Multiplication of contaminant bacteria in urine and interpretation of delayed culture

The impact of Boric Acid tubes on quantitative urinary bacterial cultures in hospitalized patients

INTRODUCTION

The accuracy of urine culture results can be affected by pre-analytical factors such as transport delays and storage conditions. The objectives of this study were to analyze urine collection practices and assess the impact of introducing boric acid tubes for urine collection on quantitative urinary bacterial cultures of hospitalized patients in medical wards.

METHODS

A quasi-experimental pre-post study conducted in an acute care facility. In the pre-intervention phase (2020-2021), urine samples were transported without preservatives at room temperature. In 2022 (post-intervention), we transitioned to boric acid transport tubes, evaluating its effect on significant bacterial growth (≥ 105 CFU/ml). Bivariate and multivariate analyses identified predictors of culture positivity.

RESULTS

Throughout the duration of the study, a total of 12,660 urine cultures were analyzed. Date and time documentation was complete for 38.3% of specimens. Culture positivity was higher with longer processing times: positivity was 21.3% (220/1034) when specimens were processed within 4 h, 28.4% (955/3364) when processed in 4-24 h, and 32.9% (137/417) when processed after 24 h (p < 0.0001). For 4-24-hour processing, positivity decreased from 30.4% (704/2317) pre-intervention to 24.0% (251/1047) post-intervention (p < 0.001), with no significant changes in < 4 or ≥ 24-hour specimens. Stratified analysis by processing time revealed that the intervention was associated with reduced positivity only in cultures processed within 4-24 h (OR 0.80, 95% CI 0.67-0.94; p = 0.008).

CONCLUSION

The introduction of boric acid transport tubes predominantly influenced cultures transported within a 4-24-hour window. This presents an opportunity to improve urine tract infection diagnostic practices in healthcare settings.

Sampling of urine for diagnosing urinary tract infection in general practice - First-void or mid-stream urine?

OBJECTIVE

To study 1) whether the accuracy of point-of-care (POC) urine tests (dipstick, phase-contrast microscopy and culture) differs when performed on first-void urine (FVU) compared to mid-stream urine (MSU), and 2) if a delay of analysis up to four hours affects the accuracy of POC tests when performed on urine from symptomatic of urinary tract infection (UTI), non-pregnant women in general practice.

DESIGN

Prospective diagnostic study using paired samples. Setting/Intervention: Three general practices in Copenhagen. Each woman delivered FVU and MSU samples from the same void. As a reference standard, 8 ml of MSU was sent for culture at the Microbiology Department.

PATIENTS

117 women with one or more symptoms of UTI.

MAIN OUTCOME MEASURES

Sensitivity, specificity and agreement with the reference standard of FVU and MSU with different time delays (zero vs. one vs. four hours) as compared to reference standard (MSU at time zero in boric acid tubes).

RESULTS

All three POC tests performed on MSU were significantly more in agreement with the reference than when performed on FVU when analysis was done immediately. The error rate was 16% for MSU vs. 23% for FVU with POC culture, 27% vs. 40% with microscopy and 25% vs. 33% with dipstick testing. Delay of analysis up to four hours did not decrease agreement with the reference. Conclusion/Implication: MSU samples should be used in general practice for optimal accuracy of POC tests. Analysis can be delayed up to four hours. Key points Point-of-care tests (dipstick testing, microscopy and culture) for diagnosing urinary tract infection performed on mid-stream urine samples are significantly more accurate than when performed on first-void urine samples. Delay of analysis up to four hours did not decrease the accuracy of any of the point-of-care tests. Point-of-care culture was more accurate than dipstick and microscopy both when performed on mid-stream urine and first-void urine The main contaminant in first-void urine samples was Enterococci spp., which contributed to the majority of false positives.

Comparison of clinical performance of commercial urine growth stabilization products

INTRODUCTION

Urine specimens for quantitative culture for the diagnosis of urinary tract infection may be unreliable due to bacterial overgrowth within 4 h after collection, at room temperature. Because specimen transportation may take longer than 4 h, urine preservatives may reduce overgrowth. Further evidence is needed to support a recommendation for use of preservative and to compare preservative products.

METHODS

Consecutive midstream urine specimens submitted for culture were quantitatively cultured on receipt and then inoculated into 3 storage conditions [BD Urine Vacutainer (BD), Copan UriSwab (US), and refrigeration, with a room temperature control] for 72 h, with quantitative culture performed every 24 h. Odds ratio for significant growth interpretation was reported.

RESULTS

Ninety-five of 501 (19.0%) urine specimens demonstrated significant growth. Within 24 h of storage, unpreserved urine at room temperature demonstrated a significantly increased odds ratio for significant growth as compared to preserved urine, and urine in refrigeration demonstrated similar odds ratio for significant growth as compared to preserved. There was no significant difference between the performance of US and BD. Over 48 and 72 h of storage, odds ratio for significant growth further increased.

CONCLUSIONS

Preservation performed similarly to refrigeration. Preserved urine demonstrated a doubling in odds ratio for significant growth after 24 h. This increase may negatively impact antibiotic treatment decisions.

Laboratory diagnosis of urinary tract infections: Towards a BILULU consensus guideline

Urinary tract infections (UTI) are very common throughout life and account for the majority of the workload in the clinical microbiology laboratory. Clear instructions for the interpretation of urine cultures by the laboratory technicians are indispensable to obtain standardized, reliable, and clinically useful results. In literature, there is often a lack of evidence-based practice in processing urinary samples in the laboratory. In this consensus document, the BILULU Study Group presents a practical approach for the implementation of existing guidelines for the culture of urine in the microbiology laboratory and offers answers for issues where no clear solution is available in the guidelines.

Evaluation of the BD Vacutainer Plus Urine C&S Preservative Tubes compared with nonpreservative urine samples stored at 4°C and room temperature

OBJECTIVES

The stability of urine specimens submitted for culture remains a challenge for many laboratories because of delays in specimen transport. We evaluated the usefulness of BD Vacutainer Plus Urine C&S Preservative Tube in ensuring specimen stability.

METHODS

Clinical urine specimens collected in sterile collection cups (n = 110) were plated onto sheep blood and MacConkey agar following standard laboratory procedures guidelines. Thereafter, specimens were divided into 3 storage conditions: nonpreservative, refrigerated; nonpreservative, room temperature (RT); BD Vacutainer Plus Urine C&S Preservative Tube, RT. For each sample type, additional cultures were set up at 2, 4, 24, and 48 hours.

RESULTS

Initially, 18 specimens had no growth, 32 showed mixed skin flora, and 60 yielded at least 1 uropathogen. Increased colony counts of uropathogens were observed for nonpreserved urine samples stored at RT; these changes were statistically significant. Minor differences between refrigerated urine samples and BD Vacutainer Plus Urine C&S Preservative Tube samples were seen but were not statistically significant.

CONCLUSIONS

The use of preservative-containing collection tubes is desirable to ensure specimen stability when prompt processing or refrigeration is not feasible.

Investigations of the microbial transformation of cortisol to prednisolone in urine samples

Doping control samples are normally collected under non-sterile conditions and sometimes, storage and transportation are influenced by parameters such as the temperature. Therefore, microbial contamination and subsequent alteration of a sample's composition are possible. Studies regarding sample collection in cattle breeding have already shown enzymatic transformation of endogenous testosterone to boldenone causing false-positive findings. The aim of the present study was to investigate whether positive doping cases with the synthetic corticosteroids prednisolone and prednisone may result from microbial transformation of the endogenous corticosteroids cortisol and cortisone, respectively. A method comprising parameters such as pH values and screening results for synthetic glucocorticosteroids as well as incubation experiments followed by liquid chromatographic and mass spectrometric analysis was employed to test for contaminating germs with Δ(1)-dehydrogenase activity. Over 700 urine samples comprising inpatient and doping control specimens were investigated. In none of them, 1,2-dehydrogenating activity was confirmed. These findings are in accordance with other studies. However, the problem of microbial alteration of doping control specimens with special respect to 1,2-dehydrogenation must not be underestimated. Article from a special issue on steroids and microorganisms.

The effect of boric acid on bacterial culture of canine and feline urine

OBJECTIVE

To identify the optimal method of submission of canine and feline urine for bacterial culture.

METHODS

Cystocentesis samples from 250 animals (200 dogs, 50 cats) suspected of having urinary tract infections were collected. The reference aliquot, without preservative, was processed on site within 2 hours. Two further aliquots (one without preservative, one with boric acid) were stored at room temperature for up to 7 hours and then posted by guaranteed next day delivery to a commercial laboratory for analysis.

RESULTS

Forty-seven of the samples were positive on culture in the reference test. There was no significant difference between reference test results and those of samples posted without preservative (P=0·39), but samples posted in boric acid were significantly less likely to give a positive result (P=0·01). Samples posted without preservative had a sensitivity of 82% and a specificity of 98%; for boric acid, sensitivity was 73% and specificity 99%.

CLINICAL SIGNIFICANCE

Postal urine samples should be submitted to the laboratory in a plain sterile tube.

Laboratory diagnosis of urinary tract infections in adult patients

Urinary tract infections (UTIs) are among the most common bacterial infections and account for a significant part of the workload in clinical microbiology laboratories. Enteric bacteria (in particular, Escherichia coli) remain the most frequent cause of UTIs, although the distribution of pathogens that cause UTIs is changing. More important is the increase in resistance to some antimicrobial agents, particularly the resistance to trimethoprim-sulfamethoxazole seen in E. coli. Physicians distinguish UTIs from other diseases that have similar clinical presentations with use of a small number of tests, none of which, if used individually, have adequate sensitivity and specificity. Among the diagnostic tests, urinalysis is useful mainly for excluding bacteriuria. Urine culture may not be necessary as part of the evaluation of outpatients with uncomplicated UTIs, but it is necessary for outpatients who have recurrent UTIs, experience treatment failures, or have complicated UTIs, as well as for inpatients who develop UTIs.

The effect of specimen processing delay on borate urine preservation

AIM

To investigate the effect on urine culture results and their clinical interpretation of delaying the processing of urine samples in which boric acid had been used as a preservative.

METHODS

792 mid-stream specimens of urine from patients attending their general practitioner were received in borate containing plastic jars. The specimens were cultured upon receipt, stored at room temperature, and then recultured the following morning.

RESULTS

After overnight delayed culture, the results were altered in 16% of samples and the clinical interpretation of these findings differed in 8% of specimens. In 28 samples (3.5%) the bacterium isolated on initial culture was not the same as that obtained by culture after overnight storage.

CONCLUSIONS

Boric acid urine preservation used for overnight delayed processing of samples is associated with a significant alteration in culture results and the attendant clinical interpretation of such specimens. Rapid transportation/processing of urine specimens must remain the optimum procedure.

Bacteriostatic and bactericidal actions of boric acid against bacteria and fungi commonly found in urine

Boric acid has been used for over 20 years to preserve urine while in transit for bacteriological examination. It has been suggested that it may be toxic for some urinary pathogens. To investigate this several strains of bacteria and fungi commonly found in urine were exposed to different concentrations of boric acid in nutrient broth. Viable counts were made at the outset and at intervals for up to 24 hours at room temperature to detect bacteriostatic or bactericidal effects. At concentrations between 10 and 20 g/l boric acid was bacteriostatic or fungistatic for very nearly all the common urinary pathogens. At 10 g/l boric acid was weakly bactericidal for some strains of Acinetobacter calcoaceticus and Pseudomonas aeruginosa, though higher concentrations were bacteriostatic only. Group B streptococci varied in their response to boric acid, but for most of them 10 or 20 g/l was satisfactorily bacteriostatic. It is concluded that boric acid is rarely toxic, and when it is, the effect is usually sufficiently delayed to be of only theoretical importance.

Boric acid converts urine into an effective bacteriostatic transport medium

Results of an experiment designed to assess the usefulness of boric acid for preserving urine before its bacteriological examination are reported. Boric acid at a concentration of 20 g/l was found to be usefully bacteriostatic, largely eliminating the false positive results obtained with unpreserved specimens when delay before culture was more than 90 min. The effect lasted for up to 48 h. There was no evidence that borate is toxic to the urinary pathogens encountered in naturally infected urine. Borate also preserves white blood cells in urine and thereby marginally improved the diagnosis of pyuria. The results confirm that boric acid may with benefit be added to bottles used for transporting specimens of urine to the laboratory.

A urine preservative system to maintain bacterial counts. A laboratory and clinical evaluation

The urinary tract is a common site of infection in the hospitalized, institutionalized, or ambulatory patient population. Ideally, urine should be cultured immediately or refrigerated up to 24 hours for quantitative examination for microorganisms. In the evaluation of patients at their homes or in long-term care facilities, rapid plating or refrigeration may not be practical. This is also true when evaluating small children in whom external collection devices are required to obtain a specimen. Because of these limitations, we evaluated a urine preservative and transport system, the Sage Products Urine Culture Tube, in a study of 1469 clinical specimens. This tube utilizes boric acid (1.1% final concentration) as a preservative. The Urine Culture Tube was easy to use and was as effective as refrigeration in maintaining bacterial counts. This system may be particularly useful where rapid transport or refrigeration is limited.

Comparison of the B-D urine culture kit with a standard culture method and with the MS-2

A total of 100 random clinical urine specimens were divided and used to compare Becton, Dickinson & Co. B-D Urine Culture Kit-treated urine (BDU) with refrigerated urine (RU). Each RU-BDU pair was cultured with the standard calibrated loop-plate method and also screened with the Abbott Laboratories MS-2 system at 0, 5, and 24 h. An additional 158 positive urine specimens containing greater than 10(5) CFU/ml were tested by standard culturing and MS-2 at 0 and 24 h. In addition, growth curves were run for Escherichia coli containing RU-BDU pairs at 0 and 24 h, and MS-2 detection time frequencies were analyzed. Culture results showed few changes in colony counts at 0 and 5 h for RU and BDU specimens. At 24 h, there were decreased colony counts for 7.0% of RU and 17.7% of BDU specimens. MS-2 results showed detection rates at 0 h of 100% for RU and 82.9% for BDU specimens and at 24 h of 91.1% for RU and 63.3% for BDU specimens. The organisms most frequently missed at 24 h were E. coli, Pseudomonas aeruginosa, and Staphylococcus epidermidis. Growth curve analysis showed a 1-h delay of logarithmic growth in BDU specimens. MS-2 detection time analysis showed delayed positive reports owing to be extended detection time for BDU specimens. The B-D Urine Culture Kit is a convenient transport system; however, some difficulty in recovering organisms at 24 h with the standard culture method and increased difficulty with the MS-2 system were recognized.

Evaluation of preservative fluid for urine collected for culture

Immediate culture or refrigeration of urine is recommended, but not always practical. Therefore, we evaluated the Becton-Dickinson Urine Culture Kit containing a boric acid-glycerol-sodium formate preservative in a study of 1,000 clinical urine specimens. Each specimen was cultured a total of four times by the surface streak technique with a 0.001-ml calibrated loop. After an initial reference culture (culture 1), a portion of urine was poured into a clean nonsterile paper cup, aspirated into a urine transport tube, and recultured immediately (culture 2). The original specimen cup was refrigerated for 18 to 24 h (culture 3), and the urine transport tube was held at room temperature for 18 to 24 h (culture 4) before repeat cultures. Eighty-eight of the initial reference cultures were positive (pure growth of greater than 10(5) bacteria per ml). Eighty-two (93.2%) of the 88 specimens positive on the reference culture were also positive after refrigeration or holding at room temperature in the transport tube for 24 h. There was one false-positive culture from refrigerated urine but none from the transport tube. Mixing of urine in a nonsterile container did not introduce detectable contamination. We conclude that the Becton-Dickinson Urine Culture Kit maintains a stable bacterial population in urine for up to 24 h as reliably as refrigeration. Urine for culture may be collected in a nonsterile container if it is immediately aspirated into the transport tube so that contaminants are not allowed to multiply.