An evaluation of a leukocyte esterase/nitrite test strip and a bioluminescence assay for detection of bacteriuria

An Intact Cell Bioluminescence-Based Assay for the Simple and Rapid Diagnosis of Urinary Tract Infection

Urinary tract infection (UTI) is one of the most common infections, accounting for a substantial portion of outpatient hospital and clinic visits. Standard diagnosis of UTI by culture and sensitivity can take at least 48 h, and improper diagnosis can lead to an increase in antibiotic resistance following therapy. To address these shortcomings, rapid bioluminescence assays were developed and evaluated for the detection of UTI using intact, viable cells of Photobacterium mandapamensis USTCMS 1132 or previously lyophilized cells of Photobacterium leiognathi ATCC 33981™. Two platform technologies-tube bioluminescence extinction technology urine (TuBETUr) and cellphone-based UTI bioluminescence extinction technology (CUBET)-were developed and standardized using artificial urine to detect four commonly isolated UTI pathogens-namely, Escherichia coli, Proteus mirabilis, Staphylococcus aureus, and Candida albicans. Besides detection, these assays could also provide information regarding pathogen concentration/level, helping guide treatment decisions. These technologies were able to detect microbes associated with UTI at less than 105 CFU/mL, which is usually the lower cut-off limit for a positive UTI diagnosis. Among the 29 positive UTI samples yielding 105-106 CFU/mL pathogen concentrations, a total of 29 urine specimens were correctly detected by TuBETUr as UTI-positive based on an 1119 s detection window. Similarly, the rapid CUBET method was able to discriminate UTIs from normal samples with high confidence (p ≤ 0.0001), using single-pot conditions and cell phone-based monitoring. These technologies could potentially address the need for point-of-care UTI detection while reducing the possibility of antibiotic resistance associated with misdiagnosed cases of urinary tract infections, especially in low-resource environments.

A simple spectrophotometric assay for urinary leukocyte esterase activity

We have developed a sensitive spectrophotometric method for assaying urinary leukocyte esterase activity by employing a synthetic substrate, N-toluene sulfonyl indoxyl alanine ester. This kinetic assay can be performed with a small aliquot of urine, by following the change in absorbance of the chromophore at 385 nm. It is rapid and specific for leukocyte esterase and therefore can be used in the early diagnosis of urinary tract infection.

Clinical relevance of culture versus screens for the detection of microbial pathogens in urine specimens

The use of screens to detect "significant levels" of pathogenic microorganisms in urine specimens offers the advantages of both rapidly reporting results and controlling costs. Many of these screens, however, are insensitive at microbial counts below 10(5) colony-forming units (CFU)/ml of urine. It is increasingly apparent that patients with almost any type of urinary tract infection (except for most patients who are asymptomatic or who have pyelonephritis) may have urine concentrations of pathogens as low as 10(2) to 10(3) CFU/ml. This review documents factors that can contribute to diminished concentrations of microorganisms in urine, lists patient populations in whose urine microorganisms in concentrations well below 10(5) CFU/ml have been associated with infection, and makes recommendations for selection of laboratory tests, including rapid screens, for the diagnosis and management of urinary tract infections.

Rapid detection methods in microbiology: are they right for your office?

This article discusses some of the direct test methods for diagnosing Group A streptococcal pharyngitis, urinary tract infection, and the three most common sexually transmitted diseases: gonorrhea, Chlamydia, and Herpes simplex virus infection. Emphasis is placed on their practicality for the office setting as well as the limitations of the test methods in various patient populations.

The usefulness of screening tests for pyuria in combination with culture in the diagnosis of urinary tract infection

A prospective study was conducted to examine the usefulness of screening tests for pyuria in combination with culture in the diagnosis of urinary tract infection (UTI) in outpatients. Midstream urine specimens were collected from 340 patients seen in the emergency treatment center (ETC) and were examined for pyuria using the chamber count method and the Leukocyte Esterase Dipstick test (LE; Bio Dynamics, Indianapolis, IN). All specimens were cultured quantitatively using both 0.01 ml and 0.001 ml calibrated bacteriologic loops. A total of 100 UTIs, defined by combined clinical and laboratory critera, were identified. Sixty-four (64%) infections were identified by culture using the standard interpretive breakpoint of greater than or equal to 10(5) CFU/ml and an additional 36 (36%) were detected using the low-count interpretive breakpoint of greater than or equal to 10(3) CFU/ml. We found pyuria detection by either the chamber count method or the LE test to be extremely useful in directing subsequent culture efforts. By using either of the tests for pyuria to determine the significance of low-count bacteriuria (10(3) - less than 10(5) CFU/ml) we were able to achieve maximum sensitivity (92%-99%) and specificity (99.2-99.6%) for the diagnosis of UTI while minimizing the number of specimens in which low numbers of organisms must be evaluated.

Screening for bacteriuria with the LN strip test

Recently, the LN strip test was introduced for purposes of rapid screening of urine specimens for bacteriuria. The LN strip test permits detection of urinary leukocyte esterase and nitrite. A total of 2,481 unselected urine specimens from three tertiary care hospitals were examined using the LN strip test and the results were compared with those obtained with a conventional quantitative culture technique. When the results of the leukocyte esterase and nitrite tests were combined, the sensitivity and specificity of the LN strip test were 88.8% and 71.3%, respectively, based on culture results of greater than or equal to 10(5) CFU/ml. Test sensitivity decreased at greater than or equal to 10(4) CFU/ml, whereas test specificity increased.

Leukocyte esterase-nitrite and bioluminescence assays as urine screens

The 1-min leukocyte esterase (LE)-nitrite test (Chemstrip 9; Biodynamics, Division of Boehringer Mannheim Biochemicals, Indianapolis, Ind.) and a bioluminescence assay (Monolight centrifugation method; Analytical Luminescence Laboratory, Inc., San Diego, Calif.) were tested for their efficacy as urine screens among 453 patients at a tertiary-care teaching hospital. Both methods had the capacity to exclude significant bacteriuria (greater than or equal to 10(5) CFU/ml) when compared with the results of conventional culture methods, with predictive values of 99 and 93%, respectively, for a negative test. Bioluminescence was the more accurate nonculture method used. Sensitivity and specificity values were 97 and 71%, respectively, for bioluminescence, 82 and 60%, respectively, for LE with nitrite, and 72 and 64%, respectively, for LE without nitrite. At reduced levels of bacteriuria less than 10(5) CFU/ml), the sensitivities of LE-nitrite and bioluminescence were decreased but comparable. The addition of protein and blood test results in the Chemstrip 9, along with LE-nitrite as bacteriuria indicators, were unsatisfactory because of the large numbers of false-positive results attributed to protein and blood determinations. LE activity as detected by the LE test was a poor predictor of significant bacteriuria in both male and female patients. The sensitivity (71%) and specificity (57%) of the LE test in male patients were significantly lower than those previously reported and varied with the patient population studied.

The clinical microbiology laboratory. Utilization and cost-effectiveness

Utilization of the microbiology laboratory is subject to limitations posed by the diversity of microbial agents causing infection, multiple and often poorly accessible sites of infection, contamination of specimens with indigenous flora, and failure of communication between clinician and microbiologist. Cost constraints increasingly limit the extent of microbiologic services available on-site and lead to decentralization of laboratory services and possible loss of quality control. Increased attention is being paid to process control of cultures, rapid screening and diagnostic tests as culture substitutes, and limitations on antibiotic susceptibility testing.