Rapid screening of urine for bacteria and cells by using a catalase reagent

An improved method for measuring catalase activity in biological samples

Catalase (CAT) is an important enzyme that protects biomolecules against oxidative damage by breaking down hydrogen peroxide (H2O2) into water and oxygen. CAT is present in all aerobic microbes, animals, and plants. It is, however, absent from normal human urine but can be detected in pathological urine. CAT testing can thus help to detect such urine. This study presents a novel spectrophotometric method for determining CAT activity characterized by its simplicity, sensitivity, specificity, and rapidity. The method involves incubating enzyme-containing samples with a carefully chosen concentration of H2O2 for a specified incubation period. Subsequently, a solution containing ferrous ammonium sulfate (FAS) and sulfosalicylic acid (SSA) is added to terminate the enzyme activity. A distinctive maroon-colored ferrisulfosalicylate complex is formed. The formation of this complex is a direct result of the reaction between FAS and any residual peroxide present. This leads to the generation of ferric ions when coordinated with SSA. The complex has a maximum absorbance of 490 nm. This advanced method eliminates the need for concentrated acids to stop CAT activity, making it safer and easier to handle. A comparative analysis against the standard ferrithiocyanate method showed a correlation coefficient of 0.99, demonstrating the new method's comparable effectiveness and reliability. In conclusion, a simple and reliable protocol for assessing CAT activity, which utilizes a cuvette or microplate, has been demonstrated in this study. This interference-free protocol can easily be used in research and clinical analysis with considerable accuracy and precision.

Detection of bacteriuria and bacteremia in newborn calves by a catalase-based urine test

BACKGROUND

Bacteremia occurs frequently in newborn calves. The predictive value of clinical signs is low, suggesting the use of calf-side diagnostic tests.

OBJECTIVES

To investigate testing of urine catalase activity (Uriscreen test) for bacteriuria and bacteremia detection.

ANIMALS

Five colostrum-free calves and 3 colostrum-fed control calves.

METHODS

Controlled experimental trial. Colostrum-free calves were inoculated PO with Escherichia coli O78+. A clinical score was established to define the onset of the illness. Blood and urine (cystocentesis) samplings and cultures, and Uriscreen tests, were performed 4-6 times from inoculation to death. Three control calves received the same management as 3 inoculated calves, but with colostrum and without inoculation.

RESULTS

Bacteremia was demonstrated in all of the inoculated colostrum-free calves and in none of the control calves. The E. coli O78+ strain, E. coli, and Klebsiella spp. were recovered from 4/5, 5/5, and 2/5 inoculated colostrum-free calves, respectively. Urine cultures were negative for the 2 groups at the start of the experiment; 5/5 colostrum-deprived inoculated calves were positive for E. coli thereafter whereas 3/3 controls remained negative. Concordance of Uriscreen tests with bacteremia and bacteriuria was 0.86 and 0.88, respectively. Kappa value of agreement between Uriscreen and bacteremia and bacteriuria was 0.73 and 0.76, respectively. Sensitivity of Uriscreen for bacteremia and bacteriuria was 80.0 and 86.6%, respectively, and specificity was 92.8 and 88.8%, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

The results suggest that Uriscreen can be used for detection of bacteremia in neonatal calves in connection with a constant bacteriuria.

Detection of volatile metabolites produced by bacterial growth in blood culture media by selected ion flow tube mass spectrometry (SIFT-MS)

To achieve faster bacteremia diagnosis, selected ion flow tube mass spectrometry (SIFT-MS) measured metabolic gases in the headspaces of BacT/ALERT blood culture bottles. Pseudomonas aeruginosa, Streptococcus pneumoniae, Escherichia coli, Staphylococcus aureus and Neisseria meningitidis growth and trace gas patterns were detected from 10 colony forming units after 6 h.

Elastase: a predictive marker of inflammation and/or infection

The present study was undertaken to estimate elastase in biological fluids and assess its usefulness as an indicator of inflammation/infection. Elastase was measured in seminal plasma, serum, urine, and cervical specimens using a specific substrate and was expressed in arbitrary units (AU). It was found to be stable over a period of 3 weeks. The intra- and interassay variation of elastase assay was between 2.3 to 6.8% and 7.3 to 9.9%, respectively. The assay was validated by comparing it with other methods that are available for the detection of infections. Sensitivity of the assay indicating inflammation/infection in these samples varied between 70.9 to 87.3%. The results obtained suggest that the presence of elastase in specimens may be used as a nonspecific indicator and could be used to screen inflammation/infection in a limited resource setting.

The urine dipstick test useful to rule out infections. A meta-analysis of the accuracy

BACKGROUND

Many studies have evaluated the accuracy of dipstick tests as rapid detectors of bacteriuria and urinary tract infections (UTI). The lack of an adequate explanation for the heterogeneity of the dipstick accuracy stimulates an ongoing debate. The objective of the present meta-analysis was to summarise the available evidence on the diagnostic accuracy of the urine dipstick test, taking into account various pre-defined potential sources of heterogeneity.

METHODS

Literature from 1990 through 1999 was searched in Medline and Embase, and by reference tracking. Selected publications should be concerned with the diagnosis of bacteriuria or urinary tract infections, investigate the use of dipstick tests for nitrites and/or leukocyte esterase, and present empirical data. A checklist was used to assess methodological quality.

RESULTS

70 publications were included. Accuracy of nitrites was high in pregnant women (Diagnostic Odds Ratio = 165) and elderly people (DOR = 108). Positive predictive values were >/=80% in elderly and in family medicine. Accuracy of leukocyte-esterase was high in studies in urology patients (DOR = 276). Sensitivities were highest in family medicine (86%). Negative predictive values were high in both tests in all patient groups and settings, except for in family medicine. The combination of both test results showed an important increase in sensitivity. Accuracy was high in studies in urology patients (DOR = 52), in children (DOR = 46), and if clinical information was present (DOR = 28). Sensitivity was highest in studies carried out in family medicine (90%). Predictive values of combinations of positive test results were low in all other situations.

CONCLUSIONS

Overall, this review demonstrates that the urine dipstick test alone seems to be useful in all populations to exclude the presence of infection if the results of both nitrites and leukocyte-esterase are negative. Sensitivities of the combination of both tests vary between 68 and 88% in different patient groups, but positive test results have to be confirmed. Although the combination of positive test results is very sensitive in family practice, the usefulness of the dipstick test alone to rule in infection remains doubtful, even with high pre-test probabilities.

The validity of the uriscreen test for early detection of urinary tract infection in children

OBJECTIVE

To determine the validity of the Uriscreen, a rapid diagnostic test based on the detection of urine catalase for the early detection of urinary tract infection (UTI) in children, compared with standard urinalysis and dipstick tests. STUDY DESIGN. Cross-sectional study.

STUDY POPULATION

Children 1 month to 17 years of age who presented to the emergency department of a pediatric tertiary care center between March and November of 1996 with symptoms suggestive of UTI.

METHODS

Urine specimens obtained from a random sample of 121 patients were evaluated simultaneously for possible UTI by Uriscreen (catalase test), urinalysis (microscopic pyuria), dipstick (leukocyte esterase and nitrite), and quantitative urine culture. All specimens were collected by one of three sterile techniques (midstream void technique, bladder catheterization, or suprapubic aspiration), as appropriate for age, and tested immediately. Using the quantitative urine culture as the gold standard (reference test), the sensitivity, specificity, and positive and negative predictive values of all the screening tests were determined and compared. Age, sex, temperature, presenting symptoms, and method of urine collection were recorded for each participant.

RESULTS

Of the 121 patients, 35 (28.9%) had positive culture results: 30 girls (85.7%) and 5 boys (14.3%). Compared with urinalysis and dipstick tests, Uriscreen had the highest sensitivity (100% vs 88.6% and 97.1%, respectively) and the highest negative predictive value (100% vs 95% and 98.6%, respectively), but the poorest specificity (68.6% vs 88.4% and 82.5%, respectively) and positive predictive value (56.4% vs 75.6% and 69.4%, respectively).

CONCLUSIONS

The clinical use of Uriscreen for the presumptive diagnosis of UTI in children is limited and not significantly superior to urinalysis or the dipstick test. However, because of its 100% sensitivity and negative predictive value and its ease of use, rapidity, and low cost, it is recommended highly for ruling out the diagnosis of UTI. In laboratories, a negative Uriscreen result may prevent the need for performing expensive urine cultures.

A comparison of the API Uriscreen with the Vitek Urine Identification-3 and the leukocyte esterase or nitrite strip as a screening test for bacteriuria

The API Uriscreen is a rapid urine-screening test based on the detection of catalase activity present in somatic cells and in many of the bacteria commonly causing urinary tract infections. Of 487 routine, outpatient urine specimens processed by conventional quantitative culture, API Uriscreen, Vitek UID-3 panel, and a leukocyte esterase-nitrite strip, 142 had no growth. Of 336 urine specimens with > or = 10(3) colony-forming units (CFU)/ml, 79 were considered to be indicative of possible or probable urinary tract infection (Cumitech 2A). The sensitivity and specificity of the API Uriscreen for the detection of bacteriuria at > or = 10(5) CFU/ml were 62% and 85%, those of the leukocyte esterase-nitrite strip was 61% and 82%, those of the Vitek UID-3 panel were 91% and 66%. When bacteriurias were classified into possibly or probably indicative of urinary tract infection, the sensitivity and specificity of the API Uriscreen at > or = 10(5) CFU/ml were 87% and 78%, those of the leukocyte esterase-nitrite were 84% and 76%, those of the Vitek UID-3 were 93% and 55%. In this study, we consider the API Uriscreen did not have significant advantages over the leukocyte esterase-nitrite strip.

Two rapid urine screens for detection of bacteriuria: an evaluation

Five hundred twenty-five random clean catch urine specimens, collected from 339 adult females, 137 adult males, and 49 pediatric patients, were screened for the presence of bacteriuria with the Uriscreen catalase test and with the Chemstrip 2 LN dipstick. Quantitative cultures were performed on all specimens. The sensitivity, specificity, positive predictive value, and negative predictive value for the catalase test, with 10(5) CFU/ml as the threshold for significant bacteriuria, were 91.3%, 72.3%, 33.7%, and 98.0%, respectively. Values for the dipstick were 83.9%, 77.9%, 43.7%, and 96.0%. When 10(4) CFU/ml was used as the threshold, the catalase test had a sensitivity of 89.2%, specificity of 70.4%, positive predictive value of 37.3%, and a negative predictive value of 97.0%. Values for the dipstick at that level were 82.3%, 77.5%, 48.6%, and 94.8%. While the catalase test was more sensitive than the dipstick, it was our opinion that high rates of false-negatives associated with these methods negated the convenience of these fast and simple urine screens.

Initial testing of a novel urine culture device

The Diaslide urine culture device consists of a hinged case containing two opposing agar media separated by a sampler with a handle at one end and two bent sampler tips at the opposite end. The tips of the sampler are first dipped into the urine. The sampler is then pulled out through the casing, simultaneously inoculating both agar surfaces with a streaking dilution. As a result, individual colonies can be observed even when bacterial concentrations exceed 10(6) CFU/ml. The number of colonies on the Diaslide correlated linearly with CFU per milliliter as determined by dilution plating. The clinical performance of the Diaslide was compared with those of ordinary dipslides and conventional cultures with a sample of 473 prescreened hospital urine specimens. The sensitivity, specificity, and positive predictive value of Diaslide versus those of culture at the 10(4)-CFU/ml cutoff level were 97.5, 98.3, and 98.3%, respectively, compared with 98.8, 95.7, and 97.2%, respectively, for dipslide versus culture. Similar results were found at the 10(5)-CFU/ml cutoff level. Only 5.5% of the Diaslides required subculturing, compared with 14.7 and 9.4% of the dipslides and conventional cultures, respectively. The Diaslide proved more convenient than an ordinary dipslide for sampling low volumes of urine. These data suggest that the Diaslide is a simple, effective device for culturing of urine specimens.

Detection of bacteriuria and pyuria by URISCREEN a rapid enzymatic screening test

A multicenter study was performed to evaluate the ability of the URISCREEN (Analytab Products, Plainview, N.Y.), a 2-min catalase tube test, to detect bacteriuria and pyuria. This test was compared with the Chemstrip LN (BioDynamics, Division of Boehringer Mannheim Diagnostics, Indianapolis, Ind.), a 2-min enzyme dipstick test; a semiquantitative plate culture method was used as the reference test for bacteriuria, and the Gram stain or a quantitative chamber count method was used as the reference test for pyuria. Each test was evaluated for its ability to detect probable pathogens at greater than or equal to 10(2) CFU/ml and/or greater than or equal to 1 leukocyte per oil immersion field, as determined by the Gram stain method, or greater than 10 leukocytes per microliter, as determined by the quantitative count method. A total of 1,500 urine specimens were included in this evaluation. There were 298 specimens with greater than or equal 10(2) CFU/ml and 451 specimens with pyuria. Of the 298 specimens with probable pathogens isolated at various colony counts, 219 specimens had colony counts of greater than or equal to 10(5) CFU/ml, 51 specimens had between 10(4) and 10(5) CFU/ml, and 28 specimens had between 10(2) and less than 10(4) CFU/ml. Both the URISCREEN and the Chemstrip LN detected 93% (204 of 219) of the specimens with probable pathogens at greater than or equal to 10(5) CFU/ml. For the specimens with probable pathogens at greater than or equal to 10(2) CFU/ml, the sensitivities of the URISCREEN and the Chemstrip LN were 86% (256 of 298) and 81% (241 of 298), respectively. Of the 451 specimens with pyuria, the URISCREEN detected 88% (398 of 451) and Chemstrip LN detected 78% (350 if 451). There were 204 specimens with both greater than or equal to 10(2) CFU/ml and pyuria; the sensitivities of both methods were 95% (193 of 204) for these specimens. Overall, there were 545 specimens with probable pathogens at greater than or equal to 10(2) CFU/ml and/or pyuria. The URISCREEN detected 85% (461 of 545), and the Chemstrip LN detected 73% (398 of 545). A majority (76%) of the false-negative results obtained with either method were for specimens without leukocytes in the urine. There were 955 specimens with no probable pathogens or leukocytes. Of these, 28% (270 of 955) were found positive by the URISCREEN and 13% (122 of 955) were found positive by the Chemstrip LN. A majority of the false-positive results were probably due, in part, to the detection of enzymes present in both bacterial and somatic cells by each of the test systems. Overall, the URISCREEN is rapid, manual, easy-to-perform enzymatic test that yields findings similar to those yielded by the Chemstrip LN for specimens with both greater than or equal to 10(2) CFU/ml and pyuria or for specimens with greater than or equal to 10(5) CFU/ml and with or without pyuria. However, when the data were analyzed for either probable pathogens at less 10(5) CFU/ml or pyuria, the sensitivity of the URISCREEN was higher (P less than 0.05).