four isolates of mixed gram-positive cocci, four of mixed gram-negative bacilli, two of Lactobacillus species and two of yeasts.
TABLE 2. Numbers of Specimens with Colony Counts Below Laboratory Standards for Positive Cultures as Determined by the MS-2 by Method of Collection and Enumeration Colony counts of specimens/ml Type of specimen
0-1000
1000-10,000
10,000-50,000
~50,000
Total
Conventional tube Becton-Dickinson tube Delayed streak
54 50 32
82 90 58
38 40 58
14 8 40 a
188 188 188
°Gram-positive cocci or mixed (group B streptococcus, 2), 28; gram-negative bacilli or mixed, 6; grampositive bacilli, 4; yeast, 2.
196
P.M. Southern, Jr., and B. Luttrell
TABLE 3. Time [min) Required for the Abbott MS-2 System to Process IScreen) Urine Specimens by Colony Count a Colony counts of specimens/ml Type of specimen
0-10,000
10,000-50,000
>50,000
Conventional tube Becton-Dickinson tube
259 299
334 238
191 113
aSomeurine specimenswere noted to have subthreshold growth in less than 6 hr, but were not removed from the MS-2 unless deemed positivebefore that time.
Specimens yielding yeasts in conventional tubes also had them isolated from Becton-Dickinson tubes, albeit in smaller numbers. Results of antimicrobial susceptibility testing did not appear to be influenced significantly by transport in the Becton-Dickinson tubes.
DISCUSSION The proportion of urine specimens in this study containing ->10 s organisms/ml (124 of 312, or 39.7%) was relatively high, but is not surprising in view of the patient population surveyed (mostly indigent obstetric patients). Likewise, the population of bacteria recovered was relatively standard for this patient group. Unlike the findings of Hubbard et al., (1983), no significant effect was observed upon the time required for the MS-2 to detect ---105 bacteria/ml of urine in specimens from Becton-Dickinson tubes compared with conventional tubes. This finding may be due in part to the inclusion in their study of several specimens containing Pseudomonas aeruginosa and Staphylococcus epidermidis, organisms for which detection was delayed or absent in Becton-Dickinson tubes. Our patients did not have infections with these species. In specimens that the MS-2 determined to be positive, we saw no discrepancy in quantitative cultures from either conventional or Becton-Dickinson tubes. All 124 specimens positive by the MS-2 had colony counts exceeding 100,000/ml in both tubes. Some specimens had higher counts from the conventional tubes; however, as all counts from the Becton-Dickinson tubes were also above 100,000/ml, no misinterpretation was possible (data not shown). This observation is in modest contrast to the studies of Godowski and Hedges (1981), Hoban et al. (1983), McCarthy (1982), McCarthy et al. (1982), Pezzlo et al. (1982), Szilagyi et al. (1983), who reported a failure rate of 0.5-5.8% in the detection of urine specimens with 10 ~ organisms/ml by the MS-2. Again, this finding may have been due to the patient population in the present study (Kass, 1978; Whalley, 1967). The data with respect to negative specimens are relatively straightforward. No misinterpretations would have resulted from reliance on the original MS-2 readings of urine samples from the Becton-Dickinson tubes. One potentially significant finding with respect to the negative cultures was the discrepant colony counts from the 24-hr delayed cultures from the Becton-Dickinson tubes: 69% had colony counts greater than those from the earlier enumeration. Of such specimens, 19 had colony counts that would have been interpreted as representing significant bacteriuria, had that been the only culture performed. This finding is in contrast to the data of Guenther and Washington (1981), Hubbard et al. (1983), and Lauer et al. (1979), who found lower colony counts after delayed cultures from Becton-Dickinson tubes. Perhaps this result was partly attributable to a change in
Use of Urine Culture Tube with Urine Screen
197
the formulation of the preservatives in the Becton-Dickinson tube (J. J. Mehl, Becton-Dickinson & Co., personal communication). It remains a potentially troublesome problem, however, and should be investigated further. We found no strikingly adverse effects of urine transport in Becton-Dickinson tubes upon subsequent antimicrobial susceptibility testing of significant bacterial isolates. Recently, Stamm et al. (1982) reported data in evaluation of young women with acute lower urinary tract symptoms. Their assessment was that the best diagnostic criterion in this population was a urinary colony count of - 1 0 z coliforms/ml in midstream urine. These findings will necessitate a reevaluation of diagnostic methods used in this population of patients. The methods used in the present study (particularly urine screening with the MS-2) were not sufficiently sensitive to detect bacteriuria at that concentration. Based upon our findings, however, quantitative cultures from the Becton-Dickinson tubes could be used in such evaluations. This concept would require more clinical information to be transmitted to the diagnostic microbiology laboratory, as well as a two-tiered set of standards regarding the constituents of significant bacteriuria. Further study will be required in this area, particularly with respect to refining rapid or automated methods of testing for bacteriuria. Our data suggest that the use of Becton-Dickinson tubes for transport of urine is compatible with subsequent screening for bacterinria with the MS-2. No significant adverse effect was encountered with antimicrobial susceptibility testing. The delayed quantitative culture (after 24 hr) from Becton-Dickinson tubes can be potentially misleading Ithat is, false-positive counts). It is not possible at present to detect bacterial colony counts of approximately 102 organisms/m] with the MS-2; therefore, it is not currently suitable for screening young women in whom acute urethral syndrome is suspected. We wish to thank Barbara McElwee, R.N., and Ms. Alice Gossett for their invaluable assistance in collecting urine specimens and Pattie Pipes for secretarial assistance. Parts of this study were supported by a grant from Becton-Dickinson & Co.
REFERENCES Godowskl KC, Hodges WJ (1981) Accuracy and effect upon clinical workload of the MS-2 urine screen and antibiotic susceptibility system. Lab Med 12:758. Guenther KL, Washington JAII (1981) Evaluation of the B-D urine culture kit. J. C/in Microbiol 14:628. Hoban DJ, Koss JC, Gratton CA, Ronald AR (1983) Urine screening with the MS-2. J Clin Microbiol 17:1061. Hubbard WA, Shalis PJ, McClatchey KD (1983) Comparison of the B-D urine culture kit with a standard culture method and with the MS-2. ] Clin Microbiol 17:327. Kass EH (1978) Horatio at the orifice: Significance of bacteriuria. I Infect Dis 138:546. Lauer BA, Relier LB, Mirrett S (1979) Evaluation of preservative fluid for urine collection for culture. I Clin Microbiol 10:42. McCarthy LR (1982) Evaluation of the MS-2 system for the detection of bacteriur/a. In Rapid Methods and Automation in Microbiology. Ed., RC Tilton. Washington, DC: American Society for Microbiology, pp 316-320. McCarthy LR, Gavan TL, Robson J, Corlett C (1982) Evaluation of the MS-2 urine screening method for detection of bacteriuria. ! Clin Microbiol 16:250. Pezzlo MT, Tan GL, Peterson EM, de la Maza LM (1982) Screen/rig of urine cultures by three automated systems. J Clin Microbiol 15:468. Stature WE, Counts GW, Running KR, Fihn S, Turck M, Holmes KK (1982) Diagnosis of coliform infection in acutely dysuric women. N Eng/I Med 307:463.
198
P.M. Southern, Jr., and B. Luttrell
Szilagyi G, Ailing V, Karmen A (1983) Comparative study of two methods for rapid detection of clinically significant bacteriuria. J Clin Lab Automat 3:117. Washington JAII, Sutter VL (1980) Dilution susceptibility test: Agar and macro-broth dilution procedures. In Manual of Clinical Microbiology. Eds., EH Lennette, A Balows, WJ Hausler, Jr, JP Truant. Washington, DC: American Society for Microbiology, pp 453-458. Whalley P (1967) Bacteriuria of pregnancy. Am J Obstet Gyneco] 97:723.
DIAGN MICROBIOL INFECT DIS 1984;2:193-198
Use of the Becton-Dickinson Urine Culture Tube with the Abbott MS-2 Urine Screening System Paul M. Southern, Jr., and Bobbye Luttrell
Urine specimens were obtained from 312 obstetric outpatients by sterile midstream technique and aliquots placed in both Becton-Dickinson urine culture tubes and sterile conventional tubes. Quantitative cultures were made from each tube, and each tube was screened for bacteria with the Abbott MS-2 urine screening system, The time required to detect bacteriuria was recorded for both specimens. Isolates from specimens containing >50,O00/ml gram-positive cocci or >-lO0,O00/ml gram-negative bacilli were identified and antimicrobial susceptibility tests performed. Delayed ~24 hr) quantitative cultures were done from Becton-Dickinson tubes. By these criteria, 124 urine specimens were positive in both conventional and Becton-Dickinson tubes, gscherichia coil (n = 72), Kiebsiella pneumoniae (n = 20), gnterobacter cloacae (n_ = 8), Proteus mirebilis (n = 4), group B streptococcus (_n = 12), and enterococcus (n = 8) were isolated. Time for detection of positive urine samples was similar in both types of tubes. Delayed cultures had significant numbers of false-positive results. Antimicrobial susceptibility results did not appear to be influenced great/y by Becton-Dickinson tube transport. The MS-2 cannot adequately discriminate cultures containing <50,000 colony-forming units/ml of urine. The Becton-Dickinson tube appears to be compatible for use with the MS-2for purposes of screening for bacteriuria. INTRODUCTION The Becton-Dickinson Urine Culture Kit tube was introduced in an attempt to circumvent logistic problems that frequently make prompt culture or refrigeration of urine specimens difficult to accomplish. It makes use of preservatives (boric acid-glycerol-sodium formate) to suppress bacterial growth in urine without refrigeration for up to 24 hr so that quantitative cultures may be inoculated at a convenient time, yet produce reliable results. Previous studies of the Becton-Dickinson tube have reported variable degrees of reliability of quantitative cultures, with detection rates ranging from 71 to 93% (Guenther and Washington, 1981; Hubbard et al., 1983; Lauer et al., 1979). The Abbott MS-2 apparatus is an automated system that allows screening of urine specimens for significant bacteriuria. It enables the detection of positive cultures within hours, thus permitting negative reports to be issued on the day of collection of specimens. Reports by various investigators have found the MS2 to be 94.3-99.5% accurate in detecting urine specimens containing ->105 organisms/ ml (Godowski and Hodges, 1981; Hoban et al., 1983; McCarthy, 1982; McCarthy et al., 1982; Pezzlo et al., 1982; Szilagyi et al., 1983). Godowski and Hodges (1981) used
From the Department of Pathology, The University of Texas Health Science Center at Dallas, and Clinical Microbiology Laboratory, Parkland Memorial Hospital, Dallas, Texas. Address reprint requests to: Paul M. Southern, Jr., M.D., Department of Pathology, The University of Texas Health Science Center, 5323 Harry Hines Boulevard, Dallas, TX 75235. Received August 31, 1983; revised and accepted December 23, 1983. © 1984 Elsevier Science Publishing Co., Inc. 52 Vanderbilt Avenue, New York, NY 10017
0732-8893/84/$03.00
194
P.M. Southern, Jr., and B. Luttrell
Becton-Dickinson tubes to collect urine specimens subsequently screened by the MS-2, but did not assess whether the preservatives had any effect on the outcome. Only the report of Hubbard et al., (1983) mentioned such an effect. They found a delaying effect on growth of some organisms from Becton-Dickinson tubes. The purpose of the present study was to evaluate the efficacy of collecting urine specimens in Becton-Dickinson tubes and subsequently screening them for bacteriuria with the MS-2.
MATERIALS AND METHODS Urine specimens were obtained from patients attending an obstetrical outpatient clinic for prenatal care. Many patients had symptoms referable to the urinary tract, but others were asymptomatic. Collection of specimens was supervised by a nurse. After preparation of the periurethral area, the patients voided urine that was collected in midstream fashion in a sterile container. Immediately a sample of urine was drawn into a Becton-Dickinson Urine Culture Kit tube and another into a sterile screwcapped tube, routinely used in our hospital for transporting urine to the laboratory for culture. Both tubes were sent to the Clinical Microbiology Laboratory as soon as possible. If transport could not be accomplished within 20 min, the sterile conventional tube was refrigerated. In the laboratory both tubes were streaked with a calibrated quantitative loop onto eosin-methylene blue agar, Columbia CNA blood agar, and blood agar. The quantitative loops were regularly subjected to a quality control procedure and discarded from service if they varied more than 5% from established guidelines. Each tube was also inoculated into an Ampvette of the Abbott MS-2 apparatus for purposes of screening for bacteriuria. The time necessary for the MS2 to judge a urine sample positive was recorded for both specimens. All specimens not determined to be positive by the MS-2 within 6 hr were reported as negative. The numbers and types of organisms isolated on each plate for each specimen were recorded. If the colony count exceeded 50,000/ml for gram-positive cocci or 100,000/ ml for gram-negative bacilli (unmixed cultures), all isolates were identified and antimicrobial susceptibility testing was done (on isolates from both the Becton-Dickinson tubes and conventional tubes). Testing was done by an agar dilution method using a Steers replicator (WaShington and Sutter, 1980) and also with the Abbott MS-2 apparatus (separate testing for organisms isolated from Becton-Dickinson tubes and conventional tubes). The Becton-Dickinson tubes were held an additional 24 hr at room temperature, and a delayed quantitative culture was done for comparison with the original.
RESULTS
Of the 312 urine specimens included in the study, 124 were classified as positive on the basis of colony counts. The organisms recovered and the time required for their assessment as positive by the MS-2 apparatus are shown in Table 1. The median time required for urine specimens to be judged positive was similar for conventional and for Becton-Dickinson collection tubes (overall median time, 95 and 105 min, respectively). No specimens were determined to be positive from conventional tubes and negative from Becton-Dickinson tubes, or vice versa. Specimens deemed negative by the MS-2 were analyzed closely for colony counts and organism types (Table 2). Most represented mixed cultures, or gram-postive cocci in numbers fewer than 25,000/ml. Results of specimens from conventional tubes did not differ significantly from those from Becton-Dickinson tubes. The quantitative
Use of Urine Culture Tube with Urine Screen
195
TABLE 1. Organisms Recovered and Time Required for Detection by Abbott MS-2 Urine Screening System Time (min) Organism (no.)
Type of tube
F.scherichia coli (72)
Mean Median Maximum
Conventional Becton-Dickinson Conventional Becton-Dickinson Conventional Becton-Dickinson Conventional Becton-Dickinson Conventional Becton-Dickinson Conventional Becton-Dickinson
Klebsiella pneumoniae (20) Enterobacter cloacae (8) Proteus mirabilis (4} Group B streptococcus {12] Enterococcus (8)
110 115 109 110 127.5 125 50 60 188 177 162.5 158
70 85 120 115 120 120 50 60 170 160 165 160
280 280 140 140 150 160 60 60 260 260 170 175
cultures from 24-hr delayed streaks from Becton-Dickinson tubes were significantly different in that 40 of 188 specimens had colony counts in excess of 50,000/ml (Table 2). Of these specimens, 19 contained "significant" numbers of bacteria, as defined previously, and would have been reported as positive cultures had that been the only quantitation made. The time required for urine cultures to be judged negative is shown in Table 3. Those specimens containing fewer than 10,000 organisms/ml were occasionally determined to have subthreshold growth sooner in cultures from conventional tubes, whereas this determination was made in those cultures containing more than 10,000 organisms/ml earlier in Becton-Dickinson tubes. Although this information was noted and recorded, no urine specimens with less than threshold growth were removed from the MS-2 in less than 6 hr. Of "negative" specimens with colony counts below 50,000/ml, similar proportions from Becton-Dickinson tubes (116 of 132) and conventional tubes (106 of 120) contained gram-positive cocci. Of "negative" specimens with colony counts greater than 50,000/ml, those from Becton-Dickinson tubes contained two isolates of mixed grampositive cocci, four of mixed gram-negative bacilli, and two of Lactobocillus species; those from conventional tubes contained four isolates of mixed gram-positive cocci, four of mixed gram-negative bacilli, two of Lactobacillus species and two of yeasts.
TABLE 2. Numbers of Specimens with Colony Counts Below Laboratory Standards for Positive Cultures as Determined by the MS-2 by Method of Collection and Enumeration Colony counts of specimens/ml Type of specimen
0-1000
1000-10,000
10,000-50,000
~50,000
Total
Conventional tube Becton-Dickinson tube Delayed streak
54 50 32
82 90 58
38 40 58
14 8 40 a
188 188 188
°Gram-positive cocci or mixed (group B streptococcus, 2), 28; gram-negative bacilli or mixed, 6; grampositive bacilli, 4; yeast, 2.
196
P.M. Southern, Jr., and B. Luttrell
TABLE 3. Time [min) Required for the Abbott MS-2 System to Process IScreen) Urine Specimens by Colony Count a Colony counts of specimens/ml Type of specimen
0-10,000
10,000-50,000
>50,000
Conventional tube Becton-Dickinson tube
259 299
334 238
191 113
aSomeurine specimenswere noted to have subthreshold growth in less than 6 hr, but were not removed from the MS-2 unless deemed positivebefore that time.
Specimens yielding yeasts in conventional tubes also had them isolated from Becton-Dickinson tubes, albeit in smaller numbers. Results of antimicrobial susceptibility testing did not appear to be influenced significantly by transport in the Becton-Dickinson tubes.
DISCUSSION The proportion of urine specimens in this study containing ->10 s organisms/ml (124 of 312, or 39.7%) was relatively high, but is not surprising in view of the patient population surveyed (mostly indigent obstetric patients). Likewise, the population of bacteria recovered was relatively standard for this patient group. Unlike the findings of Hubbard et al., (1983), no significant effect was observed upon the time required for the MS-2 to detect ---105 bacteria/ml of urine in specimens from Becton-Dickinson tubes compared with conventional tubes. This finding may be due in part to the inclusion in their study of several specimens containing Pseudomonas aeruginosa and Staphylococcus epidermidis, organisms for which detection was delayed or absent in Becton-Dickinson tubes. Our patients did not have infections with these species. In specimens that the MS-2 determined to be positive, we saw no discrepancy in quantitative cultures from either conventional or Becton-Dickinson tubes. All 124 specimens positive by the MS-2 had colony counts exceeding 100,000/ml in both tubes. Some specimens had higher counts from the conventional tubes; however, as all counts from the Becton-Dickinson tubes were also above 100,000/ml, no misinterpretation was possible (data not shown). This observation is in modest contrast to the studies of Godowski and Hedges (1981), Hoban et al. (1983), McCarthy (1982), McCarthy et al. (1982), Pezzlo et al. (1982), Szilagyi et al. (1983), who reported a failure rate of 0.5-5.8% in the detection of urine specimens with 10 ~ organisms/ml by the MS-2. Again, this finding may have been due to the patient population in the present study (Kass, 1978; Whalley, 1967). The data with respect to negative specimens are relatively straightforward. No misinterpretations would have resulted from reliance on the original MS-2 readings of urine samples from the Becton-Dickinson tubes. One potentially significant finding with respect to the negative cultures was the discrepant colony counts from the 24-hr delayed cultures from the Becton-Dickinson tubes: 69% had colony counts greater than those from the earlier enumeration. Of such specimens, 19 had colony counts that would have been interpreted as representing significant bacteriuria, had that been the only culture performed. This finding is in contrast to the data of Guenther and Washington (1981), Hubbard et al. (1983), and Lauer et al. (1979), who found lower colony counts after delayed cultures from Becton-Dickinson tubes. Perhaps this result was partly attributable to a change in
Use of Urine Culture Tube with Urine Screen
197
the formulation of the preservatives in the Becton-Dickinson tube (J. J. Mehl, Becton-Dickinson & Co., personal communication). It remains a potentially troublesome problem, however, and should be investigated further. We found no strikingly adverse effects of urine transport in Becton-Dickinson tubes upon subsequent antimicrobial susceptibility testing of significant bacterial isolates. Recently, Stamm et al. (1982) reported data in evaluation of young women with acute lower urinary tract symptoms. Their assessment was that the best diagnostic criterion in this population was a urinary colony count of - 1 0 z coliforms/ml in midstream urine. These findings will necessitate a reevaluation of diagnostic methods used in this population of patients. The methods used in the present study (particularly urine screening with the MS-2) were not sufficiently sensitive to detect bacteriuria at that concentration. Based upon our findings, however, quantitative cultures from the Becton-Dickinson tubes could be used in such evaluations. This concept would require more clinical information to be transmitted to the diagnostic microbiology laboratory, as well as a two-tiered set of standards regarding the constituents of significant bacteriuria. Further study will be required in this area, particularly with respect to refining rapid or automated methods of testing for bacteriuria. Our data suggest that the use of Becton-Dickinson tubes for transport of urine is compatible with subsequent screening for bacterinria with the MS-2. No significant adverse effect was encountered with antimicrobial susceptibility testing. The delayed quantitative culture (after 24 hr) from Becton-Dickinson tubes can be potentially misleading Ithat is, false-positive counts). It is not possible at present to detect bacterial colony counts of approximately 102 organisms/m] with the MS-2; therefore, it is not currently suitable for screening young women in whom acute urethral syndrome is suspected. We wish to thank Barbara McElwee, R.N., and Ms. Alice Gossett for their invaluable assistance in collecting urine specimens and Pattie Pipes for secretarial assistance. Parts of this study were supported by a grant from Becton-Dickinson & Co.
REFERENCES Godowskl KC, Hodges WJ (1981) Accuracy and effect upon clinical workload of the MS-2 urine screen and antibiotic susceptibility system. Lab Med 12:758. Guenther KL, Washington JAII (1981) Evaluation of the B-D urine culture kit. J. C/in Microbiol 14:628. Hoban DJ, Koss JC, Gratton CA, Ronald AR (1983) Urine screening with the MS-2. J Clin Microbiol 17:1061. Hubbard WA, Shalis PJ, McClatchey KD (1983) Comparison of the B-D urine culture kit with a standard culture method and with the MS-2. ] Clin Microbiol 17:327. Kass EH (1978) Horatio at the orifice: Significance of bacteriuria. I Infect Dis 138:546. Lauer BA, Relier LB, Mirrett S (1979) Evaluation of preservative fluid for urine collection for culture. I Clin Microbiol 10:42. McCarthy LR (1982) Evaluation of the MS-2 system for the detection of bacteriur/a. In Rapid Methods and Automation in Microbiology. Ed., RC Tilton. Washington, DC: American Society for Microbiology, pp 316-320. McCarthy LR, Gavan TL, Robson J, Corlett C (1982) Evaluation of the MS-2 urine screening method for detection of bacteriuria. ! Clin Microbiol 16:250. Pezzlo MT, Tan GL, Peterson EM, de la Maza LM (1982) Screen/rig of urine cultures by three automated systems. J Clin Microbiol 15:468. Stature WE, Counts GW, Running KR, Fihn S, Turck M, Holmes KK (1982) Diagnosis of coliform infection in acutely dysuric women. N Eng/I Med 307:463.
198
P.M. Southern, Jr., and B. Luttrell
Szilagyi G, Ailing V, Karmen A (1983) Comparative study of two methods for rapid detection of clinically significant bacteriuria. J Clin Lab Automat 3:117. Washington JAII, Sutter VL (1980) Dilution susceptibility test: Agar and macro-broth dilution procedures. In Manual of Clinical Microbiology. Eds., EH Lennette, A Balows, WJ Hausler, Jr, JP Truant. Washington, DC: American Society for Microbiology, pp 453-458. Whalley P (1967) Bacteriuria of pregnancy. Am J Obstet Gyneco] 97:723.